Pulse oximeter probe-off detector

• US 20040158134A1
• Filed: 11/25/2003
• Published: 08/12/2004
• Est. Priority Date: 03/25/1999
• Status: Active Grant

• Current Assignee: Ammar A.L. Ali, Mohamed K. Diab
• Original Assignee: Ammar A.L. Ali, Mohamed K. Diab
• Inventors: Diab, Mohamed K., Ali, Ammar Al
• Granted Patent: US 7,471,969 B2
• Time in Patent Office: Days
• US Class Current: 600/323
• CPC Class Codes: A61B 2560/0276 Determining malfunction
• 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 5/7221 Determining signal validity, reliability or quality A61B5/7207 and A61B5/7217 take precedence

Abstract

A processor provides signal quality based limits to a signal strength operating region of a pulse oximeter. These limits are superimposed on the typical gain dependent signal strength limits. If a sensor signal appears physiologically generated, the pulse oximeter is allowed to operate with minimal signal strength, maximizing low perfusion performance. If a sensor signal is potentially due to a signal induced by a dislodged sensor, signal strength requirements are raised. Thus, signal quality limitations enhance probe off detection without significantly impacting low perfusion performance. One signal quality measure used is pulse rate density, which defines the percentage of time physiologically acceptable pulses are occurring. If the detected signal contains a significant percentage of unacceptable pulses, the minimum required signal strength is raised proportionately. Another signal quality measure used in conjunction with pulse rate density is energy ratio, computed as the percentage of total energy contained in the pulse rate fundamental and associated harmonics.

Claims

1. A probe-off detector providing an indication that a physiological sensor may not be properly positioned proximate a tissue site, said probe-off detector comprising:

a signal quality input that defines an acceptable operating region for the sensor;

a signal strength calculator comprising

an input in communications with a sensor signal from a sensor; and

a signal strength output dependent on a time-varying component of the sensor signal;

a stored relationship between the signal strength output and the signal quality input; and

probe-off logic providing a probe-off output based on a comparison of the signal strength output and the signal quality input with said stored relationship.

2. The probe-off detector of claim 1, wherein the probe-off logic comprises a comparator.

3. The probe-off detector of claim 1, wherein the probe-off logic comprises an energy ratio check.

4. The probe-off detector of claim 1, wherein the probe-off logic comprises a time check indicating that no acceptable pulses have occurred for a sufficient time period.

5. A method of detecting that a pulse oximetry sensor may not be properly attached to a tissue site by processing a sensor signal, the method comprising:

determining a signal strength limit dependent on a processor input;

calculating a signal strength value from a sensor signal of a pulse oximetry sensor;

calculating a signal quality value of the sensor signal; and

indicating a probe-off condition when the signal strength value is below the signal strength limit for the signal quality value.

6. The method of claim 5, wherein the processor input comprises a sensitivity mode.

7. A detector for determining when a physiological sensor may not be properly positioned with respect to a measurement site, the detector comprising:

a signal strength calculator which processes an input signal expected to be representative of at least one parameter measured by a physiological sensor, to produce an output representative of a strength of the input signal; and

logic which indicates that the input signal may not represent the parameter when a predetermined portion of the output is below a threshold value.

8. The detector of claim 7, wherein the threshold value comprises a floor value below which a probe-off condition exists for all values of the output.

9. A method of determining whether a pulse oximetry sensor is properly connected to a patient, said method comprising the steps of:

receiving a signal strength vector;

receiving at least one of a signal strength limit and a pulse rate density;

providing an indication of poor signal strength based on said signal strength vector and said at least one of a signal strength limit and a pulse rate density; and

determining whether a pulse oximetry sensor is properly connected to a patient based at least in part on the indication.

10. The method of claim 9,

wherein said at least one of said signal strength limit and said pulse rate density includes said signal strength limit, and

wherein said providing the indication further comprises determining a relationship between a signal strength scalar and said signal strength limit, wherein said signal strength scalar is based upon said signal strength vector.

11. The method of claim 10, wherein said determining a relationship between a signal strength scalar and said signal strength limit comprises determining whether said signal strength scalar is greater than or equal to said signal strength limit.

12. The method of claim 9,

wherein said at least one of said signal strength limit and said pulse rate density includes said pulse rate density, and

wherein said providing the indication further comprises determining a relationship between a signal strength scalar and said pulse rate density, wherein said signal strength scalar is based upon said signal strength vector.

13. The method of claim 12, wherein said determining a relationship between a signal strength scalar and said pulse rate density comprises determining whether said pulse rate density is greater than a function of said signal strength scalar.

14. The method of claim 13, wherein said function is of the form y=mx+b and wherein b comprises said signal strength scalar.

15. The method of claim 14, wherein m is approximately −

0.1.30.

16. The method of claim 14, wherein b is approximately 0.53.

17. The method of claim 9, further comprising providing an indication of signal strength failure based on said signal strength vector and said at least one of a signal strength limit and a pulse rate density;

and

wherein said determining further comprises determining whether the pulse oximetry sensor is properly connected to the patient based on at least one of the indication of poor signal strength and the indication of signal strength failure.

18. The method of claim 17, wherein said providing the indication of signal strength failure further comprises determining a relationship between a signal strength scalar and a floor value, wherein said signal strength scalar is based upon said signal strength vector.

19. The method of claim 18, wherein said determining a relationship comprises determining whether said signal strength scalar is greater than or equal to said floor value.

20. The method of claim 19, wherein said floor value is approximately 0.02.