Systems and Methods for Measuring Oxygen in a Patient's Bloodstream

Abstract

A photometry device can include a first LED to emit light to a target in response to a first current through the first LED, a second LED to emit light to the target in response to a second current through the second LED, and an inductor, coupled to the first and second LEDs, to store energy associated with at least one of the first and second currents.

1 . A photometry method comprising:
 emitting light to at least a portion of a target using a variable amplitude current pulse to generate the emitted light;   determining an amount of charge used in the variable amplitude current pulse;   detecting light received from the at least a portion of the target in response to the emitted light; and   integrating a current associated with the received light in response to the emitted light.   
     
     
         2 . The photometry method of  claim 1 , comprising:
 determining a characteristic of the target using an indication of the integrated current and an indication of the amount of charge used in the variable amplitude current pulse.   
     
     
         3 . The photometry method of  claim 1 , comprising emitting light at different wavelengths and measuring a differential response to determine a composition characteristic of the target. 
     
     
         4 . The photometry method of  claim 1 , comprising collecting and storing the charge used in the variable amplitude current pulse. 
     
     
         5 . The photometry method of  claim 4 , comprising recycling the stored charge used in the variable amplitude current pulse to further emit light to the at least a portion of the target using an additional variable amplitude current pulse, detecting light received from the at least a portion of the target in response to the further emitted light, and integrating a current associated with the received light in response to the further emitted light. 
     
     
         6 . The photometry method of  claim 5 , comprising determining a characteristic of the target using an indication of the integrated current associated with the received light in response to the emitted light, an indication of charge used in the variable amplitude current pulse, an indication of the integrated current associated with the received light in response to the further emitted light, and an indication of charge used in the additional variable amplitude current pulse. 
     
     
         7 . A photometry device, comprising:
 a first LED to emit light to a target in response to a first current through the first LED;   a second LED to emit light to the target in response to a second current through the second LED; and   an inductor, coupled to the first and second LEDs, to store energy associated with at least one of the first and second currents.   
     
     
         8 . The device of  claim 7 , comprising a switch to selectively couple a terminal of the inductor to first and second reference voltage nodes. 
     
     
         9 . The device of  claim 8 , comprising a capacitor forming a tank circuit zith the inductor for storing energy. 
     
     
         10 . The device of  claim 9 , wherein charge is stored on the capacitor using the first current through the first LED, and wherein charge is discharged from the capacitor using the second current through the second LED. 
     
     
         11 . The device of  claim 9  comprising a photosensitive element to receive emitted light from the first LED and the second LED and integration circuitry to determine a charge corresponding to an amount of light received from the first LED and the second LED. 
     
     
         12 . The photometry device of  claim 11 , comprising control circuitry configured to determine a characteristic of the target using an indication of the charge corresponding to the amount of light received from the first LED and the second LED, and an indication of the charge stored on the first capacitor. 
     
     
         13 . A system for photometry of a target, the system comprising:
 a first light emitting element connected by a switching element to a first voltage source having a first voltage value, wherein the first light emitting element is configured to transmit light through at least a portion of the target;   a charge storage element configured to receive and store an amount of charge corresponding to a current delivered to the first light emitting element by the first voltage source; and   control circuitry configured to:
 determine a first potential across the charge storage element; 
 activate the switching element to connect the first voltage source to the first light emitting element; 
 determine a second potential across the charge storage element; and 
 determine an amount of charge stored on the charge storage element corresponding to an amount of light emitted by the first light emitting element from a difference between the second potential and the first potential. 
   
     
     
         14 . The system of  claim 13  comprising a photosensitive element configured to receive a portion of the light emitted by the first light emitting element and convert the received portion of light into an electrical signal, and integration circuitry configured to integrate the electrical signal to determine an amount of charge corresponding to the amount of light received. 
     
     
         15 . The system of  claim 14  wherein the control circuitry is configured to determine an amount of light absorbed by the portion of the target from a ratio of the amount of charge corresponding to an amount of light emitted by the first light emitting element and the amount of charge corresponding to the amount of light received. 
     
     
         16 . The system of  claim 15  comprising a second light emitting element connected by the switching element to a second voltage source having a second voltage value, wherein the second light emitting element is configured to transmit light through the portion of the target, and wherein the control circuitry is configured to activate the switching element to deliver the charge stored on the charge storage element as a second electrical current through the second light emitting element. 
     
     
         17 . The system of  claim 16  wherein the photosensitive element is configured to receive a portion of the light transmitted by the second light emitting element through the portion of the target. 
     
     
         18 . The system of  claim 17  wherein the control circuitry is configured to determine a third electrical potential across the charge storage element, and determine an amount of charge corresponding to an amount of light emitted by the second light emitting element from a difference between the third electrical potential and the second electrical potential. 
     
     
         19 . The system of  claim 18  wherein the control circuitry is configured to determine an amount of light absorbed by the portion of the target from a ratio of the amount of charge corresponding to an amount of light emitted by the second light emitting element and the amount of charge corresponding to the amount of light received from the second light emitting element. 
     
     
         20 . The system of  claim 18 , wherein a wavelength of the first light emitting element is different from a wavelength of the second light emitting element and a difference in light absorbed by the portion of the target between the first wavelength and the second wavelength is used to provide a measure of peripheral O 2  saturation. 
     
     
         21 . A photometry device, comprising:
 an LED to emit light to a target in response to a first current through the LED;   an inductor, coupled to the LED, to store energy associated with the first current; and   a capacitor forming a tank circuit with the inductor for storing energy.   
     
     
         22 . The device of  claim 21 , wherein charge is stored on the capacitor using the first current through the LED, and wherein charge is discharged from the capacitor to provide a second current through the LED. 
     
     
         23 . The device of  claim 21 , comprising a plurality of switches to reverse the polarity of the LED to allow the second current to flow from the capacitor and through the LED.