Blood pressure from inward-facing head-mounted cameras

• US 10,376,163 B1
• Filed: 04/04/2019
• Issued: 08/13/2019
• Est. Priority Date: 06/14/2015
• Status: Active Grant

• Current Assignee: Facense Ltd.
• Original Assignee: Facense Ltd.
• Inventors: Tzvieli, Arie, Frank, Ari M, Tzvieli, Ori, Thieberger, Gil
• Primary Examiner(s): Porta, David P
• Assistant Examiner(s): Boosalis, Fani
• Application Number:
  US16/375,841
• Publication Number:
  US 20190223737A1
• Time in Patent Office: 131 Days
• CPC Class Codes: A61B 2576/00 Medical imaging apparatus involving image processing or analysis A61B1/00009, A61B6/52 and A61B8/52 take precedence; image processing per se G06T; details of algorithms for analysing medical images G06T7/0012
• CPC Class Codes: A61B 5/0002 Remote monitoring of patients using telemetry, e.g. transmission of vital signals via a communication network A61B5/07 takes precedence; transmission systems for measured values G08C; transmission H04B; transmission of digital information H04L; wireless communication networks H04W
• CPC Class Codes: A61B 5/0064 Body surface scanning
• CPC Class Codes: A61B 5/0077 Devices for viewing the surface of the body, e.g. camera, magnifying lens
• CPC Class Codes: A61B 5/01 Measuring temperature of body parts ; Diagnostic temperature sensing, e.g. for malignant or inflamed tissue clinical contact thermometers G01K13/20
• CPC Class Codes: A61B 5/02125 of pulse wave propagation time
• CPC Class Codes: A61B 5/02416 using photoplethysmograph signals, e.g. generated by infrared radiation A61B5/14552 takes precedence
• CPC Class Codes: A61B 5/0261 using optical means, e.g. infrared light
• CPC Class Codes: A61B 5/0295 using plethysmography, i.e. measuring the variations in the volume of a body part as modified by the circulation of blood therethrough, e.g. impedance plethysmography
• CPC Class Codes: A61B 5/11 Measuring movement of the entire body or parts thereof, e.g. head or hand tremor, mobility of a limb for measuring pulse A61B5/02 ;A61B5/1038 takes precedence; motion detection to correct for motion artifacts in physiological signals A61B5/721
• CPC Class Codes: A61B 5/165 Evaluating the state of mind, e.g. depression, anxiety
• CPC Class Codes: A61B 5/6821 Eye
• CPC Class Codes: A61B 5/6826 Finger
• CPC Class Codes: A61B 5/6831 Straps, bands or harnesses
• CPC Class Codes: G02B 2027/0178 Eyeglass type eyeglass details G02C
• CPC Class Codes: G02B 27/017 Head mounted
• CPC Class Codes: G16H 30/40 for processing medical images, e.g. editing

Abstract

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.

Claims

1. A system configured to calculate blood pressure, comprising:

a first inward-facing head-mounted camera (HCAM₁) configured to capture images of a first region of interest (ROI₁) located on the face below the eyes and above the lips (IM_ROI1) of a user;

a second inward-facing head-mounted camera (HCAM₂) configured to capture images of a second region of interest (ROI₂) 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 (iPPG₁, iPPG₂) recognizable in IM_ROI1 and IM_ROI2, respectively.

2. The system of claim 1, wherein iPPG₁ and iPPG₂ are indicative of pulse arrival times at ROI₁ and ROI₂, respectively;

and wherein the computer is further configured to extract iPPG₁ and iPPG₂ 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 ROI₁ and ROI₂.

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 iPPG₁ and iPPG₂;

whereby the calibration measurements are indicative of the differences between the pulse arrival times at ROI₁ and ROI₂ 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 ROI₂ 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 (HCAM₃) configured to capture images of a third region of interest (ROI₃) 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 (iPPG₃) and to calculate the blood pressure value of the user also based on iPPG₃ (in addition to iPPG₁ and iPPG₂).

6. The system of claim 1, wherein HCAM₁ is a video camera, and HCAM₁ does not occlude the first region of interest.

7. The system of claim 1, wherein HCAM₁ is an angle-sensitive pixel sensor camera, weighing less than 1 g.

8. The system of claim 1, wherein the center of ROI₁ is located more than 6 cm away from the center of ROI₂;

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 iPPG₁ and iPPG₂ are indicative of pulse arrival times at ROI₁ and ROI₂, respectively;

wherein the computer is further configured to extract iPPG₁ and iPPG₂ 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 iPPG₁ and iPPG₂ are indicative of pulse arrival times at ROI₁ and ROI₂, respectively;

wherein the computer is further configured to extract iPPG₁ and iPPG₂ 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 HCAM₁ and HCAM₂.

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.