Detecting a probe-off event in a measurement system

• US 8,696,585 B2
• Filed: 09/30/2008
• Issued: 04/15/2014
• Est. Priority Date: 09/30/2008
• Status: Active Grant

• Current Assignee: Nellcor Puritan Bennett Ireland
• Original Assignee: Nellcor Puritan Bennett Ireland
• Inventors: Addison, Paul Stanley, Watson, James Nicholas
• Primary Examiner(s): Blumel, Benjamin P
• Application Number:
  US12/242,894
• Publication Number:
  US 20100081898A1
• Time in Patent Office: 2,023 Days
• Field of Search: None
• US Class Current: 600/500
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/6843 Monitoring or controlling sensor contact pressure
• CPC Class Codes: A61B 5/726 using Wavelet transforms
• CPC Class Codes: G06V 10/52 Scale-space analysis, e.g. wavelet analysis multi-scale boundary representations G06V10/42

Abstract

According to embodiments, techniques for detecting probe-off events are disclosed. A sensor or probe may be used to obtain a plethysmograph or photoplethysmograph (PPG) signal from a subject. A wavelet transform of the signal may be performed and a scalogram may be generated based at least in part on the wavelet transform. One or more characteristics of the scalogram may be determined. The determined characteristics may include, for example, an energy decrease, a broadscale high-energy cone, a regular, repeated high-scale pattern, a low-scale information pattern; and a pulse band. The absence or presence of these and other characteristics, along with information about the characteristics, may be analyzed to detect a probe-off event. A confidence indicator may be calculated in connection with probe-off event detections and alarms may be generated when probe-off events occur.

Claims

1. A method of detecting a probe-off event comprising:

obtaining a signal;

generating, using processing equipment, a wavelet transform based at least in part on the signal;

generating, using the processing equipment, a scalogram based at least in part on the wavelet transform;

determining, using the processing equipment, one or more characteristics from the scalogram;

analyzing, using the processing equipment, the one or more characteristics; and

detecting, using the processing equipment, a probe-off event based at least in part on the one or more characteristics.

2. The method of claim 1, wherein obtaining the signal comprises obtaining a PPG signal.

3. The method of claim 1, further comprising quantizing, using the processing equipment, the scalogram prior to determining the one or more characteristics.

4. The method of claim 1, wherein determining the one or more characteristics comprises detecting, using the processing equipment, the presence or absence of the one or more characteristics in the scalogram.

5. The method of claim 4, further comprising:

detecting, using the processing equipment, regularity in the scalogram at one or more times prior to the presence of a characteristic; and

detecting, using the processing equipment, non-regularity in the scalogram at one or more times subsequent to the presence of the characteristic.

6. The method of claim 5, wherein the one or more characteristics comprise characteristics selected from the group consisting of an energy decrease, a broadscale high-energy cone, a regular, repeated high-scale pattern, a low-scale information pattern, a pulse band, and combinations thereof.

7. The method of claim 6, wherein detecting the presence of the broadscale high-energy cone comprises:

calculating, using the processing equipment, energy within a first region of the scalogram over time;

calculating, using the processing equipment, energy within a second region of the scalogram over time; and

detecting, using the processing equipment, a change in the energy calculated in the second region compared to the energy calculated in the first region.

8. The method of claim 6, wherein detecting the probe-off event comprises detecting the probe-off event when a broadscale high-energy cone is detected and at least one of the following events occurs:

an energy decrease is detected;

a regular repeating high-scale pattern is absent after the occurrence of the broadscale high energy cone;

a low-scale information pattern is absent after the occurrence of the broadscale high energy cone; and

the pulse band is absent after the occurrence of the broadscale-high energy cone.

9. The method of claim 1, further comprising calculating, using the processing equipment, a confidence indicator related to the probe-off event.

10. A system for detecting a probe-off event comprising:

a processor configured to perform operations comprising;

obtaining a signal;

generating a wavelet transform based at least in part on the signal;

generating a scalogram based at least in part on the wavelet transform;

determining one or more characteristics from the scalogram;

analyzing the one or more characteristics; and

detecting a probe-off event based at least in part on the one or more characteristics.

11. The system of claim 10, wherein obtaining the signal comprises obtaining a PPG signal.

12. The system of claim 10, wherein the processor is further configured to quantize the scalogram prior to determining the one or more characteristics.

13. The system of claim 10, wherein determining the one or more characteristics comprises detecting the presence or absence of the one or more characteristics in the scalogram.

14. The system of claim 13, wherein the processor is further configured to perform operations comprising:

detecting regularity in the scalogram at one or more times prior to the presence of a characteristic; and

detecting non-regularity in the scalogram at one or more times subsequent to the presence of the characteristic.

15. The system of claim 14, wherein the one or more characteristics comprise characteristics selected from the group consisting of an energy decrease, a broadscale high-energy cone, a regular, repeated high-scale pattern, a low-scale information pattern, a pulse band, and combinations thereof.

16. The system of claim 15, wherein detecting the presence of the broadscale high-energy cone comprises:

calculating energy within a first region of the scalogram over time;

calculating energy within a second region of the scalogram over time; and

detecting a change in the energy calculated in the second region compared to the energy calculated in the first region.

17. The system of claim 15, wherein detecting the probe-off event comprises detecting the probe-off event when a broadscale high-energy cone is detected and at least one of the following events occurs:

an energy decrease is detected;

a regular repeating high-scale pattern is absent after the occurrence of the broadscale high energy cone;

a low-scale information pattern is absent after the occurrence of the broadscale high energy cone; and

the pulse band is absent after the occurrence of the broadscale-high energy cone.

18. The system of claim 10, wherein the processor is further configured to calculate a confidence indicator related to the probe-off event.

19. A non-transitory computer-readable medium for detecting a probe-off event, the computer-readable medium having computer program instructions recorded thereon for:

obtaining a signal;

generating a wavelet transform based at least in part on the signal;

generating a scalogram based at least in part on the wavelet transform;

determining one or more characteristics from the scalogram;

analyzing the one or more characteristics; and

detecting a probe-off event based at least in part on the one or more characteristics.

20. The non-transitory computer-readable medium of claim 19, having further computer program instructions for determining the one or more characteristics at least in part by detecting the presence or absence of the one or more characteristics in the scalogram.