As is known, one blood constituent measuring device is an oximeter uses a photoelectric photometer to measure the fraction of hemoglobin in the blood which is in the form of oxygenated Hb. This oxygenated Hb fraction is generally referred to as a percentage where the percentage value is used to referred to the oxygen saturation of the blood.
Various oximeter devices and methods have been developed in the past. Some examples are disclosed in U.S. Pat. Nos. 4,407,290; 4,265,554; 4,167,331; 4,086,915; and 3,998,550, the disclosures of which are incorporated herein by reference. While oximetry devices and/or methods have heretofore been suggested and/or utilized, none of these devices and/or methods have proven to be completely satisfactory, and improvements have therefore still been needed with respect to such devices and/or methods.
Many of the prior art devices and methods make use of a plurality of sequences of pulses of light of different wavelength. The amount of light transmitted through the tissue is detected by a photo cell which in turn emits an electrical signal which is amplified and saved for processing. In order to property separate the pulses in the stream of data the photocell amplifier must be able to quickly settle back to the initial measurement level between each pulse. In order to obtain settling time a relative broad band amplifier has been employed in the past. The use of the broad band amplifier has lead to some difficulties. The oximeters are often used in operating rooms in which there are a wide range of electromagnetic wave producing devices present which can result in signals which introduce interference signals which can cause the device to give improper results.
An object of the present invention is to provide a device which is less susceptible to being affected by extraneous electromagnetic waves that may be present.
Other aspects, objects, and advantages of the present invention will become apparent to those skilled in the art having had the benefit of the following disclosure and the accompanying drawings.