Electrical coupling of pulse transit time (PTT) measurement system to heart for blood pressure measurement

Patent metadata

Field	Value
Publication number	US-11918324-B2
Application number	US-202016990650-A
Country	US
Kind code	B2
Filing date	Aug 11, 2020
Priority date	Sep 8, 2014
Publication date	Mar 5, 2024
Grant date	Mar 5, 2024

Abstract

A pulse transit time is measured non-invasively and used to calculate a blood pressure value. A method of determining one or more blood pressure values includes propagating an alternating drive current through a thorax of a subject via electrodes located on a wrist-worn device. Resulting voltage levels of the subject are sensed by the wrist-worn device. The voltage levels are processed to detect when a volume of blood is ejected from the left ventricle. Output from a pulse arrival sensor coupled to the wrist-worn device is processed to detect when a blood pressure pulse generated by ejection of the volume of blood from the left ventricle arrives at the wrist. A pulse transit time (PTT) for transit of the blood pressure pulse from the left ventricle to the wrist is calculated. One or more blood pressure values for the subject are determined based on the PTT.

First claim

What is claimed is:

1. A method of determining one or more blood pressure values of a subject, the method comprising:
propagating an alternating drive current through the subject between a first drive current electrode and a second drive current electrode, wherein the second drive current electrode is externally located on a wrist-worn device worn on a wrist of the subject and engaged with the subject so that a portion of the alternating drive current travels through a thorax of the subject, and wherein the first drive current electrode is non-invasively engaged with the subject's skin at the wrist;
sensing voltage levels of the subject resulting from the alternating drive current via a first sense electrode and a second sense electrode, wherein the second sense electrode is externally located on the wrist-worn device and engaged with the subject so as to sense a voltage level induced by the alternating drive current, and wherein the first sense electrode is non-invasively engaged with the subject's skin at the wrist;
processing the voltage levels to detect when a volume of blood is ejected from the left ventricle;
processing output from a pulse arrival sensor coupled to the wrist-worn device to detect when a blood pressure pulse generated by ejection of the volume of blood from the left ventricle arrives at the wrist;
calculating a pulse transit time (PTT) for transit of the blood pressure pulse from the left ventricle to the wrist; and
determining one or more blood pressure values for the subject based on the PTT.

2. The method of claim 1 , wherein:
the second drive current electrode is in contact with a first finger of an arm of the subject opposite to an arm of the subject on which the wrist-worn device is worn when the alternating drive current is propagated and the voltage levels are sensed; and
the second sense electrode is in contact with a second finger of the arm of the subject opposite to the arm of the subject on which the wrist-worn device is worn when the alternating drive current is propagated and the voltage levels are sensed.

3. The method of claim 2 , wherein each of the first drive current electrode and the first sense electrode are located on the wrist-worn device so that contact pressure between the first finger and the second drive current electrode and contact pressure between the second finger and the second sense electrode increases contact pressure between the wrist and each of the first drive current electrode and the first sense electrode.

4. The method of claim 3 , wherein:
the wrist-worn device comprises an elongate wrist band; and
the first drive current electrode, the second drive current electrode, the first sense electrode, and the second sense electrode are disposed on the elongate wrist band.

5. The method of claim 1 , wherein each of the first drive current electrode, the second drive current electrode, the first sense electrode, and the second sense electrode is a dry electrode.

6. The method of claim 1 , wherein the alternating drive current is propagated and the voltage levels are sensed when each of the second drive current electrode and the second sense electrode is contacted with skin on the subject's thorax.

7. The method of claim 1 , wherein the pulse arrival sensor comprises a PPG sensor.

8. The method of claim 7 , 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 are further based on the tone of the subject's blood vessels.

9. The method of claim 7 , further comprising detecting different mean penetration depths of light emitted by the PPG sensor by using at least two light detectors disposed at different distances from a light source of the PPG sensor to detect when the blood pressure pulse arrives at the wrist at a deeper of the different mean penetration depths.

10. The method of claim 9 , further comprising processing one or more signals from the PPG sensor to detect when the blood pressure pulse arrives at the deep blood plexus (DBP) layer at the wrist.

11. The method of claim 7 , further comprising detecting different mean penetration depths of light emitted by the PPG sensor by emitting different wavelengths of light from different light sources.

12. The method of claim 11 , wherein the different light sources comprises at least two of an infra-red light source, a red light source, or a green light source.

13. The method of claim 11 , wherein the different wavelengths of light comprise 525 nm and 940 nm.

14. The method of claim 9 , comprising processing one or more signals from the PPG sensor to detect when the blood pressure pulse arrives at the wrist within the subject's radial artery.

15. The method of claim 1 , wherein:
the pulse arrival sensor comprises a pulse pressure sensor; and
the pulse pressure sensor comprises at least one of a pressure transducer, an accelerometer, or a strain gauge.

16. The method of claim 1 , further comprising calibrating the one or more blood pressure values based on calibration data comprising a reference blood pressure value for the subject and a reference PTT for transit of a reference blood pressure pulse from the left ventricle to the wrist.

17. The method of claim 1 , further comprising calculating trending data for a time period based on the one or more blood pressure values.

18. The method of claim 17 , wherein the time period comprises one or more days, one or more weeks, one or more months, or one or more years.

19. The method of claim 1 , further comprising transmitting the one or more blood pressure values to a mobile device, table, tablet, computer, or database.

20. The method of claim 1 , further compromising generating an electrocardiogram (EKG) for the subject from one or more signals generated by a set of the first drive current electrode, the second drive current electrode, the first sense electrode, and the second sense electrode.

Assignees

• Apple Inc

Inventors

• Sullivan Thomas J
• Dougherty Wren Nancy
• Kimoto Richard C
• Klaassen Erno
• Narasimhan Ravi K
• Waydo Stephen J
• Whitehurst Todd K
• Young Derek Park-Shing
• Quijano Santiago
• Zeng Zijing

Classifications

• A61B5/02125 Primary

  of pulse wave propagation time · CPC title

• A61B5/14551

  for measuring blood gases · CPC title

• A61B5/282 Primary

  Holders for multiple electrodes (for introduction into the body A61B5/287) · CPC title

• A61B5/681

  Wristwatch-type devices · CPC title

• A61B5/6824

  Arm or wrist · CPC title