Wearable Pulse Wave Velocity Blood Pressure Sensor and Methods of Calibration Thereof

• US 20080039731A1
• Filed: 08/17/2007
• Published: 02/14/2008
• Est. Priority Date: 08/22/2005
• Status: Active Grant

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: McCombie, Devin, Asada, Haruhiko, Reisner, Andrew, Shaltis, Phillip
• Granted Patent: US 7,674,231 B2
• Time in Patent Office: Days
• US Class Current: 600/485
• CPC Class Codes: A61B 5/02125 of pulse wave propagation time
• CPC Class Codes: A61B 5/02255 the pressure being controlled by plethysmographic signals, e.g. derived from optical sensors
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives

Abstract

An apparatus and methods for performing a circulatory measurement on an extremity, such as a hand, of a subject. The circulatory measurement results in the derivation of an output circulatory metric that may encompass blood pressure or various other circulatory metrics. An indicator of an input circulatory metric at a locus on the extremity is measured, such as a pulse transit time. To determine the pulse transit time, a first plethysmographic signal may be obtained at a first position on the extremity, while a second plethysmographic signal may be obtained at a second position on the extremity of the subject. A transit time characterizing a circulatory pressure wave is calculated based on the first and second plethysmographic signals, leading to derivation of a wave speed. A calibration is then applied to provide the circulatory measurement based at least on the derived wave speed and a measured indicator of a hydrostatic component of blood pressure. Calibration is provided, in certain described embodiments, by derivation of two calibration parameters, a gain and a pulse transit time at zero pressure. Methods for deriving the calibration parameters include performing measurements under distinct hydrostatic pressure conditions, and based upon a measured derivative with respect to pressure of the pulse wave velocity.

Claims

15-1. The method of claim 15, further comprising measurement of a value related to the derivative of pulse velocity with respect to arterial pressure.

17. An apparatus for performing a circulatory measurement on an extremity of a subject, the apparatus comprising:

a first plethysmographic sensor disposed at a first position on the extremity of the subject;

a second plethysmographic sensor disposed at a second position on the extremity of the subject, wherein the second position is characterized by a distance with respect to the first position;

a processor for obtaining the circulatory measurement based on a derived transit time and the distance between the first and second positions and a calibration and a calibration relating the circulatory measurement to the derived wave speed.

18. The apparatus of claim 17, wherein the first position is at a wrist of the subject.

19. The apparatus of claim 17, wherein the first plethysmographic sensor is adapted to measure blood volume in an ulnar artery of the subject.

20. The apparatus of claim 17, wherein the first plethysmographic sensor is adapted to measure blood volume in a radial artery of the subject.

21. The apparatus of claim 17, wherein the second plethysmographic sensor is adapted to measure blood volume in a digit of the subject.