Physiological metric estimation rise and fall limiting
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Publication Number
US-11350884-B2
Publication Date
2022-06-07
Expiration Date
Abstract
Methods and apparatus disclosed herein use a filtering technique to improve the accuracy of the results achieved when processing data provided by a physiological sensor. The disclosed filtering technique corrects many of the accuracy problems associated with physiological sensors, particularly PPG sensors. Broadly, the filtering technique adjusts a current filtered estimate of a physiological metric as a function of a rate limit based on a comparison between an instantaneous estimate of the physiological metric and the current filtered estimate.
Core Innovation
The invention describes a physiological processor disposed in a device secured to a body of a user, where the physiological processor processes a time domain photoplethysmography waveform provided by a photoplethysmography sensor disposed in the device and in contact with skin of the user. The physiological processor includes a spectral transformer configured to convert the photoplethysmography waveform from the time domain to a frequency domain to generate a spectrum, and to identify a first spectral peak having a largest magnitude in the spectrum and a second spectral peak having a next largest magnitude in the spectrum. The spectral transformer determines, responsive to the spectrum, an instantaneous estimate of a heart rate or another physiological metric.
The physiological processor further includes a filter operatively connected to the spectral transformer and configured to compare the instantaneous estimate to a current filtered estimate of the physiological metric. The filter determines a rising rate limit or a falling rate limit depending respectively on whether the instantaneous estimate is larger or smaller than the current filtered estimate. The rising rate limit or falling rate limit is determined relative to the current filtered estimate as a function of the first spectral peak and the second spectral peak.
Using the rising rate limit or falling rate limit, the filter computes a revised filtered estimate of the physiological metric based on whether the instantaneous estimate is greater than or equal to the current filtered estimate or is less than the current filtered estimate. The revised filtered estimate is then output, to an output interface, as a heart rate or the other physiological metric. The approach is described as using spectral peak information to constrain changes in the filtered estimate through rising and falling rate limits, including conditional update behaviors.
Claims Coverage
The document provides three independent claims: clm-00001 (physiological processor), clm-00007 (method), and clm-00023 (physiological processor). Across these independent claims, the core claim coverage centers on four inventive features: spectral transformer conversion and peak-based instantaneous estimation, rate-limit-based filtering using rising and falling limits, conditional revised filtered estimate computation, and output of the revised filtered estimate via an output interface.
Spectrum-based instantaneous physiological-metric estimate using first and second spectral peaks
A spectral transformer converts the time domain photoplethysmography waveform from the time domain to a frequency domain to generate a spectrum; identifies a first spectral peak having a largest magnitude and a second spectral peak having a next largest magnitude; and determines, responsive to the spectrum, an instantaneous estimate of a heart rate (or other physiological metric).
Rising and falling rate limits determined from the first and second spectral peaks
A filter compares the instantaneous estimate to a current filtered estimate and determines a rising rate limit or a falling rate limit depending respectively on whether the instantaneous estimate is larger or smaller than the current filtered estimate, wherein the rising rate limit or falling rate limit is determined relative to the current filtered estimate as a function of the first spectral peak and the second spectral peak.
Conditional revised filtered estimate based on whether instantaneous estimate is above or below current filtered estimate
The filter computes a revised filtered estimate of the physiological metric as a function of the rising rate limit when the instantaneous estimate is greater than or equal to the current filtered estimate, and as a function of the falling rate limit when the instantaneous estimate is less than the current filtered estimate.
Output of the revised filtered estimate
The physiological processor outputs, to an output interface, the revised filtered estimate of the heart rate (or the physiological metric) or the method outputs the revised filtered estimate to an output interface.
The independent claims consistently require (i) converting the time domain physiological waveform to a frequency domain spectrum, (ii) identifying a largest-magnitude first spectral peak and a next-largest-magnitude second spectral peak to determine an instantaneous estimate of a physiological metric, (iii) comparing the instantaneous estimate to a current filtered estimate and applying rising vs falling rate limits determined as a function of the two spectral peaks, and (iv) computing and outputting a revised filtered estimate via conditional functions.
Stated Advantages
Documented Applications
Not explicitly described in patent.
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