Photoplethysmograph signal-to-noise line enhancement

• US 6,699,199 B2
• Filed: 06/11/2002
• Issued: 03/02/2004
• Est. Priority Date: 04/18/2000
• Status: Expired due to Term

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Asada, Haruhiko H., Shaltis, Phillip, Hutchinson, Reginald C.
• Primary Examiner(s): Hindenburg, Max F.
• Assistant Examiner(s): Natnithithadha, Navin
• Application Number:
  US10/167,069
• Publication Number:
  US 20020169381A1
• Time in Patent Office: 630 Days
• Field of Search: 600/504, 600/505, 600/507, 600/473, 600/476, 600/479, 600/480, 600/300, 600/310, 600/561, 600/481, 600/587
• US Class Current: 600/504
• CPC Class Codes: A61B 5/14552 Details of sensors specially adapted therefor
• CPC Class Codes: A61B 5/6826 Finger
• CPC Class Codes: A61B 5/6838 Clamps or clips

Abstract

A ring plethysmograph having a pressure adjustment for locally pressurizing one side of a finger thereby biasing the pressure on an artery wall so that the plethysmograph is optimally sensitive without interfering with blood flow. An auxiliary photodetector, possibly with a second light source, is disposed on the low-pressure side of the finger for two purposes: providing a noise reference for canceling noise on the plethysmograph signal, and also for providing a separate motion signal for monitoring the activity level of a patient.

Claims

1. In a photoplethysmograph for characterizing blood volume of the type having a light source and a detector disposed about a region of body tissue containing a specified blood vessel carrying a blood flow characterized by an internal pressure, an improvement comprising a pressure member for selectively applying an external pressure to the specified blood vessel in such a manner as substantially to balance the internal pressure of the blood flow.

2. A photoplethysmograph in accordance with claim 1, wherein the pressure member is disposed in such a manner as to apply pressure in a direction substantially normal to the body tissue.

3. In a photoplethysmograph for characterizing blood volume of the type having a light source and a detector disposed about a finger, the light source and a detector coupled to a ring for encircling the finger, an improvement comprising a pressure member for selectively applying external pressure to the specified blood vessel.

4. A photoplethysmograph in accordance with claim 3, wherein the pressure member is disposed in such a manner as to apply pressure in a direction substantially normal to the ring.

5. A photoplethysmograph in accordance with claim 3, wherein the pressure member is a set screw.

6. A monitoring system for monitoring a physiological characteristic of a patient, the monitoring system comprising:

a. a source of light disposed proximately to a region of body tissue of the patient;

b. at least one sensor for providing a signal based on detection of light through a specified blood vessel of the body tissue, the specified blood vessel carrying a blood flow characterized by an internal pressure; and

c. a pressure member in contact with and not encircling the region of body tissue for applying pressure through the region of tissue to the specified blood vessel in such a manner as substantially to balance the internal pressure of the blood flow.

7. In a photoplethysmograph for characterizing blood volume of the type having a first light source and a detector disposed about a region of body tissue containing a specified blood vessel, an improvement comprising a motion reference signal generator, the motion reference signal generator comprising:

a. a second light source disposed substantially proximally to the body tissue; and

b. a second detector located at a position distinct from that of the first detector for generating a motion signal.

8. A photoplethysmograph in accordance with claim 7, wherein the second detector is a photodetector for characterizing transmission through body tissue of illumination by the second light source.

9. A photoplethysmograph in accordance with claim 8, wherein the first and second light sources are identical.

10. A photoplethysmograph in accordance with claim 8, wherein the first and second light sources emit light having distinct spectral characteristics.

11. A method for obtaining contemporaneous plethysmographic and motion data with respect to a body member, the method comprising;

a. encircling the body member with a ring having at least one light source and at least two detectors;

b. deriving a plethysmographic signal from the first detector based on light transmission along a first path including a specified blood vessel; and

c. deriving a motion signal from the second detector based on light transmission along a second path.