Determination of a physiological parameter

• US 8,923,945 B2
• Filed: 09/13/2010
• Issued: 12/30/2014
• Est. Priority Date: 09/24/2009
• Status: Active Grant

• Current Assignee: Covidien LP (Medtronic Plc)
• Original Assignee: Covidien LP (Medtronic Plc)
• Inventors: McKenna, Edward M.
• Primary Examiner(s): Winakur, Eric
• Assistant Examiner(s): Liu, Chu Chuan (JJ)
• Application Number:
  US12/880,303
• Publication Number:
  US 20110071366A1
• Time in Patent Office: 1,569 Days
• Field of Search: 600/310, 600/322, 600/323, 600/324, 600/331, 600/473, 600/476, 600/336, 356/41
• US Class Current: 600/336
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/726 using Wavelet transforms
• CPC Class Codes: G06T 11/206 Drawing of charts or graphs

Abstract

Methods and systems are provided for transmitting and receiving photon density waves to and from tissue, and processing the received waves using wavelet transforms to identify non-physiological signal components and/or identify physiological conditions. A pulse oximeter may receive the photon density waves from the tissue to generate a signal having phase and amplitude information. A phase signal may be proportional to a scattering by total particles in the tissue, and an amplitude signal may correlate to an absorption by certain particles, providing information on a ratio of different particles in the tissue. Processing the phase and amplitude signals with wavelet transforms may enable an analysis of signals with respect to time, frequency, and magnitude, and may produce various physiological data. For example, non-physiological noise components may be identified, and certain physiological conditions may be identified by processing scalograms of the original signals with patterns corresponding to certain physiological conditions.

Claims

1. A monitor, comprising:

a display;

a connector port configured to receive a signal generated in response to propagation of photon density waves through tissue; and

data processing circuitry configured to;

derive a phase signal and a plethysmography signal from the received signal, wherein changes the phase signal are indicative of changes in photon scattering and changes in the plethysmography signal are indicative of changes in absorption of photons by the tissue;

apply a continuous wavelet transform to the phase signal and to the plethysmography signal to generate a phase signal scalogram and a plethysmography signal scalogram, respectively;

compare the phase signal scalogram and the plethysmography signal scalogram;

identify temporal correlations between changes in photon scattering and changes in absorption of photons by the tissue based on the comparison of the phase signal scalogram and the plethysmography signal scalogram;

distinguish physiological and non-physiological components of the signal based on the temporal correlations between changes in photon scattering and changes in absorption of photons by the tissue, wherein physiological components are identified at temporal locations where changes in photon scattering correlate to changes in absorption of photons by the tissue, and non-physiological components are identified at temporal locations where changes in photon scattering do not correlate to changes in absorption of photons by the tissue;

generate patient physiological data based on at least the physiological components of the signal; and

display the patient physiological data on the display.

2. The monitor, as set forth in claim 1, wherein the monitor is configured to estimate a total number of scattering particles.

3. The monitor, as set forth in claim 1, wherein the monitor is configured to estimate oxygen saturation based on the physiological component of the signal.

4. The monitor of claim 1, wherein the photon density waves are modulated at a frequency of between approximately 50 MHz to 3 GHz prior to propagation through the tissue.

5. A monitoring system, comprising:

a sensor configured to acquire photon density wave data when positioned on a patient; and

a monitor in communication with the sensor, wherein the monitor is configured to;

receive the photon density wave data from the sensor;

derive a phase signal and a plethysmography signal from the photon density wave data, wherein changes in the phase signal correspond to photon scattering and changes in the plethysmography signal correspond to absorption of photons by tissue of the patient;

apply a continuous wavelet transform to the phase signal and to the plethysmography signal to generate a phase signal scalogram and a plethysmography signal scalogram, respectively;

compare the phase signal scalogram to the plethysmography signal scalogram;

distinguish between physiological and non-physiological aspects of the photon density wave data based on whether the comparison indicates that changes in photon scattering temporally correlate with changes in absorption of photons by the tissue, wherein physiological aspects are identified at temporal locations where changes in photon scattering correlate to changes in absorption of photons by the tissue, and non-physiological aspects are identified at temporal locations where changes in photon scattering do not correlate to changes in absorption of photons by the tissue.

6. The monitoring system of claim 5, wherein the photon density wave data comprises information relating to a total number of particles at a tissue site where the sensor is positioned on the patient and information relating to a ratio of different types of particles at the tissue site.

7. The monitoring system of claim 5, wherein the monitor is configured to identify a physiological condition based on at least the physiological aspect of the photon density wave data.

8. The monitoring system of claim 5, comprising an emitter and a modulator configured to modulate light emitted by the emitter to generate photon density waves.

9. The monitoring system of claim 5, wherein the monitor is configured to remove the non-physiological aspects from the photon density wave data.

10. The monitoring system of claim 5, wherein the monitor is configured to estimate oxygen saturation based on the physiological aspects of the photon density wave data.

11. The monitoring system of claim 5, comprising a modulator disposed in the monitor or in the sensor, wherein the modulator is configured to modulate light emitted by an emitter of the sensor at a frequency between approximately 50 MHz to 3 GHz to generate resolvable photon density waves.