Angela Onwuachi-Willig, a renowned legal scholar and expert in racial and gender inequality as well as civil rights law, has been named dean of the BU School of Law. A prolific writer and authority on employment discrimination and law as it relates to social injustice, she comes to BU from the University of California, Berkeley, School of Law, where she is the Chancellor's Professor of Law.
Morrison says Onwuachi-Willig, who has published extensively in leading law journals, including the Yale Law Journal, California Law Review, and the Georgetown Law Journal, is a high-impact academic. Prior to her post at Berkeley, she was the Charles and Marion J. Kierscht Professor of Law at the University of Iowa College of Law, as well as a finalist for the Iowa Supreme Court.
Onwuachi-Willig says she made the decision to leave top-ranked UC, Berkeley, School of Law to take the LAW deanship because of the University's commitment to the causes and ideals that she cares deeply about.
"I was initially drawn to BU Law because of its outstanding academic reputation and its amazing community of students, staff, and faculty. The faculty at the law school are stellar. They are highly productive. They write first-rate legal scholarship, and they are as committed to being excellent teachers and mentors for their students as they are to being great legal scholars. The students are also very impressive. They are smart and ambitious. They care not only about being excellent lawyers but also about being excellent citizens in their communities.
Onwuachi-Willig's long list of awards and distinctions includes her 2017–2018 appointment as the William H. Neukom Fellows Research Chair in Diversity and the Law at the American Bar Foundation, and her selection by the National Law Journal as one of the "Minority 40 under 40" lawyers to watch.
In 2013, Yale University Press published her book According to Our Hearts: Rhinelander v. Rhinelander and the Law of the Multiracial Family. The work examines a story that came to her attention because of her own marriage to a white man, that of the interracial marriage between Leo and Alice Rhinelander in 1920s New York. Interracial marriage was legal in the state at that time, but the couple's marriage license identified both parties as white, and when a newspaper reported that Alice Rhinelander was "colored," the events that unfolded altered their lives forever.
Texas native Onwuachi-Willig earned an undergraduate degree from Grinnell College and a law degree from the University of Michigan, where she was a Clarence Darrow Scholar, a Michigan Law Review note editor, and an associate editor for the founding issue of the Michigan Journal of Race and Law. She also holds an MA, an MPhil., and a PhD in sociology and African American studies from Yale University.
Onwuachi-Willig says she is currently delving into historical and social legal work, in particular, the case of Emmet Till, a 14-year-old African American who was lynched in Mississippi in 1955, and Trayvon Martin, a black teenager shot and killed in Florida by a white man in 2012.
As dean, she says, she will be a passionate advocate of keeping the law school financially accessible. She credits Maureen O'Rourke, current LAW dean, who is stepping down to return to her teaching post, with putting the school on an excellent path forward, noting the value the school has placed on diversity.
Members of the eight-person selection committee that recruited Onwuachi-Willig say that her commitment to legal education, extensive mentorship to other academics seeking tenure, and vision for the future of the law school made her a natural choice.
"She has it all," says search committee member Katharine Silbaugh, a LAW professor. "She is an exceptional scholar, recognized as a giant among legal academics, and one of the top writers in race and law today." She also notes Onwuachi-Willig's reputation as a generous mentor to young scholars both inside and beyond where she works. She says references noted her integrity, quiet confidence, drive, and tireless work ethic.
Committee member James E. Fleming, the Honorable Paul J. Liacos Professor of Law and LAW associate dean for intellectual life, says the school's focus on interdisciplinary scholarship, social justice, and public service will likely increase as part of the new dean's vision for LAW. Fleming says Onwuachi-Willig is one of the most important scholars writing about race and the law.
Another committee member, Adil Najam, dean of the Frederick S. Pardee School of Global Studies, says the incoming dean's interdisciplinary scholarship is a boon to BU.
Welcome, Dean Onwuachi-Willig. As another Houstonian now at BU, I understand the Barbara Jordan "draw!" I am excited to learn of you accepting this post, and what an invigorating coup for the University!
Welcome! Blessed to have joined the BU Law student community to benefit from the works and efforts of our phenomenal Dean O'Rourke. I am excited to a part of this new journey with Dean Onwuachi-Willig and hope for continued greatness.
Her education and legal background will be good fit for the rest of the university. Her job will also involve fund raising for Law ,most likely the least favorite but important.
Welcome from a Cal alumni!
Continues to 'recruit ' the best and the brightest since Dr. Brown's tenure; exciting times..
I think it's worth noting that the praises given to Dr. Onwuachi-Willig focus exclusively on things suggesting she is part of the "progressive" tribe: "racial and gender inequality," "social justice," "diversity and inclusion" and, of course, the mess around the death of Trayvon Martin. This story makes the University look like everything middle America finds grating about academia today: pretentious virtue signaling with lots of intellectually patronizing attitudes associating traditionalist white (and black!) Americans with racism and regressiveness. Dr. Onwuachi-Willig may be a fine scholar with balanced views on race, property rights, and individual responsibility in contrast to social justice, but this article frames her in an extremely one-sided fashion.
I think the University and Dr. Onwuachi-Willig would alike be better served by an treatment of this appointment that doesn't reduce and subjugate the scholarship of the incoming LAW Dean and of the Law school to progressive advocacy.
Reduce and subjugate her scholarship? I read this very differently. In fact, the headline expressly states it differently. Dean Onwuachi-Willig is a renowned scholar of racial injustice and inequality and the university is proud of that scholarship. This isn't about appeasing moderates in middle America its about her record of tackling these tough issues in academia throughout her career and how that record will be an asset to BU Law.
I think the University and the Dean (she's not a PhD) are served just fine by this article illuminating her remarkable career and what she will bring to the law school. Judging from the balance of comments here, I think many of the people reading would agree with me. The only person to use the label "progressive" here is you – maybe you should spend some time thinking about that.
I understand some of your concerns. It is does seem strange to study "inequality" as an separate academic subject when the fundamental substrate of the law is its equal application across society. However, I hope that the new Dean's intellectual power, scholarship and leadership will serve the BU community well and wish her the best in her new position.
Your talent and research will be great resource to Boston University School of Law. This great university will be even stronger with your participation and academic scholarship.
Welcome Dean Onwuachi-Willig!!! I am very excited by your credentials and the fact that you will honor The Law School with your services. I hope to have the opportunity to meet you as soon as you settle in at the School. I am at your service!


I've been somewhat of a procrastinator all my life albeit I'm getting much better with age. I used to wait until the last minute to study for a test or to get a paper in on time but somehow I was able to complete and excel at whatever the task was even with my procrastination. This success with procrastination confused me based on all the crap I used to get from my parents and teachers about waiting to the last minute to do things and how bad they felt it was. I didn't put much thought into it until I started reading and learning about time management.
This is why procrastination is so effective for some of us. Think about it, when you waited until the last minute to study for a test what happened when you finally sat down to study? Did you have a bunch of stuff on your desk with music playing and the door of your dorm open for anyone to come in? Or, did you find the deepest, quietest, most secluded place in the library with nothing other than your test book and focused 100% of your attention on learning the material? If you did the latter then your brain was able to focus and absorb the information much more efficiently which is what allowed you to apply the knowledge and pass the test.
The point I'm trying to get across is not to procrastinate, it's to focus. We get pulled in a million different directions in sales and there is always something to do. If we try to do it all at the same time nothing ever seems to get done, or at least it never seems to get done well. If we segment out what we're working on and focus on one thing for a period of time we can get way more done. For example, making 50 dials a day a day is hard when you're writing e-mails, taking breaks, and doing research all at the same time or in between calls. However, if you segment 30 minutes to prep your lists and do research and then segment out an hour on your calendar to do nothing but make the calls, you can make 20-25 quality dials easily in that hour. If you do that twice (once in the morning and once in the afternoon) you've hit your 50 dials in 3 hours total and how you have 5+ more hours to do what you want.
My recommendation is to do everything in one-hour blocks and schedule the time on your calendar for each separate task (research, calls, e-mails, proposals, etc). I treat an hour of cold calling the same way I treat an hour meeting with a client on my calendar in that I don't reschedule it and I don't let people interrupt me.
Block your time, stay focused and Make it Happen!


Methods and systems for calculating tissue oxygenation, e.g., oxygen saturation, in a target tissue are disclosed. In some embodiments, the methods include: (a) directing incident radiation to a target tissue and determining reflectance spectra of the target tissue by measuring intensities of reflected radiation from the target tissue at a plurality of radiation wavelengths; (b) correcting the measured intensities of the reflectance spectra to reduce contributions thereto from skin and fat layers through which the incident radiation propagates; (c) determining oxygen saturation in the target tissue based on the corrected reflectance spectra; and (d) outputting the determined value of oxygen saturation.
This application claims priority to U.S. Provisional Application Ser. No. 60/809,238 entitled "Measuring Tissue Oxygen Saturation," filed on May 30, 2006, the entire contents of which are incorporated herein by reference.
This invention was made with Government support under U.S. Army Medical Research Command Grant Number W81XWH-06-1-0545, and National Space Biomedical Research Institute Grant Number SMS00205, which is funded under NASA Cooperative Agreement Number NCC 9-58. The Government has certain rights in this invention.
This invention relates to measuring properties such as oxygen saturation in tissues.
Tissue oxygen saturation (SO2) provides a measure of oxygen content in red blood cells. Measurement of SO2 in tissue can be used to assess micro-vascular circulation and oxygen supply to tissue cells arising from certain pathologic conditions such as sepsis and diabetes, for example, which result in impaired vascular blood flow. Tissue SO2 measurements can also be used in exercise physiology, where a mismatch between oxygen demand and supply during periods of exercise can be used to determine an extent of physical conditioning of a subject.
Infrared reflectance measurements can be used for non-invasive, quantitative detection of various chemical species in tissue. For example, interrogation of oxygenated and non-oxygenated hemoglobin in tissue can be made via reflectance measurements of the tissue at wavelengths that fall within a range of about 700-1000 nm. In this wavelength range, many chemical species that may be present in the tissue and which are not of interest interact only weakly with incident radiation, and signals arising from hemoglobin can be isolated from signals that arise from other chemical components. Infrared radiation typically penetrates relatively deeply into tissues, and can be used to probe underneath surface tissues such as skin and fat to measure analytes of interest in deeper muscle and other internal tissues. Suitable systems for performing infrared reflectance measurements in tissue are described, for example, in U.S. Publication Number US 2007/0038041 entitled "SYSTEMS AND METHODS FOR CORRECTING OPTICAL REFLECTANCE MEASUREMENTS," filed on Apr. 25, 2006, the entire contents of which are incorporated herein by reference.
Disclosed herein are systems and methods for determining tissue oxygen saturation (SO2) and other quantities such as oxygen tension from infrared spectroscopic measurements. The systems and methods are based, at least in part, on an approach to calculating oxygen saturation in tissue based on an equation for light attenuation by the tissue, where the equation includes terms that correspond to light absorption and scattering by components of the tissue. One form of a light attenuation equation is based on a series expansion (e.g., a Taylor series expansion) of a measured light attenuation spectrum and Beer's law, and includes light attenuation terms that correspond to: absorption by oxygenated heme (hemoglobin and myoglobin), non-oxygenated heme, water, and other chromophores present in the tissue; scattering in the tissue; and a constant factor that arises from experimental conditions. These contributions can be quantitatively determined by a two-stage numerical fitting procedure, which yields concentrations of oxygenated and non-oxygenated heme in the tissue. Tissue oxygen saturation can then be determined from the concentrations of oxygenated and non-oxygenated heme. Other quantities can also be determined from measurements of SO2. For example, oxygen tension (PO2) can be determined from a mathematical equation that relates PO2 to SO2.
Tissue oxygen saturation and/or oxygen tension can function as important physiological diagnostic and/or predictive indicators. In particular, SO2 is a sensitive probe of capillary vasoconstriction, and can be used to track progression and/or treatment of conditions that result in a variation in blood volume in the tissue, or vasoconstriction/vasodilation in response to an insult. Examples of such conditions are hemorrhage, sepsis, heart disease, and diabetes.
In general, in one aspect, the invention features a method for calculating oxygen saturation in a target tissue, where the method includes: (a) directing incident radiation to a target tissue and determining reflectance spectra of the target tissue by measuring intensities of reflected radiation from the target tissue at a plurality of radiation wavelengths; (b) correcting the measured intensities of the reflectance spectra to reduce contributions thereto from skin and fat layers through which the incident radiation propagates; (c) determining oxygen saturation in the target tissue based on the corrected reflectance spectra; and (d) outputting the determined value of oxygen saturation.
Embodiments of the method can include one or more of the following features. Determining oxygen saturation can include determining light attenuation spectra from the corrected reflectance spectra, and calculating oxygen saturation based on concentrations of oxygenated and deoxygenated heme in the target tissue that are derived from the light attenuation spectra, where heme includes hemoglobin and myoglobin in the target tissue. The concentrations of oxygenated and deoxygenated heme can be derived from the light attenuation spectra by fitting the light attenuation spectra to a model light attenuation equation. The light attenuation equation can include a Beer's Law equation that includes terms that correspond to incident light absorption by oxygenated heme, deoxygenated heme, and water in the target tissue. For example, the light attenuation equation can include a series expansion (e.g., a Taylor series expansion) of light attenuation in a plurality of terms that correspond to Beer's Law absorption terms. The fitting can be performed automatically by a processor.
The light attenuation equation can include a term that varies linearly with a wavelength of the incident light, the term having a functional form aλ where a is a constant and λ is the wavelength of the incident light. The value of a can be constrained during fitting so that a assumes only values that are less than or equal to zero. The light attenuation equation can include a constant term independent of the wavelength of the incident light.
Fitting the light attenuation spectra to a model can include performing a two-stage fitting procedure where, in a first stage, initial values of one or more model parameters are determined, and in a second stage, the light attenuation spectra are fitted to the model, where the model includes the initial parameter values determined in the first stage. The light attenuation spectra can be fitted to the model by minimizing a sum of squared differences between the light attenuation spectra and light attenuation values determined from the model.
The light attenuation equation can include a baseline function derived from a difference between light attenuation values determined from the light attenuation equation and the light attenuation spectra. The light attenuation equation can include a differential path length factor that varies directly with a scattering coefficient of the target tissue and inversely with an absorption coefficient of the target tissue. The light attenuation equation can include a diffuse reflectance equation derived from a radiation diffusion model of incident light in the target tissue.
Measuring intensities of reflected radiation can include: (a) measuring, along a first optical path from a light source to a detector, reflected radiation from the target tissue that corresponds to a first source-detector spacing; and (b) measuring, along a second optical path from the light source to the detector, reflected radiation from the target tissue that corresponds to a second source-detector spacing different from the first source-detector spacing. The reflected radiation measured at the first source-detector spacing can include a first weighting of contributions from the target tissue and from tissue layers disposed between the light source and the target tissue, and the reflected radiation measured at the second source-detector spacing can include a second weighting of contributions from the target tissue and from the tissue layers disposed between the light source and the target tissue different from the first weighting. The tissue layers disposed between the light source and the target tissue can be skin and fat layers. Correcting the measured intensities of the reflectance spectra can include reducing contributions from the skin and fat layers to the reflected radiation measured at the second source-detector spacing based on the reflected radiation measured at the first source-detector spacing.
The method can include determining oxygen tension in the target tissue based on oxygen saturation in the target tissue. The method can include assessing a level of vasoconstriction in a patient based on a measurement of total hemoglobin in a target tissue of the patient, where total hemoglobin is determined based on the concentrations of oxygenated and deoxygenated heme in the target tissue.
The target tissue can be within a human. The target tissue can be within an animal. The target tissue can be a muscle tissue.
The plurality of wavelengths can include at least 100 wavelengths or more. The plurality of wavelengths can include wavelengths from 700 nm to 1000 nm (e.g., wavelengths from 725 nm to 880 nm).
Embodiments of the method can also include any of the other method steps disclosed herein, as appropriate.
In another aspect, the invention features a method of monitoring blood volume in a patient, where the method includes: (a) directing incident radiation to a target tissue of the patient and determining reflectance spectra of the target tissue by measuring intensities of reflected radiation from the target tissue at a plurality of wavelengths; (b) correcting the measured intensities of the reflectance spectra to reduce contributions thereto from skin and fat layers through which the incident radiation propagates; (c) determining total heme concentration in the target tissue based on the corrected reflectance spectra; (d) assessing a blood volume in the patient based on the total heme concentration; and (e) outputting the assessed blood volume.
Embodiments of the method can include the following features.
The method can include assessing a stage of progress of at least one of hemorrhage, sepsis, heart disease, and diabetes in the patient based on the assessed blood volume. Embodiments of the method can also include any of the other method steps disclosed herein, as appropriate.
In a further aspect, the invention features a method for calculating oxygen saturation in a target tissue, where the method includes: (a) directing incident radiation to a target tissue and determining reflectance spectra of the target tissue by measuring intensities of reflected radiation from the target tissue at a plurality of radiation wavelengths; (b) determining light attenuation spectra of the target tissue from the reflectance spectra, and fitting the light attenuation spectra to a model light attenuation equation; and (c) determining oxygen saturation in the target tissue based on the fitting of the light attenuation spectra. Fitting the light attenuation spectra to a model can include performing a two-stage fitting procedure where, in a first stage, initial values of one or more model parameters are determined, and in a second stage, the light attenuation spectra are fitted to the model, where the model includes the initial parameter values determined in the first stage.
The model can include a term having a functional form aλ, and where the value of a is constrained during the fitting to be less than or equal to zero. Embodiments of the method can also include any of the other method steps disclosed herein, as appropriate.
In another aspect, the invention features a system that includes a light source configured to direct incident radiation to a target tissue, a detector, and a processor coupled to the detector and configured to: (a) determine reflectance spectra of the target tissue; (b) correct the reflectance spectra to reduce contributions thereto from skin and fat layers through which the incident radiation propagates; and (c) determine oxygen saturation in the target tissue based on the corrected reflectance spectra.
Embodiments of the system can include one or more of the following features.
The processor can be configured to determine reflectance spectra of the target tissue by directing the detector to measure intensities of reflected radiation from the target tissue at a plurality of radiation wavelengths. The processor can be configured to determine oxygen saturation by calculating light attenuation spectra from the corrected reflectance spectra, and calculating oxygen saturation based on concentrations of oxygenated and deoxygenated heme in the target tissue that are derived from the light attenuation spectra, where heme includes hemoglobin and myoglobin in the target tissue.
The system can also include: (a) a first radiation path between the light source and the detector, and corresponding to a first distance between the light source and the detector; and (b) a second radiation path between the light source and the detector, and corresponding to a second distance between the light source and the detector different from the first distance. Incident radiation from the light source can be directed along each of the first and second radiation paths to the target tissue, and reflected radiation from the target tissue can be directed along each of the first and second radiation paths to the detector. The processor can be configured to reduce contributions to the measured reflectance spectra from skin and fat layers by measuring reflectance spectra along each of the first and second light paths, and combining the reflectance spectra to produce corrected reflectance spectra. Each of the first and second radiation paths can include an optical fiber.
The processor can be configured to derive the concentrations of oxygenated and deoxygenated heme in the target tissue by fitting the light attenuation spectra to a model light attenuation equation. The model light attenuation equation can include a Beer's Law equation that includes terms that correspond to absorption of incident radiation by oxygenated heme, deoxygenated heme, and water in the target tissue.
The processor can be configured to determine oxygen tension in the target tissue from oxygen saturation. The processor can be configured to determine total heme concentration in the target tissue from the concentrations of oxygenated and deoxygenated heme in the target tissue. The processor can be configured to assess a blood volume in the target tissue based on the total heme concentration.
The processor can also be configured to perform any of the other method steps disclosed herein, as appropriate.
Oxygen saturation and/or oxygen tension are determined based on light attenuation measurements performed in the infrared region of the electromagnetic spectrum. The effects of absorption and scattering due to analytes other than heme are smaller in this region than in other spectral regions. As a result, heme absorption can be quantitatively isolated from absorption and scattering processes due to other tissue components.
Further, the infrared radiation can penetrate relatively deeply into a patient, interrogating tissue (e.g., muscle tissue) that is located underneath layers of skin and fat. The penetration depth of the infrared radiation permits measurement of oxygen saturation in muscle tissues, for example, which are typically located relatively deeply underneath layers of skin and fat. The infrared spectral data can be corrected for light absorption by skin pigments and light scattering by fat, thereby permitting even more accurate quantitative determination of heme absorption than would otherwise be possible without such corrections. The effects of water absorption in a patient's tissue can also be quantitatively determined and separated from heme absorption.
Measurements are performed across a relatively large number of wavelength channels such as 100 wavelength channels or more (e.g., 150 wavelength channels or more, 200 wavelength channels or more, 400 wavelength channels or more, 600 wavelength channels or more, 1000 wavelength channels or more). The relatively large number of measurements improves the signal-to-noise ratio of the measured data relative to instruments that record data from, for example, between two and six wavelength channels.
The measurements disclosed herein are performed non-invasively using a low cost, portable measurement system. Results can be displayed in real-time or near real-time, which enables continuous monitoring of oxygen saturation and/or oxygen tension. Where these parameters are correlated with a particular medical condition in a patient, the progress of the condition can be evaluated in real-time. The instruments can operate with manual intervention, or in fully automatic mode without operator intervention.
Fitting parameters can be constrained appropriately to enable more accurate quantitative separation of scattering and absorption processes. For example, coefficients of certain wavelength-dependent scattering terms can be constrained to take only non-positive values during fitting of the attenuation equation to measured light attenuation data, to correlate with typical variations in tissue scattering as a function of light wavelength. Appropriate choices of fitting constraints can enable improved quantitative separation of the effects of in vivo tissue scattering and absorption by oxygenated heme.
The light attenuation equation can be fitted to measured data in a two-stage fitting procedure. A first stage of the fitting procedure determines initial values of certain fitting parameters, and a second stage of the fitting procedure determines a lowest-error fit of the measured data to the attenuation equation, starting from the initial values determined in the first stage. The two-stage fitting procedure enables fitting of measured spectral data without intervention by an operator, and reduces the overall time required to perform the fitting procedure. In certain embodiments, the two-stage fitting procedure can also improve the accuracy of the fitting results relative to one-step fitting algorithms.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features and advantages of the invention will be apparent from the description, drawings, and claims.
FIG. 1 is a schematic diagram of one possible embodiment of a spectrometer system for measuring oxygen saturation in a target tissue.
FIG. 2 is a schematic diagram of another embodiment of a spectrometer system for measuring oxygen saturation in a target tissue.
FIG. 3 is a flow chart showing an exemplary series of steps for determining oxygen saturation in a target tissue from light attenuation spectra for the target tissue.
FIG. 4 is a plot showing measured percent change in total hemoglobin as a function of measured percent change in stroke volume for a patient undergoing a lower body negative pressure test protocol.
FIG. 5 is a plot showing measured percent change in total hemoglobin as a function of measured percent change in total peripheral resistance for a patient undergoing a lower body negative pressure test protocol.
FIG. 6 is a plot showing theoretical light attenuation spectra calculated for a non-scattering target tissue at a series of different tissue oxygen saturation values.
FIG. 7 is a plot showing theoretical light attenuation spectra calculated for a scattering target tissue at a series of different tissue oxygen saturation values.
FIG. 8 is a plot comparing actual and estimated values of oxygen saturation in different target tissues.
FIG. 9 is a plot comparing oxygen saturation values measured from withdrawn blood samples and from non-invasive infrared reflectance measurements for patients at various stages of a lower body negative pressure test protocol.
FIG. 10 is a plot comparing oxygen tension values measured from withdrawn blood samples and from non-invasive infrared reflectance measurements for patients at various stages of a lower body negative pressure test protocol.
Disclosed herein are methods and systems for obtaining measurements of tissue oxygen saturation and other physiological quantities such as oxygen tension from infrared reflectance spectra of a target tissue (e.g., a tissue in a human or an animal). Values of these quantities are derived by analyzing a light attenuation model that accounts for tissue absorption and scattering. Reflectance spectra of a target tissue are first measured by a suitably configured spectrometer system, and then the spectra are analyzed, for example, by a processor coupled to the spectrometer system.
A variety of measurement systems can be used to measure attenuation by a target tissue of incident light in the infrared region of the electromagnetic spectrum. FIG. 1 shows a schematic diagram of one embodiment of such a measurement system. Measurement system 10 includes a light source 12, a probe head 14, a detector 16, a processor 18, and a display 19. Light source 12 provides radiation which is coupled into light path 20 and propagates along light path 20 from light source 12 to probe head 14. The radiation emerges from light path 20 and is incident on a surface 32 of a target tissue 30 adjacent to probe head 14. A portion of the incident radiation is reflected by target tissue 30 and enters light path 22. The reflected radiation propagates along light path 22 to detector 16. Detector 16 is configured to measure an intensity of the reflected radiation, as a function of wavelength. Processor 18, e.g., a stand-alone processor or a portion of an external computer system, coupled to detector 16 via communication line 24, provides configuration signals to detector 16. In addition, processor 18 is configured to receive, via communication line 25, the spectral reflectance intensity data recorded by detector 16. Processor 18 can be configured to transform the spectral reflectance data into light attenuation data, for example, that measures wavelength-dependent attenuation of the incident radiation by target tissue 30. As shown in FIG. 1, processor 18 is in electrical communication with display 19. Spectral reflectance data, wavelength-dependent light attenuation data, and/or other data or physiological quantities determined from the measured data, can be output from processor 18 to display 19. Alternatively, or in addition, measured and/or calculated data can be output from processor 18 to another processor (not shown) for further processing, to a storage medium, or to another device (e.g., a computer and/or a wireless communications device).
The ends of light paths 20 and 22 are separated by a distance d in probe head 14. In some embodiments, the distance d can be relatively short, such as about 5 mm or less (e.g., about 4 mm or less, about 3 mm or less, about 2 mm or less, or about 1 mm or less). In other embodiments, the distance d can be relatively long, such as about 20 mm or more (e.g., about 25 mm or more, about 30 mm or more, about 35 mm or more). In certain embodiments, probe head 14 is configured to permit adjustment of the distance d by a system operator. For example, the distance d can be adjusted to acquire spectral data that includes contributions from tissues within a certain depth t of surface 32 of target tissue 30 adjacent to probe head 14. In general, the larger the distance d, the greater the depth of tissue t contributing to the measured light attenuation data.
Light source 12 can, in general, include a wide variety of sources. For example, light source 12 can include an incandescent source, one or more light-emitting diodes, a laser-based source, or other types of sources. Light source 12 can provide radiation in one or more selected regions of the electromagnetic spectrum, such as the ultraviolet region, the visible region, the infrared region, or other regions. In some embodiments, for example, light source 12 is configured to provide radiation in the infrared region of the electromagnetic spectrum. The radiation can include wavelengths from about 700 nm to about 1000 nm, for example.
In certain embodiments, the radiation provided by light source 12 can include multiple wavelengths. For example, a full-width at half maximum of the distribution of wavelengths of the radiation can be about 10 nm or more (e.g., about 20 nm or more, about 50 nm or more, about 100 nm or more, about 150 nm or more, about 200 nm or more, about 250 nm or more). The distribution of wavelengths of the radiation can be produced from a single source element such as an incandescent element or a broadband light emitting diode, for example, or from multiple source elements (e.g., multiple light emitting diodes) operating simultaneously or sequentially.
Light paths 20 and 22 can be formed from materials suitable for directing the radiation provided by light source 12. In certain embodiments, for example, one or both of light paths 20 and 22 can be waveguides formed by one or more optical fibers. In some embodiments, one or both of light paths 20 and 22 can be open passageways formed in probe head 14 and sized to permit the radiation to pass through. In certain embodiments, for example, either or both of light source 12 and detector 16 can be placed in direct contact with the skin of patient, or in direct contact with a target tissue (e.g., without overlying skin and/or fat layers), so that light paths 20 and/or 22 do not include open passageways, but instead include the optical trajectories along which incident and reflected radiation propagate in the target tissue. In some embodiments, one or both of light paths 20 and 22 can include other types of waveguides such as photonic crystal fibers and/or light transmitting polymer materials.
Detector 16 is configured to measure a wavelength-dependent intensity of reflected radiation from target tissue 30. Typically, detector 16 is a spectral detector such as a spectrometer, with a wavelength-dispersing element such as a diffraction grating that is configured for use in a wavelength region that includes the wavelengths in the radiation provided by light source 12. Suitable spectrometers are available, for example, from Ocean Optics Inc. (Dunedin, Fla.). Detector 16 can measure intensities of radiation at multiple wavelengths. For example, in some embodiments, detector 16 is configured to measure the intensity of optical radiation at about 50 or more distinct wavelengths (e.g., about 100 or more distinct wavelengths, about 150 or more distinct wavelengths, about 200 or more distinct wavelengths, about 400 or more distinct wavelengths, about 600 or more distinct wavelengths, about 1000 or more distinct wavelengths).
The spectral intensity data measured by detector 16, which is typically wavelength-dependent reflectance data from target tissue 30, can be converted to wavelength-dependent light attenuation data (e.g., a light attenuation spectrum of target tissue 30) by processor 18 using well known methods. In the subsequent discussion, reference is made to light attenuation spectra of target tissue 30, but the methods and systems disclosed herein can also be used to process spectral reflectance data directly, since the light attenuation and spectral reflectance data are related by a simple mathematical transformation (see, e.g., Equation (2) discussed in the next section).
In addition to converting spectral reflectance data to light attenuation data, processor 18 can be configured to analyze the light attenuation data to obtain measurements of physiologically important quantities such as oxygen saturation and oxygen tension, as will be discussed in further detail below. In general, processor 18 can be configured to perform any of the analysis steps that are discussed herein.
In some embodiments, optical reflectance spectra can be measured at more than one source-detector spacing d. For example, FIG. 2 is a schematic diagram of an embodiment of a measurement system 50 that includes two different source-detector spacings, each of which can be fixed, or adjusted by an operator. Many of the components of measurement system 50 are similar to the components of measurement system 10 and will not be discussed further. Measurement system 50 includes a first detection light path 22 a spaced from light path 20 in probe head 14 by a distance da, and a second detection light path 22 b spaced from light path 20 in probe head 14 by a distance db greater than da.
Spectral reflectance measurements can be recorded by detector 16 at multiple source-detector distances to reduce and/or remove the spectral absorption and/or scattering effects of overlying tissue layers from the spectra of underlying tissues of interest. For example, reflectance spectra recorded at the short source-detector distance da typically include a first weighting of contributions from tissues near surface 32 and from the deeper interior of target tissue 30 (e.g., primarily from tissues near surface 32 of target tissue 30). Reflectance spectra recorded at the longer source-detector distance db typically include a second weighting, different from the first weighting, of contributions from tissues near surface 32 and from the deeper interior of target tissue 30 (e.g., spectra at the longer source-detector distance typically include significant contributions from both tissues near surface 32, and from tissues underlying surface 32). Reflectance data recorded at two different source-detector distances can be processed using suitable algorithms to remove spectral contributions due to overlying tissue layers adjacent to surface 32, retaining primarily spectral contributions due only to the underlying (e.g., deeper) tissue layers. In addition, in some embodiments, the source-detector distances can be adjusted by an operator to improve the selectivity of the spectral reflectance measurements (e.g., to selectively interrogate tissues at particular depths below the surface of a patient's skin).
In some embodiments, spectral reflectance data at multiple source-detector distances can be measured by systems having a single detection light path and multiple source light paths (e.g., multiple paths for coupling light from one or more radiation sources to probe head 14). In general, the particular configuration of the measurement system does not substantially change the processing algorithms used to remove the spectral effects of overlying tissue layers, nor does it change the analysis algorithms that are used to determine quantities such as oxygen saturation and oxygen tension from the light attenuation spectra.
Having measured spectral reflectance data from target tissue 30 and transformed the data into wavelength-dependent light attenuation data corresponding to the target tissue, processor 18 is configured to analyze the light attenuation data to obtain values of quantities of interest for the target tissue. Various analysis algorithms implemented in processor 18 for obtaining these quantities are disclosed below.
where c(HbO2+MbO2) is the total concentration of oxygenated heme in the tissue (Hb=hemoglobin, Mb=myoglobin) and c(Hb+Mb) is the total concentration of deoxygenated heme in the tissue. The sum cHb+Mb+cHbO2+MbO2 is the total concentration of heme in the tissue. Hemoglobin and myoglobin have similar absorption profiles through much of the infrared region of the spectrum, and the infrared reflectance measurement techniques disclosed herein are sensitive to both hemoglobin and myoglobin.
where I0(λ) is an incident light intensity (e.g., the light source intensity), I(λ) is a reflected light intensity from the tissue, λ is a light wavelength, c0 and c1 are constants, <L> is a mean path length of the reflected light through the tissue, εHb(λ) is a wavelength-dependent extinction coefficient for deoxygenated hemoglobin, εHbO2(λ) is a wavelength-dependent extinction coefficient for oxygenated hemoglobin, cwat is a concentration of water in the tissue, and εwat(λ) is a wavelength-dependent extinction coefficient for water. Hemoglobin and myoglobin have similar extinction coefficients in the infrared region of the spectrum, and so the extinction coefficients of oxygenated and deoxygenated hemoglobin are also used to model myoglobin absorption in Equation (2). The determination of values for the various parameters in Equation (2) is discussed in further detail below.
The reference light intensity Iref(λ) typically differs from I0(λ) by a wavelength-independent constant factor, which appears as a constant additive contribution to the experimentally-measured light attenuation spectrum of a target tissue. The constant c0 in Equation (2) accounts for this additive contribution to the light attenuation spectrum. In addition, c0 also accounts for wavelength-independent absorption and/or scattering by chromophores and other species in the target tissue other than hemoglobin, myoglobin, and water. Similarly, the constant c1 accounts for wavelength-dependent light absorption and/or scattering from chromophores and other species in the target tissue other than hemoglobin, myoglobin, and water. Terms on the right-hand side of Equation (2) which are multiplied by <L> account for attenuation of incident light by hemoglobin, myoglobin, and water in the target tissue.
Typically, light attenuation in the target tissue can arise from both light absorption and light scattering processes. For example, light is absorbed by hemoglobin in small blood vessels and myoglobin in cells, by both intravascular and extravascular water, and by melanin pigments in skin. Light can be scattered by physical structures such as blood vessels and muscle fibers, and also by fat which overlies muscle tissue of interest (e.g., fat that is disposed between a probe head of a measurement system and the muscle tissue).
The systems and methods disclosed herein can generally be applied to the calculation of oxygen saturation and other physiological quantities in many different types of tissue, including muscle tissue and non-muscle tissue, and any of the steps discussed in connection with the determination of SO2 can also be performed to calculate SO2 in both muscle tissue and non-muscle tissue. Measuring oxygen saturation in muscle tissue provides a particularly sensitive diagnostic indicator of vasoconstriction/vasodilation, for example.
FIG. 3 is a flow chart 100 that shows a series of steps for calculating oxygen saturation in a target tissue from light attenuation spectra, Aexp(λ), for the target tissue. In a first step 102, one or more light reflectance spectra are collected from a target tissue, and light attenuation spectra are calculated via Equation (3).
In optional step 104, a model Amodel(λ) can be selected to describe light attenuation in the target tissue. In some embodiments, for example, the model selected accounts for both light absorption and light scattering in the target tissue. In certain embodiments, the model includes terms that correspond to one or more of oxygenated hemoglobin and myoglobin, deoxygenated hemoglobin and myoglobin, water, and other species present in the target tissue. A suitable model that can be selected is given by Equation (2), for example. In general, the systems disclosed herein can include one or more models for describing light attenuation in the target tissue. In some embodiments, the systems include only a single model. In certain embodiments, the systems include multiple models, and selection of a model Amodel(λ) can be based on input from a human operator, for example.
where the light attenuation spectra are measured (and theoretical light attenuation values calculated) at a series of wavelengths λi between λmin and λmax. The value of χ2 is minimized to yield values of certain adjustable parameters in Amodel(λ). For example, if the model given by Equation (2) is selected, the function χ2 is minimized to yield values of parameters c0, c1, cHb+Mb, cHbO2+MbO2, cwat, and <L>.
where a and b are constants, with b≦0. Typically, the portions of the measured light attenuation spectra that are due to oxygenated hemoglobin have a positive slope in the infrared region of the spectrum. Thus, when the model given by Equation (2) is selected, parameter c1 can be constrained during fitting so that c1≦0. This constraint enables improved parameter value determination by eliminating cross-talk between contributions to the light attenuation spectra from oxygenated heme, scattering, and a relatively smooth background.
For certain tissues, it may be possible to make good initial estimates for the values of parameters cHb+Mb, cHbO2+MbO2, and cwat (e.g., in healthy human patients). For other tissues, it may be more difficult to arrive at good initial estimates for these parameters. Making initial estimates of parameter values typically involves operator intervention, however, and is subject to variability that arises due to differences in skill levels of human operators. Typically, for example, in healthy human patients, the value of cHb+Mb can be about 40 μmol/L, the value of cHbO2+MbO2 can be about 60 μmol/L, and the value of cwat can be about 60%. These values can be used as initial estimates for the parameters cHb+Mb, cHbO2+MbO2, and cwat.
As an alternative to relying on input from a human operator, the systems and methods disclosed herein can also determine both initial values and final values of model parameters in automated fashion (e.g., without operator input) using a two-stage fitting procedure. The two-stage fitting procedure can, in general, be applied to any of the models disclosed herein to automatically determine good initial values of some or all of the model parameters, and then to determine final parameter values by minimizing the value of χ2 in Equation (4).
As an example, when the model given by Equation (2) is selected in step 104, good initial values of c0, c1, and <L> can be determined using a sweep method by fixing the values of the parameters cHb+Mb, cHbO2+MbO2, and cwat, and using a least-squares minimization procedure to vary the values of parameters c0, c1, and <L>. This technique corresponds to minimizing the value of χ2 in Equation (4) with only c0, c1, and <L> as adjustable parameters. When good initial values of c0, c1, and <L> have been determined via minimization of χ2, these values are fixed and the value of χ2 in Equation (4) is again minimized via the sweep method by allowing parameters cHb+Mb, cHbO2+MbO2, and cwat to vary. The values for these parameters obtained from the minimization procedure correspond to good initial values.
The second stage of the two-stage fitting procedure includes minimizing the value of χ2 in Equation (4) with each of the six parameters c0, c1, <L>, cHb+Mb, cHbO2+MbO2, and cwat allowed to vary (subject to any fitting constraints imposed, as discussed previously), and starting from the good initial values of these six parameters determined in the first stage of the procedure. The values of these parameters obtained after the second stage of the procedure are the final values of the parameters. In general, any fitting algorithm that is capable of minimizing the value of χ2 in Equation (4) subject to any applied constraints can be used in the systems and methods disclosed herein. One example of a fitting algorithm that can be used to minimize value of χ2 in Equation (4) is the Levenberg-Marquardt algorithm.
The two-stage fitting procedure discussed above can provide a number of advantages. In particular, by initiating the second stage of the fitting procedure with good initial values of the parameters, the second stage proceeds more rapidly to convergence than it would otherwise. Also, fitting results are typically more accurate, because the nonlinear least-squares fitting algorithm is less likely to get stuck in a local (but not necessarily global) minimum.
One algorithm that can be used to fit light attenuation spectra to a selected light attenuation model in the disclosed systems and methods is a type of genetic algorithm called the Differential Evolution (DE) method, which is described in Price, K. V., "Differential Evolution: A practical approach to global optimization," (Germany: Springer-Verlag, 2005). The DE algorithm is a global optimization algorithm that converges to an extreme value of a function irrespective of its initial population. The DE algorithm typically converges faster and uses fewer control variables than other global optimization algorithms. Because the DE algorithm converges to a global minimum, the DE algorithm can be used, in some embodiments, without performing the first stage of the fitting procedure discussed above. That is, a one-stage fitting procedure in which the DE algorithm is used to fit light attenuation spectra to a light attenuation model without first fitting the spectra via the sweep method to determine initial estimates of model parameters can be used.
When final values of the model parameters have been determined, oxygen saturation in the target tissue is calculated in step 108. Oxygen saturation is calculated according to Equation (1); therefore, the model selected in step 104 includes parameters cHb+Mb and cHbO2+MbO2. Values of these parameters are determined in step 106, and then SO2 is calculated from the values of these parameters in step 108.
Equation (6) permits straightforward calculation of oxygen tension from oxygen saturation under standard physiological conditions in step 110 of flow chart 100.
Oxygen saturation and/or oxygen tension, measured via the systems and methods disclosed herein, provide a sensitive diagnostic indicator of capillary vasoconstriction in patients. Early in the process of hemorrhage and internal bleeding, capillaries in muscle tissues vasoconstrict to direct blood to the heart and brain where it is most needed. Vasoconstriction also helps to maintain blood pressure at relatively normal levels; as a result, blood pressure typically provides only a late-stage indicator of hemorrhagic shock.
To evaluate the sensitivity of the systems and methods disclosed herein, a set of ten test subjects underwent a test protocol that included progressively increasing magnitudes of lower body negative pressure (LBNP). The LBNP protocol consisted of a five minute baseline period, followed by five minute intervals of chamber decompression to −15, −30, −45, and −60 mm Hg, followed by additional increments of −10 mm Hg every five minutes until either the onset of cardiovascular collapse, or the completion of five minutes at −100 mm Hg. Infrared reflectance spectra were recorded continuously throughout the protocol using a fiber optic sensor with both short-distance and long-distance source-detector spacings. The sensor was placed on the flexor digitorum profundus muscle of the forearm.
Oxygen saturation and oxygen tension in the muscle tissue were calculated from light attenuation spectra generated from the reflectance spectra using the methods disclosed above. The reflectance spectra were corrected to remove contributions from light absorption and/or scattering by skin pigments and fat prior to generating the light attenuation spectra. A blood sample was withdrawn from each test subject in the last minute of each stage of the LBNP protocol. Oxygen saturation for each subject was measured from the blood sample using a co-oximeter instrument, and oxygen tension was measured using a blood gas analyzer.
where p (in units of ohm-cm) is the blood resistivity (typically about 135 ohm-cm), f (in units of cm) is a mean distance between two inner pick-up electrodes, Z0 (in units of ohms) is a mean baseline thoracic impedance, LVET (in units of seconds) is a left ventricular ejection time, and (dZ/dt)min is a height of a measured thoracic impedance vs. time peak (e.g., a Z-point) from a zero line. Cardiac output (Q) was calculated as the product of heart rate (HR) and SV, and TPR was estimated by dividing a mean value of arterial pressure by Q.
FIG. 4 shows the measured percent change in total hemoglobin as a function of the measured percent change in stroke volume. The relationship between the changes in total hemoglobin and stroke volume is approximately linear, as indicated by the solid line in FIG. 4. Without wishing to be bound by theory, one possible explanation for the relationship shown in FIG. 4 is that stroke volume falls as blood volume decreases. In FIG. 5, the percent change in total hemoglobin is plotted as a function of the percent change in total peripheral resistance. The relationship is again approximately linear as shown by the solid line. However, FIG. 5 shows that changes in total hemoglobin are inversely correlated with changes in total peripheral resistance. Typically, total peripheral resistance increases when vasoconstriction occurs. Thus, measurement of total hemoglobin in muscle tissue (by determining concentrations of oxygenated and deoxygenated hemoglobin, as discussed above) provides an accurate diagnostic for the onset and progression of vasoconstriction in patients.
More generally, vasoconstriction and/or vasodilation produce changes in blood volume in a target tissue, and by monitoring total hemoglobin, blood volume in the tissue (e.g., changes in blood volume over time in a patient) can be assessed. Values of SO2 and PO2 determined via the methods disclosed herein also provide sensitive probes of blood volume in a target tissue, and can be used for monitoring and assessment purposes. In general, measurements of quantities such as HbT, SO2, and PO2 are useful for tracking progression and treatment of any disease or condition that results in variation of blood volume in tissues, and/or vasoconstriction/vasodilation in response to an insult. Examples of conditions for which progression can be tracked include: diagnosis of, and evaluation of treatment for, hemorrhage and sepsis; microvascular abnormalities that accompany heart disease and diabetes; and effects of drugs that raise blood pressure through vasoconstriction and/or vasodilation. In animal patients, regional effects of drugs on specific organs can be tracked.
As an example, when a patient undergoes hemorrhaging, the loss of blood volume in certain patient tissues can be monitored by measuring total hemoglobin. Further, as shown in FIGS. 4 and 5, total hemoglobin scales linearly with blood volume. Therefore, by monitoring HbT over time, a stage of progress of a hemorrhage can be assessed. Changes in HbT can be used to assess whether a hemorrhage has been halted or is under control, for example, or whether the hemorrhaging condition is worsening.
As another example, when a patient suffers from sepsis—a microcirculatory disease—small blood vessels in certain tissues of the patient become clogged, resulting in a smaller blood volume (and oxygen-depleted blood) being present in the patient's tissues. Generally, as sepsis persists, the level of oxygen-depletion in blood tissue increases. If perfusion is restored, the sepsis condition is alleviated, and both blood oxygenation and blood volume increase in the patient's tissues. By monitoring HbT and/or SO2 and/or PO2 in patient tissues, as disclosed herein, the rate of progress of sepsis can be assessed. For example, when a sepsis condition in a target tissue is worsening, the value of HbT in the tissue decreases with decreasing blood volume. As sepsis in the tissue is alleviated, the value of HbT in the tissue increases with increasing blood volume. Similar correlations apply to assessing sepsis based on blood volume determined from measurements of SO2 and PO2 in the target tissue.
As a third example, when a patient suffers from heart disease or diabetes, atherosclerosis which results from these conditions prevents vasoconstriction in response to a challenge. In contrast, in a healthy patient, vasoconstriction in response to a challenge occurs to maintain blood pressure. Thus, progress of a condition such as heart disease or diabetes can be assessed by monitoring HbT and/or SO2 and/or PO2 in the patient. Typically, for example, a patient suffering from one of these conditions is either tilted or subjected to an exercise protocol which represents a challenge, and values of SO2 and/or PO2 and/or and HbT are determined from a selected target tissue of the patient. Due to the inability of the patient's blood vessels to vasoconstrict, measured changes in SO2 and/or PO2 and/or and HbT for the patient will be smaller than the measured changes in these parameters would be for a healthier patient. By measuring the difference in the values of SO2 and/or PO2 and/or and HbT for the afflicted patient's tissue relative to standard values for a healthy patient's tissue (or relative to values of these parameters measured from the same patient at an earlier stage of the disease), the progress of conditions such as heart disease and diabetes can be assessed.
In general, as discussed above, measurements of quantities such as HbT, SO2, and PO2 for assessment and tracking of various conditions are performed during interventions that stimulate vasoconstriction to maintain blood pressure and/or vasodilation to improve blood flow. Examples of such interventions include occluding one or more blood vessels, exercising a subject, and tilting a subject.
The equations and algorithms disclosed herein can be implemented in hardware or in software, or in a combination of both. The method steps and figures disclosed herein can be implemented in computer programs using standard programming techniques. The programs can be designed to execute on programmable processors (such as processor 18) or computers, e.g., microcomputers, each including at least one processor, at least one data storage system (including volatile and non-volatile memory and/or storage elements), at least one input device, such as a keyboard or push button array, and at least one output device, such as a CRT, LCD, or printer. Program code is applied to input data to perform the functions described herein. The output information is applied to one or more output devices such as a printer, or a CRT or other monitor, or a web page on a computer monitor with access to a website, e.g., for remote monitoring.
Each program used in the systems disclosed herein is preferably implemented in a high level procedural or object oriented programming language to communicate with a computer system. However, the programs can be implemented in assembly or machine language, if desired. In any case, the language can be a compiled or interpreted language.
Each such computer program can be stored on a storage medium or device (e.g., ROM or magnetic diskette) readable by a general or special purpose programmable computer, for configuring and operating the computer when the storage medium or device is read by the computer to perform the procedures described herein. The programs can also be considered to be implemented as a computer-readable storage medium, configured with a computer program, where the storage medium so configured causes a processor in the computer to operate in a specific and predefined manner to perform the functions described herein.
Although any communications network can be used to obtain results from remote monitoring, the Internet or wireless systems provide useful choices to transmit data.
The invention is further described in the following examples, which are not intended to limit the scope of the invention described in the claims.
To evaluate the accuracy of the systems and methods disclosed herein, simulated tissue attenuation spectra were calculated for four different light scattering conditions in a target tissue, and the method steps of FIG. 3 were applied to the data from each of the four light scattering conditions to determine values of oxygen saturation. The four light scattering conditions correspond to four different target tissues of interest. For each target tissue, simulated light attenuation spectra were calculated for each of eight different theoretical SO2 values: 0%, 10%, 20%, 40%, 50%, 60%, 80%, and 100%.
where L is a path length of the attenuated light through the target tissue, cHb, cHbO2, and cwat are concentrations of deoxygenated hemoglobin, oxygenated hemoglobin, and water in the target tissue, respectively, and εHb(λ), εHbO2(λ), and cwat(λ) are extinction coefficients of deoxygenated hemoglobin, oxygenated hemoglobin, and water as a function of the wavelength λ. Values of these parameters were selected to generate light attenuation spectra for a non-scattering, absorbing target tissue.
Equations (11)-(13) are described in Matcher, S. J. et al., "In vivo measurements of the wavelength dependence of tissue-scattering coefficients between 760 and 900 nm measured with time-resolved spectroscopy," Applied Optics, 36:386-396 (1997). In Equations (11)-(13), μs′(λ) is in units of cm−1 and λ is in units of nm. Light attenuation spectra for the three different target tissues corresponding to Equations (11)-(13) were calculated at a series of wavelength points between 725 nm and 880 nm.
where N is the number of light attenuation spectra, and ŷi and yi are theoretical and experimentally determined values of SO2, respectively. Relatively large values of R2 (e.g., values approaching unity) and relatively small values of RMSEP indicate that the experimentally determined SO2 values are accurate (e.g., match the theoretical SO2 values closely).
Simulated light attenuation spectra calculated using Equation (8) are shown in FIG. 6 for a series of theoretical values of SO2. The light attenuation spectra in FIG. 6 correspond to a target tissue that does not scatter incident light (e.g., light attenuation occurs by absorption only). Simulated light attenuation spectra calculated for a light scattering target tissue that corresponds to a forearm of a patient are shown in FIG. 7 for a series of theoretical values of SO2. In each of FIGS. 6 and 7, a water concentration cwat of 60% and a source-detector spacing d of 3 cm were used in the calculations.
FIG. 8 is a plot showing actual (theoretical) and estimated (measured) values of SO2, determined by fitting the four sets of light attenuation spectra calculated using Equations (8)-(13) to the model given by Equation (2) according to the procedure shown in FIG. 3. The fitting algorithm used was a Levenberg-Marquardt optimization method with initial parameter values obtained from the sweep technique discussed above. Values of R2 between 0.99 and 1 were obtained for each of the four sets of attenuation spectra (e.g., for each of the four different target tissues), with a maximum RMSEP of less than 5% SO2. The relatively high values of R2 and relatively low RMSEP values indicate that accurate measurements of SO2 in each of the four target tissues were achieved. For comparison, the theoretical light attenuation spectra were also fitted to Equation (2) using a DE algorithm, and the values of the model parameters obtained from the fitting procedure were used to calculate SO2 values. The results are shown in Table 1 below. For three of the four target tissues, the RMSEP for SO2 determined via the DE algorithm was lower than the RMSEP for SO2 determined via the Levenberg-Marquardt algorithm.
To simulate the early stages of hemorrhagic shock in human patients, a test protocol that included progressively increasing magnitudes of lower body negative pressure (LBNP) in five human test subjects was performed. The LBNP protocol consisted of a five minute baseline period, followed by five minute intervals of chamber decompression to −15, −30, −45, and −60 mm Hg, followed by additional increments of −10 mm Hg every five minutes until either the onset of cardiovascular collapse, or the completion of five minutes at −100 mm Hg. Infrared reflectance spectra were recorded continuously throughout the protocol using a fiber optic sensor with both short-distance and long-distance source-detector spacings. The sensor was placed on the flexor digitorum profundus muscle of the forearm.
FIG. 9 shows the correlation between oxygen saturation measured from withdrawn blood samples (O2Hb (%) blood) and oxygen saturation measured via infrared reflectance measurements (NIRS SO2(%)) at various stages of the LNBP protocol for each of the five test subjects. FIG. 10 shows the correlation between oxygen tension measured from withdrawn blood samples (Venous PO2) and oxygen tension measured via infrared reflectance measurements (NIRS PO2) during the LNBP protocol for each of the five subjects. In FIG. 9, the RMSEP in SO2 is about 8%, and in FIG. 10, the RMSEP in PO2 is about 3.3 mm Hg. These relatively low errors of prediction indicate that SO2 and PO2 values determined via infrared reflectance measurements correspond accurately to actual SO2 and PO2 values in target tissues. The accuracy of the SO2 and PO2 values further indicates that the systems and methods disclosed herein provide accurate and sensitive diagnosis of conditions such as hemorrhagic shock in patients.
The systems and methods disclosed herein can make use of other light attenuation models (e.g., models other than Equation (2)) to determine SO2 and other physiological quantities such as PO2 in target tissues. Three different alternative models will be discussed; other models are also possible. The following alternative models have been investigated for accuracy by fitting sets of theoretical light attenuation spectra generated using Equations (8)-(13), and corresponding to four different target tissues (e.g., non-scattering tissue, forearm tissue, calf tissue, and intact head tissue), to each of the models, and calculating coefficients of determination and RMSEP values for values of SO2 determined for each target tissue using each model.
where Âexp(λ) is the light attenuation model function given by Equation (2) with the best-fit parameter values.
In the model given by Equation (16), c2 is a scale factor that is varied along with the other fitting parameters. From refined values of cHb+Mb and cHbO2+MbO2 that are obtained by fitting Equation (16) to the measured light attenuation spectra, values of SO2 and PO2 are calculated.
This multi-step fitting procedure—first, to determine baseline spectrum bspect(λ), and second, to determine SO2 and PO2 from fitted values of the parameters in Equation (16)—provides for more accurate determination of the parameters in Equation (16), and therefore, more accurate SO2 and PO2 values. Table 2 below shows R2 and RMSEP values calculated for each of the four different theoretical target tissues for which light attenuation spectra were simulated using Equations (8)-(13). Values of SO2 determined from fitting the theoretical light attenuation spectra using the multi-step fitting procedure discussed above were compared to the theoretical values of SO2, which yielded an R2 value of 0.99 for each of the tissues, and RMSEP values of less than 6% SO2. The relatively large R2 values and relatively low RMSEP values indicated that Model 2 provided accurate determination of SO2 in target tissues.
where μa(λ) and μs(λ) are wavelength-dependent absorption and scattering coefficients of the target tissue, respectively, c1 is a constant, d is a source-detector distance, and dpf(λ) is a differential path length factor for the tissue. The scattering coefficient μs(λ) is related to the reduced scattering coefficient μs′(λ) according to μs′(λ)=(1−g)μs(λ), where g is an anisotropy factor that corresponds to an average cosine of the scattering angle.
During the fitting procedure, constraints are imposed on c3 so that c3<0.
A nonlinear Levenberg-Marquardt least-squares fitting procedure was used to determine values of the various model parameters by fitting the theoretical (e.g., simulated) light attenuation spectra to the model given by Equations (18)-(21). Values of SO2 were then calculated from the fitted values of the parameters in Equation (19). Table 3 below shows R2 and RMSEP results from a comparison of experimentally determined SO2 values and theoretical SO2 values. As shown in the table, R2 values were 0.97 or larger for all four target tissues, and RMSEP values were less than 10% SO2. These statistical measures indicate that Model 3 provided for accurate determination of SO2 in the target tissues.
Comparing to the results for Model 2, Model 3 appears to provide slightly less accurate results on average for the test data evaluated herein. However, for certain tissues, Model 3 may provide more accurate SO2 determinations (e.g., compare results for intact head target tissue).
A two-stage nonlinear least-squares fitting procedure was used to determine parameters of the model given by Equations (19), (20), and (22)-(24) by fitting the equations to the theoretical data for each of the four different target tissues. In a first stage of the fitting procedure, prior to performing a fit of all of the model parameters to the data, a good initial value of the parameter C was obtained by using the sweep method. Values of the parameters c0, c2, c3, cHb+Mb, cHbO2+MbO2, and cwat, were held constant, and the theoretical light attenuation spectra were fitted to Equation (24), allowing only C to vary among the model parameters. Fitting the data to Equation (24) included minimizing a sum of squared differences, χ2, between the model and the theoretical data, as discussed in connection with Equation (4). The value of C obtained from the sweep method corresponded to a good estimate for parameter C.
In the second stage of the fitting procedure, the value of C determined in the first stage was used as the final value of C in Equation (22) (e.g., fixed as a constant), and the theoretical light attenuation spectra were again fitted to Equation (24), permitting each of the parameters c0, c2, c3, cHb+Mb, cHbO2+MbO2, and cwat to vary during fitting. In this manner, accurate values of the six parameters were obtained, and SO2 in each of the target tissues was calculated based on the values of cHb+Mb and cHbO2+MbO2 from the fitting procedure. Table 4 below shows R2 and RMSEP results from a comparison of experimentally determined SO2 values and theoretical SO2 values. As shown in the table, R2 values were 0.99 for all four target tissues, and RMSEP values were less than 7% SO2. These statistical measures indicate that Model 4 provided for accurate determination of SO2 in the four target tissues. Based on the R2 and RMSEP values, the results for each of Models 2, 3, and 4 achieved comparable accuracy.
correcting the measured intensities of the first reflectance spectrum based on the measured intensities of the second reflectance spectrum.
2. The method of claim 1, wherein determining oxygen saturation comprises determining light attenuation spectra from the corrected reflectance spectra, and calculating oxygen saturation based on concentrations of oxygenated and deoxygenated heme in the target tissue that are derived from the light attenuation spectra, wherein heme comprises hemoglobin and myoglobin in the target tissue.
3. The method of claim 2, wherein the concentrations of oxygenated and deoxygenated heme are derived from the light attenuation spectra by fitting the light attenuation spectra to a model light attenuation equation.
4. The method of claim 3, wherein the light attenuation equation comprises a Beer's Law equation comprising terms that correspond to incident light absorption by oxygenated heme, deoxygenated heme, and water in the target tissue.
5. The method of claim 4, wherein the light attenuation equation comprises a series expansion of light attenuation in a plurality of terms that correspond to Beer's Law absorption terms.
6. The method of claim 5, wherein the series expansion of light attenuation comprises a Taylor series expansion of light attenuation.
7. The method of claim 4, wherein the light attenuation equation further comprises a baseline function derived from a difference between light attenuation values determined from the light attenuation equation and the light attenuation spectra.
8. The method of claim 4, wherein the light attenuation equation further comprises a differential path length factor that varies directly with a scattering coefficient of the target tissue and inversely with an absorption coefficient of the target tissue.
9. The method of claim 3, wherein the light attenuation equation comprises a term that varies linearly with a wavelength of the incident light, the term having a functional form aλ where a is a constant and λ is the wavelength of the incident light.
10. The method of claim 9, wherein the value of a is constrained during fitting so that a assumes only values that are less than or equal to zero.
11. The method of claim 3, wherein the light attenuation equation comprises a constant term independent of a wavelength of the incident light.
12. The method of claim 3, wherein fitting the light attenuation spectra to a model comprises performing a two-stage fitting procedure wherein, in a first stage, initial values of one or more model parameters are determined, and in a second stage, the light attenuation spectra are fitted to the model, wherein the model comprises the initial parameter values determined in the first stage.
13. The method of claim 12, wherein the light attenuation spectra are fitted to the model by minimizing a sum of squared differences between the light attenuation spectra and light attenuation values determined from the model.
14. The method of claim 3, wherein the fitting is performed automatically by a processor.
15. The method of claim 3, wherein the light attenuation equation comprises a diffuse reflectance equation derived from a radiation diffusion model of incident light in the target tissue.
16. The method of claim 2, further comprising assessing a level of vasoconstriction in a patient based on a measurement of total hemoglobin in a target tissue of the patient, wherein total hemoglobin is determined based on the concentrations of oxygenated and deoxygenated heme in the target tissue.
17. The method of claim 1, wherein correcting the measured intensities of the first reflectance spectrum comprises reducing contributions from the skin and fat layers to the first reflectance spectrum based on the measured intensities of the second reflectance spectrum.
18. The method of claim 1, further comprising determining oxygen tension in the target tissue based on oxygen saturation in the target tissue.
19. The method of claim 1, wherein the target tissue is within a human.
20. The method of claim 19, wherein the plurality of wavelengths comprises wavelengths from 725 nm to 880 nm.
21. The method of claim 1, wherein the target tissue is within an animal.
22. The method of claim 1, wherein the plurality of wavelengths comprises at least 100 wavelengths or more.
23. The method of claim 1, wherein the plurality of wavelengths comprises wavelengths from 700 nm to 1000 nm.
24. The method of claim 1, wherein the target tissue is a muscle tissue.
26. The method of claim 25, further comprising assessing a stage of progress of at least one of hemorrhage, sepsis, heart disease, and diabetes in the patient based on the assessed blood volume.
28. The method of claim 27, wherein the model comprises a term having a functional form aλ and wherein the value of a is constrained during the fitting to be less than or equal to zero.
30. The system of claim 29, wherein the processor is configured to determine reflectance spectra of the target tissue by directing the detector to measure intensities of reflected radiation from the target tissue at a plurality of radiation wavelengths.
31. The system of claim 29, wherein the processor is configured to determine oxygen saturation by calculating light attenuation spectra from the corrected reflectance spectra, and calculating oxygen saturation based on concentrations of oxygenated and deoxygenated heme in the target tissue that are derived from the light attenuation spectra, wherein heme comprises hemoglobin and myoglobin in the target tissue.
32. The system of claim 31, wherein the processor is configured to derive the concentrations of oxygenated and deoxygenated heme in the target tissue by fitting the light attenuation spectra to a model light attenuation equation.
33. The system of claim 32, wherein the model light attenuation equation comprises a Beer's Law equation comprising terms that correspond to absorption of incident radiation by oxygenated heme, deoxygenated heme, and water in the target tissue.
34. The system of claim 31, wherein the processor is further configured to determine total heme concentration in the target tissue from the concentrations of oxygenated and deoxygenated heme in the target tissue.
35. The system of claim 34, wherein the processor is further configured to assess a blood volume in the target tissue based on the total heme concentration.
36. The system of claim 29, wherein the first and second source detector distances correspond to first and second radiation paths between the light source and the detector, and each of the first and second radiation paths comprises an optical fiber.
37. The system of claim 29, wherein the processor is further configured to determine oxygen tension in the target tissue from oxygen saturation.


With the month of June already over the halfway point, I thought it'd be a good time to reevaluate some of my personal reading goals for the second half of the year. It's always a good idea to take some time for personal reflection, even if it's just over your reading habits! With that being said, here are some reading goals that I'd like to start/continue with for the rest of 2018.
Read at least one book from a subscription box per month.
Right now, I have an excess of books built up from previous book boxes. I haven't been very good at picking them up in a timely manner and it's really time to start. I'll probably focus on books I've received from Book of the Month Club first, as I feel like those are the ones I've pushed to the side more than ones from other boxes.
2. Finish/catch up on a series before starting a new one.
Let's be real, we all start wayyyyy too many series and have the hardest time finishing them in a timely manner. I really need to try and not do that so much! I've been doing a pretty good job on catching up/finishing series during the first half of the year and so I want to focus on continuing with that. It makes me feel so accomplished when I finish a series, haha!
3. Focus more on reading books that have been on my shelves/TBR for a long time.
I own close to 300 books and half of those are unread which isn't something I'm really proud of. I hope to remedy some of that for the rest of the year, by focusing more on my backlisted titles. I know how much I love all of the shiny new preorders that show up at my house on their release date, but I really need to learn to push them aside for just a little while. Stay strong, Larkin!
4. Read at least one diverse book a month.
I've actually been doing really good about this during the first half of the year, but I really want to continue doing so far the rest of the year. I actually have a Native American own voices novel up next on my TBR which I'm really excited to get to!
5. Be okay with DNFing books that I'm not enjoying.
I really struggle with DNFing books. I always feel like I'm failing if I don't actually try and push myself to finish the book that I'm reading. However, I think it's a good idea to know when something doesn't work for you and to be okay with that. I was recently listening to the audiobook of Call Me By Your Name, and since it's such a beloved book, I was struggling to continue listening to it because I thought maybe I would enjoy it if I just stuck with it. But after a few hours into it, I knew that it wasn't going to work for me based on the writing style. And surprisingly enough, I felt so much better after I DNFed and moved on to a different book that I enjoyed so much more.
What are some of your personal reading goals for the rest of the year? Do you like to reflect on your reading goals throughout the year? Do you have any of the same reading goals as me?
I really need to get better about reading books from my subscription boxes, too! I always put them aside so I can read other books and I feel terrible about it.
Yes, I do the same thing! Unless it's a book that I've been looking forward to, it just gets stuck on my bookshelves and then I'll forget about it. I've got to kick that habit real quick, haha!
I never really feel ok with DNFing Books it's the hardest thing for me.
I was the same way for the longest time. I only just started doing it a couple of times this past year. It's definitely still a work in progress for me.
I also need to get better at both finishing series and DNF ing books I'm not enjoying.
Yeah, I'll probably cancel all of my subscriptions except one since it tends to send out books that I probably wouldn't hear about normally. I think I've reached the point where I just want the books and candles and I can buy those separately for a lot cheaper, haha!
I really need to start reading books from subscription boxes sooner too, I just let them build up and up. I joined a reading challenge this year to read some of my tbr and it's going ok, I really need to stop signing up for arcs then id be home free!!
That's exactly what I do too! Hopefully I can fix some of the buildup and start reading them sooner. I just have so many! Haha!
I might try and read 1 a month…..well that's the idea…..hope it works in practice!!!
Ooh this type of post is such a good idea – I think I may need to do one of my own since this year has been kind of crazy for me and I've gotten off track with my reading and blogging BIG TIME this year.
I definitely need to focus a bit on my own backlist titles as well. I have SO MANY books and I have read embarrassingly few of them. I feel like all of us bookworms struggle with this, haha.
Yeah, I know exactly how you feel!
You are so creativity .


text:
Laurel Blair Salton Clark (Ames, 10 maart 1961 – boven de staat Texas, 1 februari 2003) was een Amerikaans ruimtevaarder. Clarks eerste ruimtevlucht was STS-107 met de spaceshuttle Columbia en vond plaats op 16 januari 2003. De zevenkoppige bemanning overleed op 1 februari 2003 nadat de shuttle tijdens de terugkeer in de dampkring uiteenviel.

Clark was een chirurg bij de Amerikaanse marine, die haar opleiding volgde bij het elitekorps Navy Seals. Ze werd in 1996 astronaut bij NASA.

Planetoïde 51827 Laurelclark werd naar haar vernoemd.

Clark, Laurel

redpajama_set_name: RedPajamaWikipedia


text:
Reported domestic violence in Scotland falls. Is this part of wider change?
January 16, 2018 johnrobertson834
A few years ago, Frankie Boyle suggested that Scotland should become an Islamic Republic but that it would mean we'd have to treat our women better. I know, it was a joke but it played to a negative stereotype of the Scots which is increasingly under attack by facts on the ground.
Stereotypes take a long time to change. Comedians and, sometimes, TV drama writers, continue to characterise Scots as violent, drunken and mean. Similarly, the Welsh, are regularly portrayed in negative ways. In sharp contrast, ethnic and religious minorities are treated with care and, after some time, the Irish are rarely stereotyped in the ways they were in earlier times. Is it because we, the Scots and the Welsh, is not independent?
Reports that domestic abuse in Scotland have dropped from those of 2016 by 6.1% may suggest another example. The figures are still horrible though. Between December 10th 2017 and January 7th 2018, there were 4 799 reported incidents, down from 5 111 over the same period the previous year.
https://www.eveningexpress.co.uk/news/scotland/fall-in-number-of-reports-of-domestic-abuse-over-the-festive-period/
Not only are reports of domestic violence falling in Scotland but they are falling well below those of England. See this diagram from the Joseph Rowntree Foundation in 2017:
From: 'UK Poverty 2017 A comprehensive analysis of poverty trends and figures' Report by the JRF Analysis Unit
Domestic violence is, for all age and deprivation-level groups, lower in Scotland than in England. It would be really interesting to have a precise gender breakdown for the Scottish figures to compare with the shocking level in one of the groups above – 10%!
I've already reported on other changes which challenge the negative Scottish stereotype. See these:
Racial hate crimes increase by 33% in England & Wales while falling by 10% in Scotland: Who says we're not different?
Scotsman headline is untrue: hate offences against Jews in Scotland are extremely rare by contrast with the rest of the UK?
Scotland's homicide rate falls by 47%, is lower than the rate for England and Wales and has fallen faster than many other countries in the ten years of SNP government
Extracting the positives for Scottish Government from the Joseph Rowntree Foundation report on Poverty which you are unlikely to hear of elsewhere: Lower poverty, better qualified workers, lower domestic violence, smaller educational gaps and eating just as much fruit!
Scotland takes nearly 26% of Syrian refugees settled in UK with only 8% of the UK population
UN condemns UK Government's 'human catastrophe' on disability rights but praises Scottish Government's actions
Footnote: I'll do a separate report on how safe Scottish university cities are by contrast with those elsewhere in the UK. It's shocking.
Previous Article Scotsman must stop pandering to Brian Monteith's hypocrisy aboot 'whitabootery'
Next Article Scotland's university cities by far the safest places to send your children
6 thoughts on "Reported domestic violence in Scotland falls. Is this part of wider change?"
Alasdair Macdonald. January 16, 2018 / 4:13 pm
The former Strathclyde Police Violence Reduction Unit did sterling groundbreaking work in this regard, and, despite the problems of Police Scotland and the exaggerations of the unionists (who, with a conditional objection by the LibDems) favoured its creation, the VRU has continued. John Carnochan has now retired, but continues to preach the gospel and the current leader, Karen McCluskey is a formidable, assertive and articulate advocate. Projects like Navigator based at Glasgow and Edinburgh Royal Infirmaries – you know, the hospitals described in a box pop in one of our papers, as having 'scenes worse than Syria and Iraq' – have quietly supported victims of crime and, as important, have persuaded others that there are other ways than violence, by getting them involved in useful activities which develop self respect, fellow feeling, and independence.
During the city riots in England, during Mr Cameron's Premiership, the Unit was invited to Downing St to discuss approaches, because their had been no disorder in Scotland's cities. Mr Cameron had condemned the violence in BRITAIN's cities until Alex Salmond pointed out the absence of rioting in Scotland. Of course this was met by derision by the Tories and their media mob, and some of the Scottish branch tried to show that the kinds of youthful misconduct that occurs in all cities, towns and even villages, was 'riotous behaviour'.
johnrobertson834 January 16, 2018 / 10:12 pm
Yes I remember that well.
Ludo Thierry January 16, 2018 / 6:34 pm
Hi Alasdair – am I correct in remembering that Police Scotland 'lent' several hundred Police Officers to one or more of the English Police Authorities? To 'lend a helping hand' in undertaking routine duties whilst the local Police were rather involved trying to stem the periods of looting (and sadly some elements of fire-raising as I recall) in their own patches? – (By the way – I'm positive baron Mike Watson would have been somewhere else at the time!). In view of the 'helping hand' from Police Scotland the Cameron attempt to paint the episodes of street rioting/looting/fire-raising as UK -wide phenomena was particularly galling.
Alasdair Macdonald January 16, 2018 / 7:16 pm
Lido, I do not recall the 'lending' to which you refer. However, lending officers between different authorities is not unknown. Some time ago, I had to attend an event at the Palace of Holyroodhouse and there were officers from Lancashire and Essex on the entrances.
They also tried to teach New York polis to be less trigger happy.
See: https://thoughtcontrolscotland.com/2017/10/25/first-new-york-police-and-now-canadas-police-come-to-learn-from-scotlands-successes-in-tackling-violence/
and: https://thoughtcontrolscotland.com/2016/02/21/scottish-news-media-conceal-global-status-of-police-scotlands-methods/
Pingback: Of 35 children and teenagers killed with knives in Britain in 2017, not one was in Scotland, yet in 2005, the UN called Scotland the most violent country in the developed world. – Talking-up Scotland

redpajama_set_name: RedPajamaCommonCrawl


Everyone loves spending time outside, but we're all more conscious than ever before that there is such a thing as too much of a good thing. In the case of sunlight and exposure to the sun's UV rays that certainly couldn't be any more true. The Caravan Displayshade Canopy is an outdoor shelter designed around the idea that protection from overexposure to the sun can be just as important as making sure that you stay out of the wind and rain when you're spending time outdoors.
While sun coverage is a critical function of this shelter, there are lots of other important design features to consider. The frame is constructed of lightweight steel, providing added strength, stability, and security to all of your outdoor activities. Similarly, full truss design, ABS foot pads, and pull-pin height adjustment provide for your comfort and safety underneath the tent while they add to your overall relaxation and enjoyment no matter what activity you're engaged in. And, of course, the professional-grade 500 denier polyester top is intended specifically to ensure ultimate protection from potentially harmful UV rays. No matter what color you choose for the top, you can rest assured that you're getting that maximum level of SPF protection you're looking for.
This is obviously the type of shelter lots of people gravitate towards for events that will keep them out in the sun for long periods of time. Afternoon tailgates, days at the beach, outdoor festivals, and craft fairs are all areas where the preventive capabilities the Displayshade brings to the table really come in handy. But, in a more general sense, this shelter is equally well-suited for use where you'd employ a canopy to protect you from potentially adverse weather conditions such as an alfresco dinner, an outdoor party or event, or a family get-together. Sun protection is just one of the draws of this versatile tent, which is probably why it's such a popular item.
In other words, don't let the name or the stated purpose of the Caravan Displayshade Canopy fool you. It's just as at home keeping raindrops off of you, your friends, and your family as it is warding off a sunburn. When you need quick, reliable shelter and you're not interested in paying tons of money, this popular personal tent model is definitely worth a look.


text:
Structure, composition and dynamics of a calcareous grassland metacommunity over a 70-year interval
Newton, Adrian C.; Walls, Robin M.; Golicher, Duncan; Keith, Sally A.; Diaz, Anita; Bullock, James M.. 2012 Structure, composition and dynamics of a calcareous grassland metacommunity over a 70-year interval. Journal of Ecology, 100 (1). 196-209. https://doi.org/10.1111/j.1365-2745.2011.01923.x
Official URL: http://onlinelibrary.wiley.com/doi/10.1111/j.1365-...
1. Calcareous grasslands are communities of high conservation value, often characterized by high plant species richness. These grasslands have experienced a major decline in area throughout Europe, principally resulting from agricultural intensification. Although they have been the focus of extensive previous research, few attempts have been made to examine the long-term dynamics of multiple communities at the landscape scale. 2. To assess long-term change in the structure and composition of a calcareous grassland metacommunity, 88 extant sites first surveyed by R. Good in the 1930s were resurveyed in 2009. Values of α-, β- and γ-diversity were compared between the two surveys, using a one-way analysis of similarity (ANOSIM) and non-metric multidimensional scaling. Elements of metacommunity structure (EMS) analysis was used to identify metacommunity structure, and changes in metacommunity composition were related to plant traits. 3. Analyses indicated that α-diversity increased over time, with mean (±SD) species richness per site increasing from 29.31 ± 7.65 in the 1930s to 40.18 ± 16.41 in 2009. No change in β-diversity was recorded. However, γ-diversity increased, with the total number of species rising from 219 in the 1930s to 280 in 2009. Species composition shifted over time, associated with a decline in 'stress-tolerant' species typical of species-rich calcareous grasslands, and an increase in species typical of mesotrophic grasslands. This was associated with an increase in mean Ellenberg N value, suggesting that eutrophication has been a driver of floristic change. 4. Elements of metacommunity structure analysis indicated that the structure of this grassland plant metacommunity was Clementsian at both survey times, indicating species sorting. Metacommunity structure was stable over time, despite changes in α- and γ-diversity. Analysis of potential structuring mechanisms revealed a significant influence of elevation. 5. Synthesis. This investigation provides a rare example of the long-term dynamics of a plant metacommunity. Results indicate that substantial change has occurred in the composition of calcareous grasslands during this time, both at local and regional scales. The investigation provides evidence of the impact of environmental change on immigration and extinction processes operating in calcareous grasslands at different scales, and highlights challenges for their future conservation.
CEH Topics & Objectives 2009 - 2012 > Biodiversity > BD Topic 1 - Observations, Patterns, and Predictions for Biodiversity
CEH Topics & Objectives 2009 - 2012 > Biodiversity > BD Topic 2 - Ecological Processes in the Environment
biodiversity, conservation, determinants of plant community diversity and structure, environmental change, extinction, floristic tracking, taxonomic homogenization
Biology and Microbiology
30 Jan 2012 16:40 +0 (UTC)