Abstract: A method and apparatus for non-invasively measuring blood constituent concentration and particularly the oxygen saturation of arterial blood. The apparatus includes at least one light source directed to a tissue area of a patient, such as a finger or earlobe. A photodetector receives emitted light passing through the sample, and a receiver circuit analyzes the data and produces an output which is proportional to the oxygen content of blood. The light source is modulated onto a preselected carrier frequency and the receiver circuit is tuned to the carrier frequency so that undesired signals such as ambient light can be filtered out leaving only the signals created by the emitted light passing through the tissue at the light source frequency. The oxygen content is then calculated using the patient's known red cell count, thereby correcting the final saturation value for patient anemia.

Abstract: A noncontact infrared tympanic thermometer which does not require environmental stabilization or waveguide temperature control because it utilizes an optically stabilized infrared detector for detecting the infrared energy emitted by the tympanic membrane. The optical stabilization renders the instrument insensitive to ambient temperature effects and allows it to read true tympanic membrane temperatures unaffected by the temperature of the side walls of the detector package. This selectivity is accomplished by locating a neutral density filter over half of the optical aperture of the detector package such that the neutral density filter "shadows" only one of two thermopile channels for detecting the infrared energy emitted by the tympanic membrane. The two thermopile channels are connected in series opposition such that any optical signal equally present in both channels will yield a zero net output.

Abstract: Method and apparatus for adapting the volumetric flow rate measurement system taught by Yelderman in U.S. Pat. No. 4,507,974 to clinical environments by reducing the effects of physiological noise. Signal processing techniques are used to characterize the background noise power spectrum of the system under test so that the effect of noise aberrations on the measured data may be eliminated and so that the predominant periodicities of the background noise spectra may be avoided. The invention further cross-correlates the input data of the system with the corresponding ouput data of the system to determine weighting values for each input frequency so that data collected at noisy frequencies is discounted. Low frequency noise or drift is also removed from the output signal by fitting the average of the output data to a quadratic function which is then subtracted from the original output signal, point by point.

Abstract: Methods and apparatus for constructing optically stabilized, shutterless infrared capnographs are disclosed. The capnographs of the present invention provide the absolute concentration of the constituents of the respiratory airstream of a patient, without the thermal drift problems normally associated with thermopile detectors, thereby providing a device with a high degree of accuracy. The present invention eliminates the need for a mechanical shutter to modulate the incident infrared beam and the need for a modulated source, thereby increasing the reliability and response time of the devices disclosed. Capnographs which are substantially unaffected by changes in the ambient temperature at which they operate are provided by connecting pairs of optically filtered thermopiles in series and processing the resulting differential pair.

Abstract: Improved infrared detectors for use in device such as capnographs are provided. A preferred embodiment of an infrared detector of the invention is comprised of paired thermopiles, connect in opposed relation to each other, which are preceded by an analytical or reference filter for passing a desired wavelength and a neutral density filter in the optical path of one of the thermopiles in the pair. The difference between the outputs can be used to eliminate the effects of background thermal noise, thereby improving performance of the detector. Preferably, a reference channel and an analytical channel are provided so that the respective differences between the detectors in each pair can be used to further cancel the effects of background thermal noise.

Abstract: A disposable endotracheal airway adapter for use in proximity of a patient's mouth in the measurement of the concentraton of respiratory gases. The disposable airway adapter of the invention provides a conduit for patient respiratory gases and allows the passage of infrared radiation through the gases for measuring the constituent concentration of the respiratory gases while keeping the patient gases from coming in contact with the analyzer mechanism. The body of the airway adapter is designed to connect in series with the airway tubing which connects a patient to a mechanical respirator or anesthesia breathing circuit. The body of the airway adapter is very light in weight and is formed of inexpensive material such as polyethylene or polypropylene so that it may be manufactured inexpensively and discarded after each use. An inexpensive optical window in the adapter is also formed of material such as polyethylene or polypropylene so that the gas analyzer can pass light into the sample for analysis.

Abstract: A sensor for trans-illumination of a blood perfused portion of flesh to measure light extinction during trans-illumination is disclosed. The sensor is preferably mounted on a fingertip but any digit or blood perfused portion of flesh will work. The sensor includes a first end for disposition on one side of the trans-illuminated flesh and a second end for disposition on the opposite and opposed side of the trans-illuminated flesh. A light source is mounted to the first side and a photo-sensor is mounted to the second side. If an elongated flexible strip is used, it is provided with adhesive and is suitably windowed that light is allowed to take an optical path through the finger. If no flexible strip is used, the two ends are aligned and secured to the flesh such that the light emitted takes an optical path through the finger.