METHOD AND APPARATUS FOR DETERMINING SpO2 OF A SUBJECT FROM AN OPTICAL MEASUREMENT
First Claim
1. A method of determining SpO2 of a subject from an optical measurement, the method comprising:
- (i) obtaining a first signal from a first light illumination;
(ii) obtaining a second signal from a second light illumination, the second light illumination having a wavelength which is different from that of the first light illumination;
(iii) pairing the first and second signals in which an amplitude of each cardiac rhythm cycle of the first signal is aligned to an amplitude of a respective cardiac rhythm cycle of the second signal to form a plurality of paired windows;
(iv) for each paired window, calculating values of a ratio R from the paired first and second signals;
(v) based on the calculated R values, binning the calculated R values into predetermined frequency bins; and
(vi) selecting at least one of the frequency bins to derive a revised ratio, Rrev; and
(vii) determining SpO2 from the revised ratio Rrev;
whereinthe method further comprises(viii) obtaining ACamb and DCamb;
(viiii) calculating a ratio, Ramb-signal, based on ACamb and ACsignal;
(x) providing a zoning schema divided into a plurality of reference zones with each reference zone defined by respective values of first, second and third reference variables which are associated respectively with Rrev, Ramb-signal and DCamb;
each reference zone being associated with a corresponding method of computing SpO2;
(xi) comparing Rrev, Ramb-signal and DCamb with respective reference variables of the zoning schema to determine which one of the plurality of reference zones is a selected zone; and
(xii) applying the method of computing SpO2 corresponding to the selected zone for determining SpO2;
whereACamb is an AC component value of an ambient signal with the first and second light illuminations switched off;
DCamb is a DC component value of the ambient signal; and
ACsignal is an AC component value of the first or second signal.
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Abstract
A method 100 and apparatus for determining SpO2, of a subject from an optical measurement is disclosed herein. In a described embodiment, the method 100 includes obtaining a PPG(red) signal and a PPG(IR) signal at steps 102 and 104, and pairing the PPG(red) and PPG(IR) signals at step 106 in which an amplitude of each cardiac rhythm cycle of the first signal is aligned to an amplitude of a respective cardiac rhythm cycle of the second signal to form a plurality of paired windows. At step 108, the method further includes, for each paired window, calculating values of a ratio R from the paired first and second signals and based on the calculated R values, binning the calculated R values into predetermined frequency bins at step 110. At steps 112 and 1 14, at least one of the frequency bins is selected to derive a revised ratio, Rrev and at step 1 16, Sp02 is derived from the revised ratio Rrev. A zoning schema for deriving SpO2 is also disclosed.
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Citations
26 Claims
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1. A method of determining SpO2 of a subject from an optical measurement, the method comprising:
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(i) obtaining a first signal from a first light illumination; (ii) obtaining a second signal from a second light illumination, the second light illumination having a wavelength which is different from that of the first light illumination; (iii) pairing the first and second signals in which an amplitude of each cardiac rhythm cycle of the first signal is aligned to an amplitude of a respective cardiac rhythm cycle of the second signal to form a plurality of paired windows; (iv) for each paired window, calculating values of a ratio R from the paired first and second signals; (v) based on the calculated R values, binning the calculated R values into predetermined frequency bins; and (vi) selecting at least one of the frequency bins to derive a revised ratio, Rrev; and (vii) determining SpO2 from the revised ratio Rrev;
whereinthe method further comprises (viii) obtaining ACamb and DCamb; (viiii) calculating a ratio, Ramb-signal, based on ACamb and ACsignal; (x) providing a zoning schema divided into a plurality of reference zones with each reference zone defined by respective values of first, second and third reference variables which are associated respectively with Rrev, Ramb-signal and DCamb;
each reference zone being associated with a corresponding method of computing SpO2;(xi) comparing Rrev, Ramb-signal and DCamb with respective reference variables of the zoning schema to determine which one of the plurality of reference zones is a selected zone; and (xii) applying the method of computing SpO2 corresponding to the selected zone for determining SpO2; where ACamb is an AC component value of an ambient signal with the first and second light illuminations switched off; DCamb is a DC component value of the ambient signal; and ACsignal is an AC component value of the first or second signal. - View Dependent Claims (5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
if the two maximum bins are directly adjacent to each other, checking if frequency of the two maximum bins exceeds a threshold, and if the threshold is exceeded, selecting the two maximum bins for deriving Rrev.
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10. A method according to claim 9, wherein if the two maximum bins are not directly adjacent to each other, the method further includes
checking if there is an additional bin between the two maximum bins; - and
if there is, selecting the additional bin and the two maximum bins for deriving Rrev.
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11. A method according to claim 10, wherein if there are more than one additional bins between the two maximum bins, the method further includes rejecting the first and second signal waveforms.
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12. A method according to claim 6, wherein there are three maximum bins, and the method further includes
checking if the three maximum bins are directly adjacent to each other; - and
if the three maximum bins are directly adjacent to each other, selecting the three maximum bins for deriving Rrev.
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13. A method according to claim 12, wherein if the three maximum bins are not directly adjacent to each other, the method further includes
checking if there are two maximum bins which are directly adjacent to each other; - and
if there are, checking if frequency of the two directly adjacent maximum bins exceeds a threshold, and if the threshold is exceeded, selecting the two directly adjacent maximum bins for deriving Rrev.
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14. A method according to claim 13, wherein if there are no two maximum bins which are directly adjacent to each other, the method includes rejecting the first and second signal waveforms.
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15. A method according to claim 7, wherein if the threshold is not exceeded, the method includes
selecting at least one peripheral bin directly adjacent to the maximum bin or bins; - and
calculating if the frequency of the at least one peripheral bin and the maximum bin or bins exceeds a further threshold to determine if only the maximum bin or bins are selected or the at least one peripheral bin is selected together with the maximum bin or bins for deriving Rrev.
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16. A method according to claim 1, wherein R is calculated based on
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17. A method according to claim 1, wherein SpO2 is derived from the revised ratio Rrev based on:
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2. -4. (canceled)
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18. (canceled)
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19. A method of determining SpO2 of a subject from an optical measurement, the method comprising:
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(i) in a first interval, obtaining a first signal from a first light illumination and a second signal from second light illumination, the second light illumination having a wavelength which is different from that of the first light illumination; (ii) calculating values of a ratio R from the first and second signals; (iii) in a second interval, obtaining an ambient signal with the first and second light illuminations switched off; (iv) obtaining ACamb and DCamb; (v) calculating a ratio, Ramb-signal, based on ACamb and ACsignal; where ACamb is an AC component value of the ambient signal; DCamb is a DC component value of the ambient signal; ACsignal is an AC component value of the first or second signal; wherein, the method further comprises (vi) providing a zoning schema divided into a plurality of reference zones with each reference zone defined by respective values of first, second and third reference variables which are associated respectively with R, Ramb-signal and DCamb;
each reference zone being associated with a corresponding method of computing SpO2;(vii) comparing R, Ramb-signal and DCamb with respective reference variables of the zoning schema to determine which one of the plurality of reference zones is a selected zone; and (viii) applying the method of computing SpO2 corresponding to the selected zone for determining SpO2. - View Dependent Claims (20, 21, 22)
based on the calculated R values, binning the calculated R values into predetermined frequency bins; and selecting at least one of the frequency bins to derive the revised ratio, Rrev.
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23. (canceled)
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24. A method of determining SpO2 of a subject from an optical measurement, the method comprising:
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(i) in a first interval, obtaining a first signal from a first light illumination and obtaining a second signal from a second light illumination, the second light illumination having a wavelength which is different from that of the first light illumination; (ii) pairing the first and second signals in which an amplitude of each cardiac rhythm cycle of the first signal is aligned to an amplitude of a respective cardiac rhythm cycle of the second signal to form a plurality of paired windows; (iii) for each paired window, calculating values of a ratio R from the paired first and second signals; (iv) based on the calculated R values, binning the calculated R values into predetermined frequency bins; and (v) selecting at least one of the frequency bins to derive a revised ratio, Rrev; (vi) in a second interval, obtaining an ambient signal with the first and second light illuminations switched off; (vii) obtaining ACamb and DCamb; (viii) calculating a ratio, Ramb-signal, based on ACamb and ACsignal; where ACamb is an AC component value of the ambient signal; DCamb is a DC component value of the ambient signal; ACsignal is an AC component value of the first or second signal; wherein, the method further comprises (viiii) providing a zoning schema divided into a plurality of reference zones with each reference zone defined by respective values of first, second and third reference variables which are associated respectively with Rrev, Ramb-signal and DCamb;
each reference zone being associated with a corresponding method of computing SpO2;(x) comparing Rrev, Ramb-signal and DCamb with respective reference variables of the zoning schema to determine which one of the plurality of reference zones is a selected zone; and (xi) applying the method of computing SpO2 corresponding to the selected zone for determining SpO2.
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25. (canceled)
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26. Optical measurement apparatus for determining SpO2 of a subject, the apparatus comprising:
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(a) a photodetector configured to (i) in a first interval, obtain a first signal from a first light illumination and a second signal from second light illumination, the second light illumination having a wavelength which is different from that of the first light illumination; (ii) in a second interval, obtain an ambient signal with the first and second light illuminations switched off; (b) a processor configured to; (iii) calculate values of a ratio R from the first and second signals; (iv) obtain ACamb and DCamb; (v) calculate a ratio, Ramb-signal, based on ACamb and ACsignal; where ACamb is an AC component value of the ambient signal; DCamb is a DC component value of the ambient signal; ACsignal is an AC component value of the first or second signal; and (c) a zoning schema divided into a plurality of reference zones with each reference zone defined by respective values of first, second and third reference variables which are associated respectively with R, Ramb-signal and DCamb;
each reference zone being associated with a corresponding method of computing SpO2;wherein the processor is further configured to; (vi) compare R, Ramb-signal and DCamb with respective reference variables of the zoning schema to determine which one of the plurality of reference zones is a selected zone; and (vii) apply the method of computing SpO2 corresponding to the selected zone for determining SpO2.
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Specification