Method and apparatus for cuff-less blood pressure measurement in a mobile device

• US 10,398,324 B2
• Filed: 08/31/2018
• Issued: 09/03/2019
• Est. Priority Date: 03/03/2016
• Status: Active Grant

• Current Assignee: The Board of Trustees of Michigan State University (Michigan State University), University of Maryland, College Park
• Original Assignee: The Board of Trustees of Michigan State University (Michigan State University)
• Inventors: Mukkamala, Ramakrishna, Chandrasekhar, Anand, Hahn, Jin-Oh
• Primary Examiner(s): Nganga, Boniface N
• Application Number:
  US16/118,530
• Publication Number:
  US 20190008399A1
• Time in Patent Office: 368 Days
• CPC Class Codes: A61B 2560/0462 Apparatus with built-in sensors
• CPC Class Codes: A61B 2562/0238 Optical sensor arrangements for performing transmission measurements on body tissue
• CPC Class Codes: A61B 2562/0247 Pressure sensors
• CPC Class Codes: A61B 5/0077 Devices for viewing the surface of the body, e.g. camera, magnifying lens
• CPC Class Codes: A61B 5/02055 Simultaneously evaluating both cardiovascular condition and temperature
• CPC Class Codes: A61B 5/02141 Details of apparatus construction, e.g. pump units or housings therefor, cuff pressurising systems, arrangements of fluid conduits or circuits A61B5/02233, A61B5/0235 take precedence
• CPC Class Codes: A61B 5/02225 using the oscillometric method
• 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 5/6898 Portable consumer electronic devices, e.g. music players, telephones, tablet computers
• CPC Class Codes: A61B 5/706 Indicia not located on the patient, e.g. floor marking
• CPC Class Codes: A61B 5/743 Displaying an image simultaneously with additional graphical information, e.g. symbols, charts, function plots

Abstract

A system and method is presented for cuff-less blood pressure measurement in a mobile device. A key aspect of this disclosure is the discovery of a new location for blood pressure measurement at the fingertip of a subject and that reflectance-mode photoplethysmography can be used to help make this measurement. Through experiments in human subjects, it was discovered that it is indeed possible to measure systemic blood pressure by having a subject press the fingertip against a reflectance-mode photo-plethysmography-force sensor unit under visual guidance and then compute blood pressure from the resulting variable-amplitude blood volume oscillations and applied pressure via an oscillometric algorithm.

Claims

1. A system for measuring blood pressure, comprising:

a mobile device including a processor and a display unit; and

an encasing configured to encase the mobile device, wherein the encasing includes;

a sensing unit integrated into the encasing and configured to measure blood pressure at a fingertip of a user, wherein the sensing unit includes a reflectance-mode photo-plethysmography (PPG) sensor configured to measure blood volume oscillations and a force sensor configured to measure pressure applied by the fingertip; and

a visual guide disposed on the encasing and arranged in relation to the sensing unit, where the visual guide comprise indicia to guide the user in placing a base of fingernail and a center of the finger in relation to the sensing unit;

wherein the system includes a non-transitory computer-readable medium that stores instructions that, when executed by the processor, cause the processor to;

measure pressure applied to the sensing unit by a fingertip of a user,

measure blood volume oscillations in the fingertip,

guide the user via the display unit to vary pressure being applied to the sensing unit while the blood volume oscillations and pressure are measured,

generate an oscillogram from the measured pressure and the measured blood volume oscillations, where the oscillogram plots amplitude of blood volume oscillations as a function of the measured pressure,

calculate a blood pressure value from the oscillogram, and

present the blood pressure value on the display unit.

2. The system of claim 1 wherein the PPG sensor includes at least one light emitting diode and an array of photodetectors.

3. The system of claim 2 wherein the maximum amplitude photodetector signal is used as the blood volume oscillations.

4. The system of claim 1 wherein the force sensor is an array of force transducer elements.

5. The system of claim 4 wherein an area of force application is determined based on the force outputs of each element.

6. The system of claim 1 wherein the sensing unit further includes a temperature sensor.

7. The system of claim 1 further includes instructions that, when executed by the processor, cause the processor to guide the user to hold the device at a height aligned with the heart of the user.

8. The system of claim 7 further includes instructions that, when executed by the processor, cause the processor to capture an image of the user with a camera, compare the captured image to a reference image of the user, and instruct the user to hold the mobile device at a height aligned with the heart of the user based on the comparison of the captured image with the reference image, where the reference image was captured when the device was being held at a height aligned with the heart of the user.

9. The system of claim 1 further includes instructions that, when executed by the processor, cause the processor to capture an image of the user with a camera, compare the captured image to a reference image of the user, detect the height at which the device is being held relative to the heart based on the comparison of the captured image with the reference image, where the reference image was captured when the device was being held at a height aligned with the heart of the user, and compensate the calculated blood pressure value in accordance with the detected height.

10. The system of claim 1 wherein the processor generates a blood pressure value by

representing the oscillogram with a mathematical model, wherein the mathematical model is defined in terms of parameters with unknown values, the parameters indicating finger systolic pressure and finger diastolic pressure and specifying a nonlinear blood volume-transmural pressure relationship of a fingertip artery;

estimating the parameters of the mathematical model by fitting the mathematical model to the oscillogram; and

computing brachial systolic pressure and diastolic pressure using the parameter estimates.

11. The system of claim 10 wherein computing brachial systolic pressure and diastolic pressure further comprises use of a transfer function.

13. The system of claim 10 further comprises using a transfer function to calculate the blood pressure value at the level of brachial artery.

12. A system for measuring blood pressure, comprising:

a mobile device including a processor and a display unit; and

an encasing configured to encase the mobile device, wherein the encasing includes;

a sensing unit integrated into the encasing and configured to measure blood pressure at a fingertip of a user, wherein the sensing unit includes a reflectance-mode photo-plethysmography (PPG) sensor configured to measure blood volume oscillations and a force sensor configured to measure pressure applied by the fingertip; and

a visual guide disposed on the encasing and arranged in relation to the sensing unit, where the visual guide comprise indicia to guide the user in placing a surface of the fingertip on an opposite side of the finger from a fingernail on the finger and distal from a distal interphalangeal joint of the finger onto the sensing unit;

wherein the system includes a non-transitory computer-readable medium that stores instructions that, when executed by the processor, cause the processor to;

measure pressure applied to the sensing unit by a fingertip of a the user,

measure blood volume oscillations in the fingertip,

guide the user via the display unit to vary pressure being applied to the sensing unit while the blood volume oscillations and pressure are measured,

generate an oscillogram from the measured pressure and the measured blood volume oscillations, where the oscillogram plots amplitude of blood volume oscillations as a function of the measured pressure,

calculate a blood pressure value at level of brachial artery from the oscillogram, and

present the blood pressure value on the display unit.