# US 2017/0281024 A1 · Wrist worn accelerometer for pulse transit time (ptt) measurements of blood pressure > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2017/0281024 A1 - Document ID: US20170281024A1 - Status: Published application - Kind: A1 - Application number: 15/507,607 - Filed: 2015-09-08 - Published: 2017-10-05 - Earliest claimed: 2014-09-08 - Assignees: Apple Inc. - Applicants: Apple, Inc. - Inventors: Ravi Narasimhan; Richard C. Kimoto; Thomas J. Sullivan; Todd K. Whitehurst; Derek Park-shing Young; Zijing Zeng; Erno Klaassen - Web page: https://patentgrep.com/patent/US20170281024A1 ## CPC - A61B 5/02125: {of pulse wave propagation time} - A61B 5/11: Measuring movement of the entire body or parts thereof, e.g. head or hand tremor or mobility of a limb {(A61B5/1038 takes precedence; motion detection to correct for motion artifacts in physiological signals A61B5/721)} - A61B 5/681: {Wristwatch-type devices} - A61B 5/6824: {Arm or wrist} - A61B 5/024: Measuring pulse rate or heart rate - A61B 5/02416: {using photoplethysmograph signals, e.g. generated by infrared radiation (A61B5/14552 takes precedence)} - A61B 5/1102: {Ballistocardiography} - A61B: DIAGNOSIS; SURGERY; IDENTIFICATION (usefulness limited to only animals A61D) ## Abstract Wrist-worn devices and related methods measure a pulse transit time non-invasively and calculate a blood pressure value using the pulse transit time. A wrist-worn device includes an accelerometer, a photo-plethysmogram (PPG) or a pulse pressure sensor, and a controller. The PPG or the pulse pressure sensor coupled to the wrist-worn device for detecting an arrival of a blood pressure pulse at the user's wrist. The controller is configured to process output signals from the accelerometer to detect when the blood pressure pulse is propagated from the left ventricle of the user's heart, process a signal from the PPG or the pulse pressure sensor to detect when the blood pressure pulse arrives at the wrist, calculate a pulse transit time (PTT) for propagation of the blood pressure pulse from the left ventricle to the wrist, and generate one or more blood pressure values for the user based on the PTT. ## Claims ### Claim at position 1 -27. (canceled) ### Claim 28 A method for determining a pressure of blood within a cardiovascular system of a user, the cardiovascular system including a heart and the user having a wrist covered by skin, the method comprising: detecting, with an accelerometer of a wrist-worn device non-invasively engaging an anterior surface of the wrist of the user, a first signal indicative of when blood is ejected from the left ventricle of the subject's heart; detecting, with a PPG or a pulse pressure sensor of the wrist-worn device non-invasively engaging the skin on the wrist of the user, a second signal indicative when a blood pressure pulse corresponding to the blood ejection arrives at the wrist; calculating a pulse transit time (PTT) for the blood pressure pulse from the ejection of the blood from the left ventricle to arrival of the blood pressure pulse at the wrist; and generating one or more relative blood pressure values for the subject based on the PTT. ### Claim 29 (depends on 28) The method of claim 28, comprising detecting when the accelerometer is positioned on the user's chest. ### Claim 30 (depends on 28) The method of claim 28, comprising: storing acceleration data corresponding to the accelerometer output for a recording time period; and using the detected arrival time of the blood pressure pulse at the wrist to select a candidate time period within the recording time period to select the acceleration data to evaluate to identify when the blood ejection from the user's left ventricle occurred corresponding to the blood pressure pulse. ### Claim 31 (depends on 30) The method of claim 30, comprising: based on evaluation of the accelerometer output, identifying two or more candidate times for when the blood ejection from the left ventricle occurred within the candidate time period; and selecting one of the candidate times closest to a target time within the candidate time period for the PTT calculation. ### Claim 32 (depends on 30) The method of claim 30, wherein the candidate time period is from about 100 ms to about 300 ms before a detected time when the pulse arrives at the user's wrist. ### Claim 33 (depends on 28) The method of claim 28, comprising processing the accelerometer output with a bandpass filter to remove noise. ### Claim 34 (depends on 33) The method of claim 33, wherein the bandpass filter attenuates frequencies less than about 0.3 Hz and greater than about 10 Hz. ### Claim 35 (depends on 28) The method of claim 28, comprising processing the PPG or pressure sensor output with a bandpass filter to remove noise. ### Claim 36 (depends on 35) The method of claim 35, wherein the bandpass filter attenuates frequencies less than about 0.3 Hz and greater than about 10 Hz. ### Claim 37 (depends on 28) The method of claim 28, comprising: differentiating the PPG or pressure sensor signal with respect to time; and evaluating the differentiated signal to select a time of arrival of the pressure pulse at the wrist prior to arrival of a reflection of the blood pressure pulse at the wrist. ### Claim 38 (depends on 28) The method of claim 28, wherein the accelerometer output comprises accelerations measured in three directions, and the method further comprises: calculating combined acceleration magnitude values from the measured accelerations, the combined acceleration magnitudes values being based on a combination of the measured acceleration in at least two directions; and processing the combined acceleration magnitude values to detect when blood is ejected from the left ventricle of the user's heart. ### Claim 39 (depends on 38) The method of claim 38, comprising performing an eigenvector-based principle component analysis of the measured accelerations to calculate the combined acceleration magnitude values so as to reflect increased sensitivity to blood ejections from the left ventricle. ### Claim 40 (depends on 28) The method of claim 28, further comprising processing output from the PPG sensor to determine a tone of the subject's blood vessels, and wherein the one or more blood pressure values generated for the subject is further based on the determined tone of the subject's blood vessels. ### Claim 41 (depends on 28) The method of claim 28, wherein the generation of the one or more blood pressure values is further based on calibration data including measured blood pressure values and corresponding PTTs for the subject. ### Claim 42 (depends on 28) The method of claim 28, further comprising calculating trending data for a time period based on the one or more relative blood pressure values. ### Claim 43 (depends on 42) The method of claim 42, wherein the time period comprises one or more days, one or more weeks, one or more months, or one or more years. ### Claim 44 (depends on 28) The method of claim 28, further comprising transmitting the one or more relative blood pressure measurements to a mobile device, table, computer, or database. ### Claim 45 (depends on 28) The method of claim 28, further comprising detecting different mean penetration depths of light emitted by the PPG sensor by at least one of: a) using at least two light detectors disposed at different distances from a light source of the PPG sensor; and b) using a plurality of light sources configured to emit different wavelengths of light. ### Claim 46 (depends on 45) The method of claim 45, further comprising using at least two different mean penetration depths to evaluate light returned from a deeper penetration depth relative to the two different mean penetration depths. ### Claim 47 (depends on 45) The method of claim 45, comprising processing one or more signals from the PPG sensor to detect when the blood pressure pulse corresponding to the ejected blood arrives at the deep blood plexus (DBP) layer at the subject's wrist. ### Claim 48 (depends on 45) The method of claim 45, comprising processing one or more signals from the PPG sensor to detect when the blood pressure pulse corresponding to the ejected blood arrives at the subject's wrist within the subject's radial artery. ### Claim 49 (depends on 45) The method of claim 45, comprising processing one or more signals from the PPG sensor to determine a tone of the subject's blood vessels, and wherein the one or more blood pressure values generated for the subject is further based on the determined tone of the subject's blood vessels. ### Claim 50 (depends on 28) The method of claim 28, wherein generating the one or more relative blood pressure values for the subject based on the PTT comprises: generating an estimated elevation difference between the wrist-worn device and the user's heart; and using the estimated elevation difference to account for hydrostatic elevation differences in blood pressure within the user. ### Claim 51 (depends on 50) The method of claim 50, wherein the estimated elevation difference between the wrist-worn device and the user's heart is generated based on output from one or more pressure sensors or an estimated arm posture derived from output from the accelerometer.