Techniques for accurately deriving physiologic parameters of a subject from photoplethysmographic measurements
First Claim
1. A method for deriving physiologic parameters of a subject from photoplethysmographic measurements comprising the steps of:
- Obtaining a frequency spectrum of a time-based photoplethysmograph of the subject;
Detecting a series of peaks of the frequency spectrum;
Calculating a change of frequency between adjacent detected peaks of the series of detected peaks of the frequency data set; and
Identifying a repeating change of frequency between adjacent detected peaks of the series of detected peaks of the frequency data set; and
Utilizing the identified repeating change of frequency to derive physiologic parameters of the subject.
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Abstract
Several techniques are disclosed for isolating either heart or breath rate data from a photoplethysmograph, which is a time domain signal such as from a pulse oximeter. The techniques involve the use of filtering in the frequency domain, after a Fast Fourier Transform (FFT) has been conducted on a given photoplethysmograph also references as a given set of discrete time-domain data. The filtering may be applied to an identified fundamental frequency and one or more harmonics for heart related parameters. The filter may be truncated to the frequency data set and further applied multiple times to improve roll off. After filtering, an Inverse FFT (IFFT) is used to reconstruct the time-domain signal, except with undesirable frequency content eliminated or reduced. Calculation or measurement of parameters is then conducted on this reconstructed time-domain signal.
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Citations
23 Claims
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1. A method for deriving physiologic parameters of a subject from photoplethysmographic measurements comprising the steps of:
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Obtaining a frequency spectrum of a time-based photoplethysmograph of the subject; Detecting a series of peaks of the frequency spectrum; Calculating a change of frequency between adjacent detected peaks of the series of detected peaks of the frequency data set; and Identifying a repeating change of frequency between adjacent detected peaks of the series of detected peaks of the frequency data set; and Utilizing the identified repeating change of frequency to derive physiologic parameters of the subject. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A method for deriving physiologic parameters of a subject from photoplethysmographic measurements comprising the steps of:
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Obtaining a frequency spectrum of a time-based photoplethysmograph of the subject; Detecting a series of peaks of the frequency spectrum; Filtering the frequency spectrum by applying a filter to the frequency spectrum in multiple passes; Obtaining a filtered time-based physiologic signal from the filtered frequency spectrum; and Calculating physiologic parameters from the filtered time-based physiologic signal.
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15. A method for deriving physiologic heart related parameters of a subject from photoplethysmographic measurements comprising the steps of:
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Obtaining a frequency spectrum of a time-based photoplethysmograph of the subject; Detecting a series of peaks of the frequency spectrum, wherein the physiologic parameters include heart rate and the detected peaks include a fundamental heart rate frequency and at least one harmonic of the fundamental heart rate frequency; Filtering the frequency spectrum to isolate the fundamental heart rate frequency and at least one harmonic of the heart rate frequency; Obtaining a filtered time-based physiologic heart signal from the filtered frequency spectrum; and Calculating physiologic parameters from the filtered time-based physiologic heart signal.
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16. A method for deriving physiologic parameters of a subject from photoplethysmographic measurements comprising the steps of:
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Obtaining a frequency spectrum of a time-based photoplethysmograph of the subject; Detecting at least one peak of the frequency spectrum; Determining a fundamental frequency whereby i) if more than one peak is detected then calculating a change of frequency between adjacent detected peaks of the series of detected peaks of the frequency spectrum and attempting to identify a repeating change of frequency between adjacent detected peaks of the series of detected peaks of the frequency spectrum, wherein the fundamental frequency is the repeating change of frequency, and ii) if only one peak is detected or if a change of frequency cannot be identified then identifying a maximum peak, wherein the maximum peak is the fundamental frequency; and Utilizing the fundamental frequency to derive physiologic parameters of the subject.
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17. A method for deriving physiologic parameters of a subject from photoplethysmographic measurements comprising the steps of:
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Obtaining a frequency spectrum of a time-based photoplethysmograph of the subject; Detecting a series of peaks of the frequency spectrum; Filtering the frequency spectrum by applying a windowed filter on the frequency data set; Obtaining a filtered time-based physiologic signal from the filtered frequency spectrum; and Calculating physiologic parameters from the filtered time based physiologic signal. - View Dependent Claims (18, 19, 20)
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21. A method for deriving physiologic parameters of a subject from photoplethysmographic measurements comprising the steps of:
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A) Obtaining a frequency spectrum of the time-based photoplethysmograph; B) Detecting a series of peaks of the frequency spectrum wherein the step of detecting a series of peaks of the frequency spectrum comprises the steps of i) providing a preset original threshold amplitude; ii) reviewing the frequency spectrum from high frequency to low frequency and identifying a first peak that crosses the preset original threshold amplitude value; iii) increasing the subsequent threshold amplitude; iv) reviewing the frequency data set from high frequency to low frequency from the last identified peak and identifying a second peak that crosses the subsequent threshold amplitude value; and C) Utilizing the identified peaks to derive physiologic parameters of the subject. - View Dependent Claims (22, 23)
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Specification