Methods and devices for reduction of motion-induced noise in optical vascular plethysmography

• US 6,997,879 B1
• Filed: 07/09/2002
• Issued: 02/14/2006
• Est. Priority Date: 07/09/2002
• Status: Expired due to Fees

• Current Assignee: Pacesetter Incorporated (Abbott Laboratories Incorporated)
• Original Assignee: Pacesetter Incorporated (Abbott Laboratories Incorporated)
• Inventors: Turcott, Robert G.
• Primary Examiner(s): Nasser, Robert L.
• Assistant Examiner(s): Natnithithadha, Navin
• Application Number:
  US10/192,368
• Time in Patent Office: 1,316 Days
• Field of Search: 600/507, 600500-504, 600/481, 600/485, 600/476, 600/477, 600/479, 600/480, 600/473, 600/475, 600310-341
• US Class Current: 600/507
• CPC Class Codes: A61B 5/0261 using optical means, e.g. infrared light
• CPC Class Codes: A61B 5/14552 Details of sensors specially adapted therefor
• CPC Class Codes: A61B 5/7214 using signal cancellation, e.g. based on input of two identical physiological sensors spaced apart, or based on two signals derived from the same sensor, for different optical wavelengths
• CPC Class Codes: A61N 1/36514 controlled by a physiological quantity other than heart potential, e.g. blood pressure controlled by two or more physical parameters A61N1/36585

Abstract

Methods and devices are provided for reducing motion artifacts when monitoring volume changes in blood vessels. Light having a first wavelength and light having a second wavelength are transmitted through a human appendage, toward the epidermis of a patient, or through tissue within the body of a patient. A portion of the light having the first wavelength and a portion of the light having the second wavelength is received. A first signal is produced based on the received portion of light having the first wavelength. A second signal is produced based on the received portion of light having the second wavelength. One of the first and second signals is subtracted from the other to produce a plethysmography signal that is representative of volume changes in blood vessels of patient tissue.

Claims

1. A method for reducing motion artifacts when monitoring volume changes in blood vessels, comprising the following steps:

(a) transmitting, from a light source implanted within a patient'"'"'s body, light having a first wavelength and light having a second wavelength toward tissue within the patient'"'"'s body;

(b) receiving a portion of the light having the first wavelength and a portion of the light having the second wavelength reflected from the tissue;

(c) producing a first signal, based on the received portion of light having the first wavelength, and a second signal, based on the received portion of light having the second wavelength;

(d) subtracting one of the first and second signals from the other to produce a plethysmography signal that is representative of volume changes in blood vessels of the tissue; and

(e) setting intensities such that a ratio of an intensity of the light having the first wavelength over an intensity of the light having the second wavelength is approximately equal to a ratio of an effective absorption coefficient of non-blood tissue at the second wavelength over an effective absorption coefficient of non-blood tissue at the first wavelength.

2. The method of claim 1 wherein the setting intensities step comprises setting the intensities of the light transmitted at step (a).

3. A method for reducing motion artifacts when monitoring volume changes in blood vessels, comprising the following steps of:

(a) transmitting light having a first wavelength and light having a second wavelength through a human appendage;

(b) setting the transmitted intensity of at least one of the light having the first wavelength and the light having the second wavelength such that a ratio of an intensity of the light having the first wavelength over an intensity of the light having the second wavelength is approximately equal to a ratio of an effective absorption coefficient of non-blood tissue at the second wavelength over an effective absorption coefficient of non-blood tissue at the first wavelength;

(c) receiving a portion of the light having the first wavelength and a portion of the light having the second wavelength;

(d) producing a first signal, based on the received portion of light having the first wavelength, and a second signal, based on the received portion of light having the second wavelength; and

(e) subtracting one of the first and second signals from the other to produce a plethysmography signal that is representative of volume changes in blood vessels of the human appendage.

4. The method of claim 3, wherein the setting intensities step comprises setting the intensities of the light transmitted at step (a).

5. A method for reducing motion artifacts when monitoring volume changes in blood vessels, comprising the following steps:

(a) applying light having a first wavelength and light having a second wavelength to an epidermis of a patient;

(b) detecting, at the epidermis of the patient, a portion of the light having the first wavelength and a portion of the light having the second wavelength;

(c) producing a first signal, based on the detected portion of light having the first wavelength, and a second signal, based on the received portion of light having the second wavelength;

(d) setting intensities such that a ratio of an intensity of the light having the first wavelength over an intensity of the light having the second wavelength is approximately equal to a ratio of an effective absorption coefficient of non-blood tissue at the second wavelength over an effective absorption coefficient of non-blood tissue at the first wavelength; and

(e) subtracting one of the first and second signals from the other to produce a plethysmography signal that is representative of volume changes in blood vessels beneath the epidermis of the patient.

6. The method of claim 5, wherein the setting intensities step comprises setting the intensities of the light applied at step (a).

7. A method for reducing motion artifacts when monitoring volume changes in blood vessels, comprising the following steps of:

(a) transmitting light having a first wavelength and light having a second wavelength through a human appendage;

(b) receiving a portion of the light having the first wavelength and a portion of the light having the second wavelength;

(c) producing a first signal, based on the received portion of light having the first wavelength, and a second signal, based on the received portion of light having the second wavelength;

(d) adjusting a ratio of a gain of the first signal and a gain of the second signal to reduce motion artifacts; and

(e) subtracting one of the first and second signals from the other to produce a plethysmography signal that is representative of volume changes in blood vessels of the human appendage.

8. The method of claim 7, wherein the ratio is adjusted to minimize the motion artifacts.

9. A method for reducing motion artifacts when monitoring volume changes in blood vessels, comprising the following steps:

(a) applying light having a first wavelength and light having a second wavelength to an epidermis of a patient;

(b) detecting, at the epidermis of the patient, a portion of the tight having the first wavelength and a portion of the light having the second wavelength;

(c) producing a first signal, based on the detected portion of light having the first wavelength, and a second signal, based on the received portion of light having the second wavelength;

(d) adjusting a ratio of a gain of the first signal and a gain of the second signal to reduce motion artifacts; and

(e) subtracting one of the first and second signals from the other to produce a plethysmography signal that is representative of volume changes in blood vessels beneath the epidermis of the patient.

10. The method of claim 9, wherein the ratio is adjusted to minimize the motion artifacts.