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Publication Number
US-10687742-B2
Publication Date
2020-06-23
Expiration Date
Abstract
An example method for performing pulse oximetry can commence with receiving at least three light signals of three different wavelengths reflected from a human tissue. The human tissue includes a pulsatile tissue and a non-pulsatile tissue. Based on the three light signals, values of at least three functions are determined. The three functions are invariant to an oxygen saturation in the pulsatile tissue and depend on location of a sensor operable to detect the three light signals and pressure of the sensor on the human tissue. Based on the values of the three functions, non-pulsatile components are analyzed for intensities of a red light signal and infrared light signal reflected from the human tissue. The non-pulsated components are removed from the intensities to allow correct estimates of a ratio of the absorption coefficients, with the ratio being used to determine the oxygen saturation in the pulsatile tissue.
Core Innovation
The invention performs pulse oximetry by receiving concurrent red light signal, infrared light signal, and a third light signal reflected from human tissue including pulsatile tissue and non-pulsatile tissue. The red light signal is associated with a red wavelength, the infrared light signal is associated with an infrared wavelength, and the third wavelength is different from the red wavelength and the infrared wavelength. The approach determines, from each of the three light signals, first, second, and third values of first, second, and third functions invariant to oxygen saturation in the pulsatile tissue.
Using the invariant function values, the invention determines additive components in the red light signal and in the infrared light signal. The first additive component and the second additive component are due to reflection from the non-pulsatile tissue, and the invention removes the first and second additive components from respective intensities to estimate first corrected intensity and second corrected intensity. The invention then calculates a ratio of a red light absorption coefficient and an infrared light absorption coefficient from the corrected intensities, and determines at least the oxygen saturation in the pulsatile tissue based at least partially on the ratio.
The invention further acquires a reference photoplethysmogram (PPG) waveform and determines similarity measures between a pre-determined number of waveforms of the red light signal and the reference PPG waveform, and between a pre-determined number of waveforms of the infrared light signal and the reference PPG waveform, with the red and infrared waveforms detected concurrently. An average of products of the similarity measures (Ai×Bi) is calculated to estimate adequacy of the red light signal and the infrared light signal, and the invention estimates the adequacy based on the average of products.
It collects data over time concerning the red light signal, the infrared light signal, the third light signal, the adequacy, and the oxygen saturation, analyzes the data to detect trends in the oxygen saturation, and provides reports regarding a health status of the patient based on the trends.
Claims Coverage
The independent claims are directed to three claim categories: a method, a system, and a non-transitory computer-readable storage medium. Across these independent claims, the inventive features include concurrent reflected red, infrared, and third-wavelength signals; oxygen-saturation-invariant function values; additive components due to non-pulsatile tissue reflection and their removal; a red/infrared absorption-coefficient ratio for oxygen-saturation estimation; signal adequacy using similarity measures against a reference PPG waveform; and trend analysis of oxygen saturation for health-status reports.
Concurrent reflected red, infrared, and third-wavelength signals from pulsatile and non-pulsatile tissue
Receiving a red light signal reflected from human tissue of the patient including a pulsatile tissue and a non-pulsatile tissue, an infrared light signal reflected from the human tissue including a pulsatile tissue and a non-pulsatile tissue, and a third light signal reflected from the human tissue, each associated with its wavelength, with the third wavelength being different from the red wavelength and the infrared wavelength.
Oxygen-saturation-invariant function values from each wavelength channel
Determining first, second, and third values of first, second, and third functions invariant to an oxygen saturation in the pulsatile tissue based on the red light signal, the infrared light signal, and the third light signal, respectively.
Non-pulsatile reflection additive components removal for corrected intensities
Determining a first additive component in the red light signal and a second additive component in the infrared light signal based on the first, second, and third invariant function values, wherein the additive components are due to reflection from the non-pulsatile tissue; removing the additive components from the intensities to estimate corrected intensities.
Corrected intensity red/infrared absorption coefficient ratio for SpO2
Calculating, based on the first corrected intensity and the second corrected intensity, a ratio of a red light absorption coefficient and an infrared light absorption coefficient, and determining at least the oxygen saturation in the pulsatile tissue based at least partially on the ratio.
Signal adequacy using reference PPG waveform similarity measures
Acquiring a reference photoplethysmogram (PPG) waveform; determining first similarity measures between a pre-determined number of waveforms of the red light signal and the reference PPG waveform and second similarity measures between a pre-determined number of waveforms of the infrared light signal and the reference PPG waveform, with the red and infrared waveforms detected concurrently; calculating an average of products Ai×Bi to estimate adequacy of the red light signal and the infrared light signal, where Ai are the first similarity measures and Bi are the second similarity measures.
Trend analysis of oxygen saturation and provision of health-status reports
Collecting data over a period of time concerning the red light signal, the infrared light signal, the third light signal, the adequacy, and the oxygen saturation; analyzing the data to detect trends in the oxygen saturation; and providing reports regarding a health status of the patient based on the trends in the oxygen saturation.
The independent claims cover a pulse oximetry approach that computes oxygen saturation from concurrent reflected red, infrared, and a third wavelength channel by using oxygen-saturation-invariant function values, removing additive components due to non-pulsatile tissue reflection, and calculating a corrected red/infrared absorption-coefficient ratio. They also cover adequacy estimation using similarity measures against a reference PPG waveform, followed by collecting time-series data, detecting trends in oxygen saturation, and providing health-status reports.
Stated Advantages
Enables estimating oxygen saturation in pulsatile tissue by correcting for additive components due to reflection from non-pulsatile tissue.
Provides an adequacy estimate of the red light signal and the infrared light signal based on waveform similarity to a reference PPG waveform.
Detects trends in oxygen saturation over time and provides reports regarding a health status of the patient.
Documented Applications
Pulse oximetry for estimating oxygen saturation in pulsatile tissue and providing health-status reports for a patient.
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