In vivo blood spectrometry

Abstract

A process and apparatus for determining the arterial and venous oxygenation of blood in vivo with improved precision. The optical properties of tissue are measured by determination of differential and total attenuations of light at a set of wavelengths. By choosing distinct wavelengths and using the measured attenuations, the influence of variables such as light scattering, absorption and other optical tissue properties is canceled out or minimized.

1 - 25 . (canceled) 
     
     
         26 . An apparatus for measuring tissue oxygenation comprising:
 a sensor interface including at least one emitter configured to emit light into tissue with at least three wavelengths and at least one detector configured to receive light scattered by the tissue; and   a processor coupled to the sensor interface and configured to calculate tissue oxygenation using the at least three wavelengths, the tissue oxygenation corresponding to venous blood oxygenation, the processor further configured to compensate for influence of varying optical tissue properties which are exponentially decreasing with increasing wavelength.   
     
     
         27 . The apparatus of  claim 26  wherein the processor is configured to read coded information corresponding to the sensor interface and configured to use the coded information in calculating tissue oxygenation. 
     
     
         28 . An apparatus comprising:
 a sensor interface configured for coupling to a forehead of a person, the sensor interface including at least one light emitter configured to emit at least three different wavelengths of light into tissue, the sensor interface including at least two detectors configured to detect scattered light, the sensor interface having an emitter-detector distance of at least 2 cm;   a processor coupled to the sensor interface and configured to calculate at least two light attenuations LAwsj which depend on detected light for selected wavelength wsj for the at least two detectors; and   a display device coupled to the processor and configured for displaying tissue oxygenation corresponding to venous blood and for displaying arterial blood oxygenation based on pulse oximetry, the tissue oxygenation based on the least two light attenuations LAwsj.   
     
     
         29 . The apparatus of  claim 28  wherein the processor is configured to compensate for influence of varying optical tissue properties which are exponentially decreasing with increasing wavelength, and wherein the sensor interface includes an electrode configured for contacting a skin of the person, and wherein the sensor interface is coupled to an encoder, the encoder configured to store coded information about a wavelength of the sensor interface and configured to store the emitter-detector distance. 
     
     
         30 . The apparatus of  claim 28  wherein the at least one light emitter includes an LED and a demultiplexer, wherein an emitter timing is controlled by the demultiplexer. 
     
     
         31 . The apparatus of  claim 28  wherein the display device is configured to display a value that corresponds to oxygen extraction based on arterial oxygenation and venous oxygenation. 
     
     
         32 . The apparatus of  claim 28  in which at least one light emitter emits at about 660 nm. 
     
     
         33 . The apparatus of  claim 28  wherein the processor is configured to determine arterial blood oxygenation based on at least one light path between the at least one light emitter and one of the at least two detectors, wherein the at least one light path is less than 2 cm. 
     
     
         34 . The apparatus of  claim 28  wherein the at least one light emitter emits light at wavelengths of about wb1=740 nm and wb2=805 nm. 
     
     
         35 . The apparatus of  claim 28  wherein the at least one light emitter emits light at a wavelength of about wb3=660 nm. 
     
     
         36 . The apparatus of  claim 28  wherein the at least one light emitter include an LED configured to emit light into the tissue. 
     
     
         37 . The apparatus of  claim 28  wherein the light attenuations LAwsj are configured to reduce the dependency of the output for tissue oxygenation on Hb and blood content. 
     
     
         38 . The apparatus of  claim 28  wherein the processor is configured to calculate a value corresponding to a difference of arterial blood oxygenation and tissue oxygenation. 
     
     
         39 . The apparatus of  claim 28  wherein the display device is configured to display a pulse rate. 
     
     
         40 . The apparatus of  claim 28  wherein the display device is configured to display a blood constituent including carboxyhemoglobin, methemoglobin, glucose in blood, Hb, SvO2, SaO2, or bilirubin. 
     
     
         41 . An apparatus for measuring tissue oxygenation comprising:
 a sensor interface adapted to be coupled to the forehead of a person and including at least one light emitter and configured to emit light into tissue at at least three different wavelengths and having at least two detectors configured for detecting scattered light, wherein a detector-emitter distance is at least 2 cm, the sensor interface having an electrode configured for contacting a skin of the person;   a processor coupled to the sensor interface and configured to calculate at least two light attenuations LAwsj which depend on detected light for selected wavelength wsj for the two detectors; and   a display device coupled to the processor and configured for displaying an output for tissue oxygenation corresponding to venous blood, the output based on the light attenuations LAwsj.   
     
     
         42 . The apparatus of  claim 41  wherein the electrode is configured to detect an electrocardiogram (ECG) signal. 
     
     
         43 . The apparatus of  claim 41  wherein the sensor interface is configured for fixation to the forehead using medical glue, a fixation band, and a disposable sensor holder. 
     
     
         44 . An apparatus for measuring tissue oxygenation comprising:
 a sensor interface including at least one emitter and at least one detector, the at least one emitter configured to emit light into tissue with at least three wavelengths and the at least one detector to receive light scattered by the tissue;   a processor configured to calculate tissue oxygenation corresponding to venous oxygenation;   a sensor encoder configured to store coded information about a wavelength of the sensor interface; and   wherein the processor is configured to reduce an error associated with varying sensor hardware.   
     
     
         45 . The apparatus of  claim 44  wherein the sensor encoder is configured to store coded information about calibration of sensor geometry. 
     
     
         46 . An apparatus for measuring tissue oxygenation comprising:
 a sensor interface including at least one emitter configured to emit light into tissue with at least three wavelengths and at least one detector to receive light scattered by the tissue;   a processor configured to calculate tissue oxygenation corresponding to venous oxygenation;   a sensor encoder configured to store coded information about calibration of sensor geometry; and   wherein the processor is configured to reduce an error associated with varying sensor hardware.