Blood pressure from inward-facing head-mounted cameras
A system for detecting blood pressure based on imaging photoplethysmography (iPPG) includes a first inward-facing head-mounted camera to capture images of a first region of interest located on the face below the eyes and above the lips (IM ROI1 ) of a user, and a second inward-facing head-mounted camera to capture images of a second region of interest comprising a portion of a temple and/or forehead (IM ROI2 ) of the user. The system further includes a computer to calculate a blood pressure value for the user based on first and second photoplethysmographic signals recognizable in IM ROI1 and IM ROI2 .
1. A system configured to calculate blood pressure, comprising:
a first inward-facing head-mounted camera (HCAM 1 ) configured to capture images of a first region of interest (ROI 1 ) located on the face below the eyes and above the lips (IM ROI1 ) of a user;
a second inward-facing head-mounted camera (HCAM 2 ) configured to capture images of a second region of interest (ROI 2 ) comprising a portion of a temple and/or forehead (IM ROI2 ) of the user; and
a computer configured to calculate a blood pressure value for the user based on first and second imaging photoplethysmographic signals (iPPG 1 , iPPG 2 ) recognizable in IM ROI1 and IM ROI2 , respectively.
2. The system of claim 1 , wherein iPPG 1 and iPPG 2 are indicative of pulse arrival times at ROI 1 and ROI 2 , respectively; and wherein the computer is further configured to extract iPPG 1 and iPPG 2 from IM ROI1 and IM ROI2 , respectively, and to calculate the blood pressure value based on a magnitude of a difference in the pulse arrival times at ROI 1 and ROI 2 .
3. The system of claim 2 , wherein the computer is further configured to utilize calibration measurements of the user's blood pressure, taken by a different device, to calculate parameters that are utilized by the computer to calculate the blood pressure value based on iPPG 1 and iPPG 2 ; whereby the calibration measurements are indicative of the differences between the pulse arrival times at ROI 1 and ROI 2 that correspond to different blood pressure values of the user.
4. The system of claim 1 , wherein the blood pressure value is indicative of one or more of the following values: the systolic blood pressure of the user, the diastolic blood pressure of the user, and the mean arterial pressure of the user.
5. The system of claim 1 , wherein ROI 2 comprises a portion of the right temple and/or the right side of the forehead, and further comprising a third inward-facing head-mounted camera (HCAM 3 ) configured to capture images of a third region of interest (ROI 3 ) comprising a portion of the left temple and/or the left side forehead (IM ROI3 ) of the user; and wherein the computer is further configured to extract from IM ROI3 a third imaging photoplethysmographic signal (iPPG 3 ) and to calculate the blood pressure value of the user also based on iPPG 3 (in addition to iPPG 1 and iPPG 2 ).
6. The system of claim 1 , wherein HCAM 1 is a video camera, and HCAM 1 does not occlude the first region of interest.
7. The system of claim 1 , wherein HCAM 1 is an angle-sensitive pixel sensor camera, weighing less than 1 g.
8. The system of claim 1 , wherein the center of ROI 1 is located more than 6 cm away from the center of ROI 2 ; whereby changes in IM ROI1 that are due to a cardiac pulse wave occur at least 10 ms before, or at least 10 ms after, changes in IM ROI2 occur, which are due to the same cardiac pulse wave.
9. The system of claim 1 , wherein the computer is further configured to generate feature values based on data comprising IM ROI1 and IM ROI2 , and to utilize a model to calculate the blood pressure value based on the feature values; wherein the model was generated based on training data comprising: previously taken IM ROI1 and IM ROI2 , and blood pressure values measured at times corresponding to the previously taken IM ROI1 and IM ROI2 .
10. The system of claim 9 , wherein iPPG 1 and iPPG 2 are indicative of pulse arrival times at ROI 1 and ROI 2 , respectively; wherein the computer is further configured to extract iPPG 1 and iPPG 2 from IM ROI1 and IM ROI2 , respectively; and wherein the feature values comprise a value that is indicative of a difference between when a pulse wave manifested in IM ROI1 and IM ROI2 .
11. The system of claim 9 , wherein iPPG 1 and iPPG 2 are indicative of pulse arrival times at ROI 1 and ROI 2 , respectively; wherein the computer is further configured to extract iPPG 1 and iPPG 2 from IM ROI1 and IM ROI2 , respectively; and wherein the feature values comprise one or more values that are indicative of: (i) a certain blood pressure value of the user that was measured during a certain previous period, and (ii) a difference between when pulse waves of the user manifested in IM ROI1 and IM ROI2 taken during the certain previous period.
12. The system of claim 9 , wherein the previously taken IM ROI1 and IM ROI2 comprise images of body parts of the user, and the blood pressure values corresponding to the previously taken IM ROI1 and IM ROI2 are blood pressure values of the user measured using a device that does not utilize HCAM 1 and HCAM 2 .
13. The system of claim 9 , wherein the computer is further configured to: receive a value indicative of a stress level of the user, and generate at least one of the feature values based on the received value.
14. The system of claim 13 , further comprising an inward-facing head-mounted thermal camera configured to take thermal measurements of at least one of the following regions on the user's face: a periorbital region, a region on the forehead, and a region on the nose; whereby the thermal measurements are indicative of the stress level of the user.
15. The system of claim 9 , wherein the computer is further configured to: receive a value indicative of a hydration level of the user, and generate at least one of the feature values based on the received value.
16. The system of claim 15 , further comprising an additional camera configured to detect intensity of radiation that is reflected from a region of exposed skin of the user; wherein the radiation is in spectral wavelengths chosen to be preferentially absorbed by tissue water, and are chosen from three primary bands of wavelengths of approximately 1100-1350 nm, approximately 1500-1800 nm, and approximately 2000-2300 nm.
17. The system of claim 9 , wherein the computer is further configured to: receive a value indicative of a temperature of the user's body, and generate at least one of the feature values based on the received value.
18. The system of claim 9 , wherein the computer is further configured to: receive a value indicative of the movement of the user's body, and generate at least one of the feature values based on the received value.
19. The system of claim 9 , wherein the computer is further configured to: receive a value indicative of an orientation of the user's head, and generate at least one of the feature values based on the received value.
20. The system of claim 9 , wherein the computer is further configured to: receive a value indicative of consumption of a substance by the user, and generate at least one of the feature values based on the received value; and wherein the substance comprises one or more of the following: a vasodilator, a vasoconstrictor.