# US 10,945,617 B2 · Low-complexity sensor displacement tolerant pulse oximetry based heart rate measurement > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,945,617 B2 - Document ID: US10945617B2 - Status: Granted - Kind: B2 - Application number: 15/634,521 - Filed: 2017-06-27 - Published: 2017-10-19 - Granted: 2021-03-16 - Earliest claimed: 2013-01-28 - Assignees: Texas Instruments Incorporated - Applicants: Texas Instruments Incorporated - Inventors: Vitali Loseu; Sourabh Ravindran - Web page: https://patentgrep.com/patent/US10945617B2 ## CPC - A61B 5/02416: {using photoplethysmograph signals, e.g. generated by infrared radiation (A61B5/14552 takes precedence)} - A61B 5/681: {Wristwatch-type devices} - A61B 5/7207: {of noise induced by motion artifacts} - A61B 5/725: {using specific filters therefor, e.g. Kalman or adaptive filters (specific diagnostics methods using using bioelectric or biomagnetic signals A61B5/316)} - A61B: DIAGNOSIS; SURGERY; IDENTIFICATION (usefulness limited to only animals A61D) ## Abstract Methods for heart rate measurement based on pulse oximetry are provided that can tolerate some degree of relative displacement of a photoplethysmograph (PPG) heart rate monitor device. In some methods, artifact compensation based on a reference signal is performed on the PPG signal data to remove artifacts in the signal that may be caused, for example, by changes in ambient light and/or motion of a person wearing the monitor device. The reference signal used for artifact compensation may be generated using an LED of a complementary wavelength to that of the LED used to generate the PPG signal, or by driving an LED at a lower current than the current applied to generate the PPG signal. ## Claims ### Claim 1 A method performed by a photoplethysmograph (PPG) heart rate monitor device, the method comprising: receiving an accelerometer signal from a motion sensor of the heart rate monitor device; capturing a PPG light signal, in which the PPG light signal is: filtered when the accelerometer signal is below a threshold; or motion compensated when the accelerometer signal is above the threshold; detecting a pulse in a portion of the filtered or motion compensated PPG light signal, including detecting a start point of the pulse; determining a summit point and an end point of the pulse based on the start point of the pulse, in which determining the summit point includes: determining a first maximum point within a first portion of the pulse; determining a second maximum point after the first maximum point; determining a direct linear path difference between the first maximum point and the second maximum point; determining an indirect path difference between the first maximum point and the second maximum point; and selecting the summit point as either the first maximum point or the second maximum point based on a comparison of the direct linear path difference and the indirect path difference; estimating a pulse rate based on the start point, the summit point, and the end point; and outputting the estimated pulse rate to another device. ### Claim 2 (depends on 1) The method of claim 1, wherein the selecting the summit point includes: selecting the first local maximum point as the summit point when the direct linear path difference does not exceed the indirect path difference by a predetermined factor; and selecting the second local maximum point as the summit point; when the direct linear path difference exceeds the indirect path difference by the predetermined factor. ### Claim 3 A method performed by a photoplethysmograph (PPG) heart rate monitor device, the method comprising: receiving an accelerometer signal from a motion sensor of the heart rate monitor device; capturing a PPG light signal, in which the PPG light signal is: filtered, when the accelerometer signal is below a threshold; or motion compensated, when the accelerometer signal is above the threshold; detecting a pulse in a portion of the filtered or motion compensated PPG light signal, including detecting a start point of the pulse; determining a summit point and an end point of the pulse based on the start point of the pulse, wherein determining the end point includes: determining a first local minimum point after the summit point of the pulse; determining a second minimum point after the first minimum point; determining a first path between the summit point and the first minimum point; determining a second path between the summit point and the second minimum point; and selecting the end point as either the first minimum point or the second minimum point based on a comparison of the first path and the second path; estimating a pulse rate based on the start point, the summit point, and the end point; and outputting the estimated pulse rate to another device. ### Claim 4 (depends on 3) The method of claim 3, wherein the selecting the end point includes: determining a first normalized difference between a first length and a second length of the first minimum point, wherein: the first length is measured between the start point and the summit point; and the second length is measured between the summit point and the first minimum point; determining a second normalized difference between a first length and a second length of the second minimum point, wherein: the first length is measured between the start point and the summit point; and the second length is measured between the summit point and the second minimum point; and comparing the first normalized difference with the second normalized difference. ### Claim 5 (depends on 4) The method of claim 4, wherein the selecting the end point includes: selecting the first minimum point as the end point when the second normalized difference is greater than a predetermined multiple of the first normalized difference; and selecting the second minimum point as the end point when the second normalized difference is less than the predetermined multiple of the first normalized difference.