Motion compatible sensor for non-invasive optical blood analysis

Abstract

A non-invasive optical sensor which uses the motion signal to calculate the physiological characteristic being measured. For pulse oximetry, a least squares or a ratio-of-ratios technique can be applied to the motion signal itself. This is made possible by selecting a site on the patient where variations in motion produce signals of two wavelengths which are sufficiently correlated. In particular, it has been determined that a sensor placed on a nail, in particular a thumbnail, exhibits the characteristics of having the red and infrared signals correlated when used for pulse oximetry, and the resulting signals correlate to arterial oxygen saturation.

1 . An optical sensor comprising: 
 a sensor body configured to attach to a patient;    an light emitter recessed in the sensor body; and    a light detector recessed in the sensor body and spaced apart from the light emitter.    
     
     
         2 . The optical sensor defined in  claim 1 , wherein the sensor comprises a pulse oximetry sensor.  
     
     
         3 . The optical sensor defined in  claim 1 , wherein the sensor is configured to attach to a patient's digit over a nail, and wherein the light emitter and the light detector are configured to be mounted adjacent to the nail.  
     
     
         4 . The optical sensor defined in  claim 1 , wherein the sensor is a reflectance sensor.  
     
     
         5 . The optical sensor defined in  claim 1 , wherein at least one of the light emitter or the light detector has a numerical aperture of less than 0.9.  
     
     
         6 . The optical sensor defined in  claim 1 , wherein at least one of the light emitter or the light detector has a numerical aperture of less than 0.5.  
     
     
         7 . The optical sensor defined in  claim 1 , comprising a display disposed on the sensor for displaying at least one of a blood oxygen saturation value or a pulse rate.  
     
     
         8 . The optical sensor defined in  claim 7 , wherein the light emitter, the light detector, and the display are located in one housing of the sensor body.  
     
     
         9 . The optical sensor defined in  claim 7 , comprising a button or switch for alternating between displaying the pulse rate and the oxygen saturation value.  
     
     
         10 . A method of reducing light shunting in an optical sensor, comprising: 
 emitting light into a tissue by using an emitter recessed in a sensor body;    detecting the light from the tissue with a detector recessed in the sensor body, the detector being spaced apart from the emitter; and    generating a signal based on the detected light.    
     
     
         11 . The method of  claim 10 , comprising determining a blood oxygen saturation value from the signal.  
     
     
         12 . The method of  claim 10 , comprising displaying the blood oxygen saturation value on a display located on the sensor body.  
     
     
         13 . An pulse oximetry system comprising: 
 a sensor configured to attach to a patient, the sensor having a light emitter recessed in a sensor body and a light detector recessed in the sensor body, the light detector spaced apart from the light emitter; and    a pulse oximetry monitor operatively connected to the sensor.    
     
     
         14 . The pulse oximetry system defined in  claim 13 , wherein the sensor is configured to attach to a patient's digit over a nail, and wherein the light emitter and the light detector are configured to be mounted adjacent to the nail.  
     
     
         15 . The pulse oximetry system defined in  claim 13 , wherein the sensor comprises a reflectance sensor.  
     
     
         16 . The pulse oximetry system defined in  claim 13 , wherein at least one of the light emitter or the light detector has a numerical aperture of less than 0.9.  
     
     
         17 . The pulse oximetry system defined in  claim 13 , wherein at least one of the light emitter or the light detector has a numerical aperture of less than 0.5.  
     
     
         18 . The pulse oximetry system defined in  claim 13 , comprising a display disposed on the sensor for displaying a blood oxygen saturation value or a pulse rate.  
     
     
         19 . The pulse oximetry system defined in  claim 18 , wherein the light emitter, the light detector, and the display are located in one housing of the sensor body.  
     
     
         20 . The pulse oximetry system defined in  claim 18 , comprising a button or switch for alternating between displaying the pulse rate and the oxygen saturation value.