PHOTOPLETHYSMOGRAPHY WITH CONTROLLED APPLICATION OF SENSOR PRESSURE

• US 20110046464A1
• Filed: 08/19/2009
• Published: 02/24/2011
• Est. Priority Date: 08/19/2009
• Status: Active Grant

• Current Assignee: Covidien LP (Medtronic Plc)
• Original Assignee: Nellcor Puritan Bennett LLC (Medtronic Plc)
• Inventors: Ostrowski, Rafael, Debreczeny, Martin P.
• Granted Patent: US 8,494,606 B2
• Time in Patent Office: Days
• US Class Current: 600/335
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/6826 Finger
• CPC Class Codes: A61B 5/6838 Clamps or clips
• CPC Class Codes: A61B 5/6843 Monitoring or controlling sensor contact pressure

Abstract

Systems, methods, and devices for obtaining consistently reproducible diagnostic measurements with a photoplethysmographic sensor are provided. In one embodiment, a method for obtaining such a diagnostic measurement includes applying a pressure between a photoplethysmographic sensor and a patient, increasing the pressure until the photoplethysmographic sensor outputs a plethysmographic waveform of minimal amplitude, decreasing the pressure by a predetermined fraction, and obtaining a diagnostic measurement using the photoplethysmographic sensor. The pressure may be applied using a pressure device that includes, for example, a clip, a wrap, an inflatable balloon or bladder, or an inflatable cuff or any combination thereof.

Claims

1. A method comprising:

applying a pressure between a photoplethysmographic sensor and a patient;

increasing the pressure until the photoplethysmographic sensor outputs a plethysmographic waveform of minimal amplitude;

decreasing the pressure by a predetermined fraction; and

obtaining a diagnostic measurement using the photoplethysmographic sensor.

2. The method of claim 1, wherein the predetermined fraction is approximately one half.

3. The method of claim 1, wherein the pressure is applied using a pressure device comprising a clip, a wrap, an inflatable balloon or bladder, or an inflatable cuff or any combination thereof.

4. The method of claim 1, wherein the pressure is applied using a pressure device controlled by an electronic patient monitor.

5. The method of claim 1, wherein the pressure is increased until the photoplethysmographic sensor outputs a waveform of minimal amplitude at a predetermined wavelength.

6. The method of claim 5, wherein the predetermined wavelength is suitable for a pulse oximetry measurement or for a measurement of total hemoglobin.

7. The method of claim 1, wherein the obtained diagnostic measurement comprises a pulse oximetry measurement or a measurement of total hemoglobin, or a combination thereof.

8. The method of claim 1, wherein decreasing the pressure by half comprises decreasing a pressure of between approximately 100 and 150 mm Hg to a pressure of between approximately 50 and 70 mm Hg.

9. A system comprising:

a photoplethysmographic sensor capable of application to a tissue site on a patient and capable of providing a plethysmographic signal associated with the patient;

a pressure device coupled to the photoplethysmographic sensor and capable of applying a pressure against the tissue site;

a pressure sensor coupled to the photoplethysmographic sensor and capable of indicating the pressure applied by the pressure device; and

an electronic patient monitor capable of receiving the plethysmographic signal and controlling the pressure device such that the applied pressure is a predetermined percentage of a maximal pressure, wherein the maximal pressure is a lowest applied pressure that causes the plethysmographic signal to reach a minimal amplitude.

10. The system of claim 9, wherein the pressure device comprises a clip, a wrap, an inflatable balloon or bladder, or an inflatable cuff, or any combination thereof.

11. The system of claim 9, wherein the pressure sensor comprises a piezo-resistive pressure sensor.

12. The system of claim 9, wherein the electronic patient monitor is capable of determining the maximal pressure by controlling the pressure device such that the applied pressure is increased until the plethysmographic signal reaches the minimal amplitude.

13. The system of claim 9, wherein the electronic patient monitor is capable of regularly determining the maximal pressure at a predetermined interval.

14. The system of claim 9, wherein the electronic patient monitor is capable of controlling the pressure device such that the applied pressure is between approximately 50 and 70 mm Hg when the maximal pressure is between approximately 100 and 150 mm Hg when the patient has a blood pressure in a normal range.

15. The system of claim 9, wherein the electronic patient monitor is capable of controlling the pressure device such that the applied pressure is the predetermined percentage of the maximal pressure when a diagnostic measurement based at least in part on the plethysmographic signal is being obtained.

16. The system of claim 9, wherein the electronic patient monitor is capable of controlling the pressure device such that the applied pressure is a low pressure that is less than the predetermined percentage of the maximal pressure when a diagnostic measurement based at least in part on the plethysmographic signal is not being obtained.

17. A method comprising:

measuring a first thickness of a photoplethysmographic sensor while attached around a patient tissue site at a minimal pressure;

compressing the photoplethysmographic sensor attached around the patient tissue site until a maximal pressure is reached, wherein the maximal pressure is a lowest pressure that causes the plethysmographic sensor to output a plethysmographic waveform of minimal amplitude;

measuring a second thickness of the photoplethysmographic sensor while attached around the patient tissue site at the maximal pressure;

decompressing the photoplethysmographic sensor attached around the patient tissue site until the photoplethysmographic sensor has an intermediate thickness between the first thickness and the second thickness, wherein the intermediate thickness is a predetermined fractional distance between the first and second thickness; and

obtaining a diagnostic measurement of interest using the photoplethysmographic sensor.

18. The method of claim 17, wherein the method is performed while the photoplethysmographic sensor is attached to the patient tissue site, wherein the photoplethysmographic sensor comprises a finger clip.

19. The method of claim 17, wherein the method is performed using the photoplethysmographic sensor, wherein the photoplethysmographic sensor is configured to perform the method based on control signals from an electronic patient monitor.

20. A method comprising:

applying a first pressure to a patient tissue site such that arterial blood flow in the patient tissue site substantially stops;

applying a second pressure to the patient tissue site such that a majority of extravascular fluid normally present in the patient tissue site is not present in the patient tissue site while a majority of arterial blood normally present in the patient tissue site remains in the patient tissue site, wherein the second pressure is approximately half of the first pressure; and

obtaining a diagnostic measurement using a photoplethysmographic sensor at the patient tissue site while the second pressure is being applied.

21. The method of claim 20, wherein applying the first pressure comprises applying a lowest pressure that causes a plethysmographic signal from the photoplethysmographic sensor to reach a minimal amplitude.

22. The method of claim 20, wherein the first pressure and the second pressure are applied by a pressure device on the photoplethysmographic sensor, wherein the pressure device is controlled by an electronic patient monitor.

23. The method of claim 20, wherein the obtained diagnostic measurement comprises a pulse spectrum measurement for pulse oximetry.

24. The method of claim 20, wherein the obtained diagnostic measurement comprises a pulse spectrum measurement for determination of total hemoglobin.

25. A photoplethysmographic sensor comprising:

a pressure device capable of applying pressure between the photoplethysmographic sensor and a patient; and

a pressure sensor capable of determining the applied pressure.

26. The sensor of claim 25, wherein the pressure device comprises an adjustable clip, a wrap, an inflatable balloon or bladder, or an inflatable cuff, or any combination thereof.

27. The sensor of claim 25, wherein the pressure device is capable of varying the applied pressure based on a signal from a pulse oximetry patient monitor.

28. The sensor of claim 25, wherein the pressure device is capable of applying a pressure sufficient to cause a plethysmographic signal from the photoplethysmographic sensor to decrease to a minimum.

29. The sensor of claim 25, wherein the photoplethysmographic sensor is a reflectance-type photoplethysmographic sensor.

30. The sensor of claim 25, wherein the photoplethysmographic sensor is a transmission-type photoplethysmographic sensor.