System and method of monitoring autoregulation

• US 10,292,663 B2
• Filed: 06/27/2016
• Issued: 05/21/2019
• Est. Priority Date: 06/30/2015
• Status: Active Grant

• Current Assignee: Covidien LP (Medtronic Plc)
• Original Assignee: Covidien LP (Medtronic Plc)
• Inventors: Addison, Paul S., Watson, James N.
• Primary Examiner(s): Winakur, Eric F
• Assistant Examiner(s): Liu, Chu Chuan
• Application Number:
  US15/194,122
• Publication Number:
  US 20170000423A1
• Time in Patent Office: 1,058 Days
• CPC Class Codes: A61B 5/0205 Simultaneously evaluating both cardiovascular conditions and different types of body conditions, e.g. heart and respiratory condition
• CPC Class Codes: A61B 5/021 Measuring pressure in heart or blood vessels A61B5/0205 takes precedence
• CPC Class Codes: A61B 5/02108 from analysis of pulse wave characteristics
• CPC Class Codes: A61B 5/022 by applying pressure to close blood vessels, e.g. against the skin; Ophthalmodynamometers
• CPC Class Codes: A61B 5/02255 the pressure being controlled by plethysmographic signals, e.g. derived from optical sensors
• CPC Class Codes: A61B 5/02416 using photoplethysmograph signals, e.g. generated by infrared radiation A61B5/14552 takes precedence
• CPC Class Codes: A61B 5/0285 Measuring or recording phase velocity of blood waves
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/14553 specially adapted for cerebral tissue
• CPC Class Codes: A61B 5/7221 Determining signal validity, reliability or quality A61B5/7207 and A61B5/7217 take precedence
• CPC Class Codes: A61B 5/7235 Details of waveform analysis A61B5/349 takes precedence
• CPC Class Codes: A61B 5/726 using Wavelet transforms
• CPC Class Codes: A61B 5/7278 Artificial waveform generation or derivation, e.g. synthesising signals from measured signals A61B5/327 takes precedence
• CPC Class Codes: A61B 5/7282 Event detection, e.g. detecting unique waveforms indicative of a medical condition A61B5/4094, A61B5/4818, A61B5/349, A61B5/0823 take precedence
• CPC Class Codes: A61B 5/742 using visual displays A61B5/339 takes precedence
• CPC Class Codes: G16H 50/20 for computer-aided diagnosis, e.g. based on medical expert systems
• CPC Class Codes: G16H 50/30 for calculating health indices; for individual health risk assessment
• CPC Class Codes: G16H 50/50 for simulation or modelling of medical disorders

Abstract

A method for monitoring autoregulation includes receiving a blood pressure signal and an oxygen saturation signal, determining a phase difference between the blood pressure signal and the oxygen saturation signal, and determining a patient'"'"'s autoregulation status based at least in part on a phase difference between the blood pressure signal and the oxygen saturation signal.

Claims

1. A method for monitoring autoregulation, the method comprising:

receiving, by a processor, a blood pressure signal of a patient;

receiving, by the processor, an oxygen saturation signal of the patient;

determining, by the processor, a phase difference between the blood pressure signal and the oxygen saturation signal;

determining, by the processor, a cerebral oximetry index (COx) value based on the blood pressure signal and the oxygen saturation signal;

determining, by the processor, a confidence level for the COx value based on the phase difference between the blood pressure signal and the oxygen saturation signal; and

determining, by the processor, an autoregulation status of the patient based at least in part on the confidence level determined based on the phase difference between the blood pressure signal and the oxygen saturation signal.

2. The method of claim 1, wherein determining the phase difference comprises processing the blood pressure signal and the oxygen saturation signal using a complex transform to determine the phase difference.

3. The method of claim 2, wherein the complex transform is a wavelet transform.

4. The method of claim 3, wherein the wavelet transform comprises a low oscillation Morlet wavelet with a central frequency of less than five radians per second.

5. The method of claim 1, wherein determining the phase difference comprises:

calculating a cross-wavelet transform of the blood pressure signal and the oxygen saturation signal, and

synchrosqueezing the cross-wavelet transform to generate a synchrosqueezed cross-wavelet transform indicative of the phase difference.

6. The method of claim 1, further comprising outputting, by the processor for display, a measure indicative of the autoregulation status of the patient.

7. The method of claim 1, further comprising providing an indication of impaired autoregulation status to an output device while the COx value is greater than zero and the phase difference is approximately equal to zero.

8. The method of claim 1, further comprising providing the COx value on a display while the COx value is zero or less than zero, and the phase difference is approximately +/−

π

radians, rapidly varying, or randomly distributed.

9. A non-transitory computer-readable medium having computer executable code stored thereon, the code comprising instructions to:

receive a blood pressure signal of a patient;

receive an oxygen saturation signal of the patient;

determine a phase difference between the blood pressure signal and the oxygen saturation signal;

determine a cerebral oximetry index (COx) value based on the blood pressure signal and the oxygen saturation signal;

determine a confidence level for the COx value based on the phase difference between the blood pressure signal and the oxygen saturation signal; and

determine an autoregulation status of the patient based at least in part on the confidence level determined based on the phase difference between the blood pressure signal and the oxygen saturation signal.

10. The non-transitory computer-readable medium of claim 9, wherein the instructions to determine the phase difference comprise instructions for applying a cross-wavelet transform to the blood pressure signal and the oxygen saturation signal to determine the phase difference.

11. The non-transitory computer-readable medium of claim 9, wherein the code further comprises instructions for providing an indication of impaired autoregulation status to an output device while the COx value is greater than zero and the phase difference is approximately equal to zero.

12. The non-transitory computer-readable medium of claim 9, wherein the instructions to determine the phase difference comprise:

instructions for calculating a cross-wavelet transform of the blood pressure signal and the oxygen saturation signal, and

instructions for synchrosqueezing the cross-wavelet transform to generate a synchrosqueezed cross-wavelet transform indicative of the phase difference.

13. A system for monitoring autoregulation, the system comprising:

an oxygen saturation sensor configured to obtain an oxygen saturation signal from a patient;

a controller comprising a processor configured to;

receive a blood pressure signal of the patient;

receive the oxygen saturation signal of the patient;

determine a phase difference between the blood pressure signal and the oxygen saturation signal;

determine a cerebral oximetry index (COx) value based on the blood pressure signal and the oxygen saturation signal;

determine a confidence level for the COx value based on the phase difference between the blood pressure signal and the oxygen saturation signal; and

determine autoregulation status of the patient based at least in part on the confidence level determined based on the phase difference between the blood pressure signal and the oxygen saturation signal.

14. The system of claim 13, further comprising a display, wherein the processor is configured to output an indication of the autoregulation status of the patient on the display.

15. The system of claim 13, wherein the processor is configured to:

calculate a cross-wavelet transform of the blood pressure signal and the oxygen saturation signal,

synchrosqueeze the cross-wavelet transform to generate a synchrosqueezed cross-wavelet transform, and

utilize the synchrosqueezed cross-wavelet transform to determine a confidence level related to the COx value.

16. The system of claim 13, wherein the controller is further configured to refrain from outputting, via a display, an indication of the autoregulation status of the patient when the phase difference does not corroborate the COx value.

17. The system of claim 13, wherein the controller is further configured to provide a visual or audible indication that the COx value is unavailable when the phase difference does not corroborate the COx value.

18. The system of claim 13, wherein the controller is further configured to hold or maintain the COx value immediately preceding a segment of the blood pressure signal or an oxygen saturation signal determined to be unreliable when the phase difference does not corroborate the COx value.

19. The system of claim 13, wherein the controller is further configured to present, via a display and when the phase difference does not corroborate the COx value, a most recent reliable COx value for a set period of time or until the phase difference indicates that a new COx value is reliable.

20. The system of claim 13, wherein the controller is further configured to:

determine an average COx value based on an unreliable COx value and a most recent reliable COx value; and

present, via a display, an indication of the average COx value when the phase difference does not corroborate the COx value.