The present invention relates to a biosensing system and method for monitoring internal physiological conditions of a patient. More particularly, the present invention relates to a biosensor system implantable in a patient""s body that includes at least one sensor, an active acoustic transducer and a miniature processor. The sensor is used to monitor a physiological condition of the patient and relay information pertaining to the physiological condition through the miniature processor to the active acoustic transducer. The active acoustic transducer transmits this information out of the patient""s body as an acoustic signal. Transmission of an acoustic signal from the transducer is triggered by an externally generated acoustic interrogation and energizing signal, which is produced by a second acoustic transducer positioned externally, yet in intimate contact with, the patient""s body. The miniature electronic processor is utilized for the various required functions such as conditioning, digitization and amplification of the sensor signals. The biosensor of the present invention can also include a shunt and a monitoring device embedded in the walls of the shunt for permitting identification and non-invasive testing of the operation of the shunt via the acoustic transducer.
Many medical conditions require the monitoring and measurement of internal physiological conditions of a patient. For example, hydrocephalus, which is a brain condition where cerebrospinal fluid accumulates at abnormally high pressures in ventricles or chambers of a patient""s brain, may require monitoring of the intra-cranial fluid pressure of the patient.
Implantable devices for monitoring internal physiological conditions of a patient are known in the art. One such prior art device includes an implantable pressure sensor that transmits pressure signals out of the patient by mechanism of a wire or contact passing through the patient""s skull (see, for example, U.S. Pat. No. 4,677,985). These types of devices are generally unsatisfactory due to increased risk of infection and patient discomfort caused by the externally extending wire.
Monitoring devices that are completely implantable within a patient are also known in the art. One such prior art devices is described in U.S. Pat. No. 4,471,786 and includes a sensor for sensing a physiological condition of the patient and a transmitter and battery assembly for transmitting the sensor signals out of the patient""s body. These types of devices are also unsatisfactory for many types of medical conditions since the batteries are bulky and must be periodically replaced, thus necessitating additional surgery.
Implantable monitoring devices that do not require batteries have also been developed. Such devices (see, for example, U.S. Pat. Nos. 3,943,915 and 4,593,703) employ sensors coupled with frequency tuned Lumped-Constant (L-C) circuits. The sensors mechanically translate changes in sensed physiological condition to the inductor or capacitor of the tuned L-C circuit for changing the reactance of the L-C circuit. This change in reactance alters the resonant frequency of the circuit, which is then detected by an external receiver and converted to a signal representative of the monitored physiological condition.
Although these L-C type implantable monitoring devices are superior to battery operated devices in some respects, they also suffer from several limitations that limit their utility. For example, the L-C circuits are difficult to calibrate once implanted, are inherently single-channel, and are only sensitive in a particular range of measurements. Thus, L-C type monitoring devices are not always accurate after they have been implanted for a long period of time and are not suitable for use with sensors that have a wide sensing range. In addition, no processing power is provided.
Another implantable monitoring device that does not utilizes wire connection or a battery supply makes use of large electromagnetic antennae to provide the energy required for the data processing inside the body. These antennas are big and risky to implant. Also, due to the high absorption of electromagnetic energy by human tissue, only subcutaneous implants are used, and energy into the depth of the body is realized by wiring coupling. Only small amounts of electromagnetic energy can be transmitted from an external antenna directly to a monitoring device deep in the body.
A general limitation of all of the above-described prior art implantable monitoring devices is that they are operable for sensing or monitoring only one physiological condition. Thus, if a doctor wishes to monitor, e.g., both the pressure and the temperature of the fluid in the ventricles of a patient""s brain, two such devices must be implanted.
Furthermore, these prior art implantable devices merely monitor a physiological condition of the patient and transmit a signal representative of the condition out of the patient""s body, but do not perform any processing or conversion of the signals.
In addition, due to inherent design limitations, these devices cannot be utilized for alleviating the underlying cause of the physiological condition monitored. For example, intra-cranial pressure sensors designed for use with patients suffering from hydrocephalus merely detect when fluid pressure levels within the patient""s brain are high, but are not operable for reducing the amount of cerebrospinal fluid accumulated in the patient""s brain. Thus, once these prior intra-cranial pressure sensors determine that the pressure in the patient""s brain is too high, surgery must be performed to alleviate the condition.
An improved implantable biosensor for monitoring and alleviating internal physiological condition such as intracranial pressure has been described in U.S. Pat. No. 5,704,352 which discloses a biosensor system which includes at least one sensor for monitoring a physiological condition of the patient and a passive radio frequency transducer that receives sensor signals from the sensor or sensors, digitizes the sensor signals, and transmits the digitized signals out of the patient""s body when subjected to an externally generated electromagnetically interrogation and energizing signal. The biosensor system described also includes a shunt, and as such it can be used for alleviating intracranial pressure monitored by the sensors of the biosensor.
Although this biosensor system presents a major advance over the above mentioned prior art devices and systems, it suffers from limitations inherent to the radio frequency transducer utilized thereby. Since this transducer requires the use of an antenna to receive and transmit signals, it posses limited reception and transmission capabilities due to the directional nature of such antennas. In addition, due to the high absorption of electromagnetic energy by human tissue, deeply embedded implants cannot be realized by this system and as a result, the intra body positioning of such a biosensor is limited to regions close to the skin which are accessible to electromagnetic signals, thus greatly limiting the effectiveness of such a system.
There is thus a widely recognized need for, and it would be highly advantageous to have, a biosensor system for monitoring and alleviating internal physiological conditions, such as intra-cranial pressure, devoid of the above limitations.
It is therefore an object of the present invention to provide a biosensor which can be used for non-invasive monitoring of body parameters.
It is another object of the present invention to provide such a biosensor which does not require wiring or an integral power source.
It is yet another object of the present invention to provide a biosensor which is less sensitive to extracorporeal positional effect when energized as compared to prior art devices.
It is still another object of the present invention to provide a biosensor which is effectively operable from any depth within the body.
To realize and reduce down to practice these objectives, the biosensor according to the present invention takes advantage of the reliable conductivity of acoustic radiation within water bodies, such as a human body and of an acoustic activatable piezoelectric transducer. According to one aspect of the present invention there is provided
According to one aspect of the present invention there is provided an implantable biosensor system for monitoring and optionally alleviating a physiological condition in a patient, the biosensor system comprising (a) at least one sensor for sensing at least one parameter of a physiological condition and for generating electrical sensor signals representative of the physiological condition; and (b) a first acoustic activatable transducer being directly or indirectly coupled with the at least one sensor, the first acoustic activatable transducer being for converting a received acoustic interrogation signal from outside the patient""s body into an electrical power for energizing the processor, the first acoustic activatable transducer further being for converting the electrical sensor signals of the at least one sensor into acoustic signals receivable out of the patient""s body, such that information pertaining to the at least one parameter of the physiological condition can be relayed outside the patient""s body upon generation of an acoustic interrogation signal.
According to further features in preferred embodiments of the invention described below, the biosensor system further comprising a processor coupling between the at least one sensor and the first acoustic activatable transducer, the processor being for converting the electrical sensor signals into converted electrical signals representative of the physiological condition, the processor being energized via the electrical power.
According to another aspect of the present invention there is provided an implantable biosensor system for monitoring and alleviating a physiological condition in a patient, the biosensor system comprising (a) a shunt having a fluid passageway and being operable for draining fluid through the fluid passageway from a portion of a patient""s body; (b) a monitoring and operating mechanism coupled with the shunt for non-invasively monitoring the physiological condition and operating the shunt, the monitoring and operating mechanism including at least one sensor for sensing at least one parameter of the physiological condition and for generating electrical sensor signals representative of the physiological condition; and (c) a first acoustic activatable transducer being directly or indirectly coupled with the at least one sensor, the first acoustic activatable transducer being for converting a received acoustic interrogation signal from outside the patient""s body into an electrical power for energizing the at least one sensor and for operating the shunt upon command, the first acoustic activatable transducer further being for converting the electrical sensor signals into acoustic signals receivable out of the patient""s body, such that information pertaining to the at least one parameter of the physiological condition can be relayed outside the patient""s body upon generation of an acoustic interrogation signal and the shunt is operable upon command.
According to still further features in the described preferred embodiments the monitoring and operating mechanism further includes a processor coupled with the at least one sensor, the processor serves for converting the electrical sensor signals to converted electrical signals representative of the physiological condition.
According to still further features in the described preferred embodiments the command is an acoustic operation signal provided from outside the body.
According to still further features in the described preferred embodiments the shunt is a cerebrospinal fluid shunt for draining cerebrospinal fluid from the patient""s brain.
According to still further features in the described preferred embodiments the at least one sensor includes a first pressure sensor positioned within the fluid passageway for sensing the pressure of the cerebrospinal fluid in the patient""s brain and for generating a first pressure signal representative of that pressure.
According to still further features in the described preferred embodiments the at least one pressure sensor includes a second pressure sensor positioned at a distance from the first pressure sensor and being for sensing the pressure of the cerebrospinal fluid when flowing through the shunt and for generating a second pressure signal representative of that pressure.
According to still further features in the described preferred embodiments the processor receives the first and second pressure signals from the first and second pressure sensors and calculates the flow rate of cerebrospinal fluid through the shunt.
According to still further features in the described preferred embodiments the first acoustic activatable transducer includes (i) a cell member having a cavity; (ii) a substantially flexible piezoelectric layer attached to the cell member, the piezoelectric layer having an external surface and an internal surface, the piezoelectric layer featuring such dimensions so as to enable fluctuations thereof at its resonance frequency upon impinging of the acoustic interrogation signal; and (iii) a first electrode attached to the external surface and a second electrode attached to the internal surface.
According to still further features in the described preferred embodiments the piezoelectric layer is of a material selected from the group consisting of PVDF and piezoceramic.
According to still further features in the described preferred embodiments the processor includes a conditioner and a digitizer for converting the electrical sensor signal to the converted electrical signal.
According to still further features in the described preferred embodiments the converted electrical signal is a digital signal.
According to still further features in the described preferred embodiments the processor, the first acoustic activatable transducer and the at least one sensor are co-integrated into a single biosensor device.
According to still further features in the described preferred embodiments the biosensor system further comprising (c) an extracorporeal station positionable against the patient""s body the extracorporeal station including an interrogation signal generator for generating the acoustic interrogation signal, the interrogation signal generator including at least one second transducer for transmitting the interrogation signal to the first acoustic activatable transducer and for receiving the receivable acoustic signals from the first acoustic activatable transducer.
According to still further features in the described preferred embodiments the processor includes a memory device for storing the electrical sensor signals and an analyzer for analyzing the electrical sensor signals.
According to still further features in the described preferred embodiments the processor includes a programmable microprocessor.
According to still further features in the described preferred embodiments the at least one sensor is selected from the group consisting of a pressure sensor, a temperature sensor, a pH sensor, a blood sugar sensor, a blood oxygen sensor, a motion sensor, a flow sensor, a velocity sensor, an acceleration sensor, a force sensor, a strain sensor, an acoustics sensor, a moisture sensor, an osmolarity sensor, a light sensor, a turbidity sensor, a radiation sensor, an electromagnetic field sensor, a chemical sensor, an ionic sensor, and an enzymatic sensor.
According to still further features in the described preferred embodiments the first acoustic activatable transducer is capable of transmitting an identification code identifying the transducer.
According to yet another aspect of the present invention there is provided a method for non-invasive monitoring of a physiological condition within a patient""s body, the method comprising the steps of (a) sensing at least one parameter associated with the physiological condition via at least one sensor implanted within the patient""s body to thereby obtain information pertaining to the physiological condition as an electrical output; (b) converting the electrical output into an acoustic signal via an acoustic transducer and thereby acoustically relaying the information to outside the patient""s body; and (c) relaying an acoustic interrogation signal from outside the patient""s body for activating the at least one sensor.
According to still another aspect of the present invention there is provided a method for non-invasive monitoring and alleviating of a physiological condition within a patient""s body, the method comprising the steps of (a) sensing at least one parameter associated with the physiological condition via at least one sensor implanted within the patient""s body to thereby obtain information pertaining to the physiological condition as an electrical output; (b) converting the electrical output into an acoustic signal via an acoustic transducer and thereby acoustically relaying the information to outside the patient""s body; and (c) relaying an acoustic interrogation signal from outside the patient""s body for activating the at least one sensor and further for activating a shunt for alleviating the physiological condition.
The present invention successfully addresses the shortcomings of the presently known configurations by providing a biosensor which can be used for non-invasive monitoring of body parameters, which does not require wiring, which does not require an integral power source, which can be effectively positioned at any location and depth within the body and which is much less subject to interrogation positional effect as compared with prior art devices.