Non-invasive optical physiological differential pathlength sensor
An optical physiological sensor configured to perform high speed spectral sweep analysis of sample tissue being measured to non-invasively predict an analyte level of a patient. An emitter of the optical physiological sensor can be regulated to operate at different temperatures to emit radiation at different wavelengths. Variation in emitter drive current, duty cycle, and forward voltage can also be used to cause the emitter to emit a range of wavelengths. Informative spectral data can be obtained during the sweeping of specific wavelength regions of sample tissue.
1. A method of measuring a blood or interstitial fluid constituent of a patient by varying light emitted in a physiological optical sensor, the method comprising:
determining a temperature, a drive current, a forward voltage, and a duty cycle of a light emitter that emits light at a first wavelength;
varying at least one of the determined temperature, drive current, forward voltage, and duty cycle of the emitter to cause the emitter to sweep through a range of wavelengths of light;
directing a first portion of the light emitted by the emitter to tissue of the patient and detecting, with a first detector, first attenuated light comprising the first portion of the emitted light over the swept range of wavelengths after attenuation through the tissue of the patient, wherein the first detector is configured to output a first plurality of signals corresponding to the detected, first attenuated light;
directing a second portion of the light emitted by the emitter to a second detector without attenuation through the tissue of the patient and detecting, with the second detector, second attenuated light comprising the second portion of the emitted light over the swept range of wavelengths, wherein the second detector is configured to output a second plurality of signals corresponding to the detected, second attenuated light,
wherein the emitter and the first detector are movable relative to each other and the emitter and the second detector are moveable relative to each other, and
wherein a thickness of the tissue is controlled at least in part by a depth stop such that a first distance between the emitter and the first detector is fixed to define a first known path length and a second distance between the emitter and the second detector is fixed to define a second known path length;
receiving and processing the first and second plurality of signals with a data collection device;
determining a plurality of bulk absorbance values based on the received and processed first and second plurality of signals from the first and second detectors, each of the plurality of bulk absorbance values indicative of an amount of light absorbed by the tissue of the patient;
determining a plurality of tissue absorption segments based on the plurality of bulk absorbance values determined from the first and second plurality of signals outputted by the first and second detectors over the range of wavelengths swept by the emitter; and
combining the plurality of tissue absorption segments to form a plurality of tissue absorption bands and generate at least a portion of a tissue absorption profile.
2. The method of claim 1 , wherein varying the determined temperature of the emitter comprises using a circuitry-based temperature alteration device or a thermal controller.
3. The method of claim 2 , wherein the circuitry-based temperature alteration device or the thermal controller comprises a Peltier device.
4. The method of claim 2 , wherein the circuitry-based temperature alteration device or the thermal controller comprises a temperature sensor, a thermoelectric cooler, and a heat sink.
5. The method of claim 1 , further comprising controlling a temperature of the first detector with a thermal controller.
6. The method of claim 1 , wherein varying the determined temperature of the emitter comprises controlling a thermal controller thermally coupled to the emitter with the data collection device.
7. The method of claim 1 , wherein the range of wavelengths spans from 1300 nm to 1650 nm.
8. The method of claim 1 , further comprising determining a slope of an absorption curve.
9. The method of claim 1 , further comprising determining at least one physiological parameter of the patient based on at least the portion of the tissue absorption profile.
10. The method of claim 1 , wherein the first detector is optically shielded.
11. The method of claim 1 , wherein the steps of directing the first portion of the light emitted by the emitter to the tissue of the patient and directing the second portion of the light emitted by the emitter to the second detector are performed by a splitter.
12. The method of claim 1 , wherein the first portion of the emitted light is greater than the second portion of the emitted light.
13. The method of claim 1 , further comprising directing a third portion of the light emitted by the emitter to a reference absorption material and detecting, with a third detector, the third portion of the emitted light over the swept range of wavelengths after the third portion of light passes through the reference absorption material, wherein the third detector is configured to output a third plurality of signals corresponding to the detected, third portion of light.
14. The method of claim 1 , wherein the range of wavelengths swept through by the emitter comprises more than three wavelengths.
15. The method of claim 1 , wherein the first distance is greater than the second distance.
16. An optical physiological measurement system comprising:
an emitter configured to emit light at a first wavelength;
at least one of:
a first thermal controller coupled to the emitter and configured to vary an operation temperature of the emitter to cause the emitter to sweep through a range of wavelengths; and
a driver configured to vary a current delivered to the emitter to cause the emitter to sweep through the range of wavelengths;
a splitter configured to receive the light emitted from the emitter and split the light into a first portion and a second portion, the splitter further configured to direct the first portion towards a first detector without attenuation through tissue of a patient and direct the second portion towards the tissue;
the first detector, the first detector configured to detect the first portion of light emitted by the emitter as the emitter is swept through the range of wavelengths and output signals responsive to the detected light;
a second detector configured to detect second attenuated light comprising the second portion of light emitted by the emitter after attenuation through the tissue of the patient as the emitter is swept through the range of wavelengths, the second detector further configured to output signals responsive to the detected, second attenuated light;
a third detector configured to detect reference attenuated light comprising a third portion of light emitted by the emitter after attenuation through a first aqueous reference material having a known absorption profile as the emitter is swept through the range of wavelengths, the third detector further configured to output signals responsive to the detected, reference attenuated light;
wherein a thickness of the tissue is controlled at least in part by a depth stop such that a first distance between the emitter and the first detector is fixed to define a first known path length and a second distance between the emitter and the second detector is fixed to define a second known path length;
a data collection device configured to receive and convert the output signals from the first, second, and third detectors from an analog form to a digital form; and
a temperature sensor configured to monitor a temperature of the first reference material;
a signal processor in communication with the data collection device, the signal processor configured to receive and process the converted, digital output signals from the data collection device, wherein the signal processor is further configured to:
determine a plurality of bulk absorbance values based on the received and processed output signals from the first, second, and third detectors, each of the plurality of bulk absorbance values indicative of an amount of light absorbed by the tissue of the patient;
determine a plurality of tissue absorption segments based on the plurality of bulk absorbance values determined from the output signals of the first, second, and third detectors over the range of wavelengths swept by the emitter and the temperature of the first reference material; and
combine the plurality of tissue absorption segments to form a plurality of tissue absorption bands and generate at least a portion of a tissue absorption profile.
17. The optical physiological measurement system of claim 16 , wherein the range of wavelengths spans from 1300 nm to 1650 nm.
18. The optical physiological measurement system of claim 16 , wherein the signal processor is further configured to determine at least one physiological parameter of the patient based on the at least the portion of the tissue absorption profile.
19. The optical physiological measurement system of claim 16 , wherein the second detector is coupled to a second thermal controller, the second thermal controller configured to control a temperature of the second detector.
20. The optical physiological measurement system of claim 16 , wherein the data collection device is configured to control the first thermal controller to vary the operation temperature of the emitter.