Pulse oximetry data confidence indicator

• US 6,684,090 B2
• Filed: 05/15/2001
• Issued: 01/27/2004
• Est. Priority Date: 01/07/1999
• Status: Expired due to Term

• Current Assignee: Masimo Corporation
• Original Assignee: Masimo Corporation
• Inventors: Kiani, Massi E., Novak, Jerome J., Ali, Ammar Al, Breed, Divya S.
• Primary Examiner(s): Winakur; Eric F.
• Assistant Examiner(s): KREMER, MATTHEW J
• Application Number:
  US09/858,114
• Publication Number:
  US 20020035315A1
• Time in Patent Office: 987 Days
• Field of Search: 600/309-310,322-324,330,331,336
• US Class Current: 600/323
• CPC Class Codes: A61B 5/02416 using photoplethysmograph signals, e.g. generated by infrared radiation A61B5/14552 takes precedence
• CPC Class Codes: A61B 5/1455 using optical sensors, e.g. spectral photometrical oximeters
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/7207 of noise induced by motion artifacts
• CPC Class Codes: A61B 5/7214 using signal cancellation, e.g. based on input of two identical physiological sensors spaced apart, or based on two signals derived from the same sensor, for different optical wavelengths
• CPC Class Codes: A61B 5/7221 Determining signal validity, reliability or quality A61B5/7207 and A61B5/7217 take precedence
• CPC Class Codes: A61B 5/7405 using sound
• CPC Class Codes: A61B 5/746 Alarms related to a physiological condition, e.g. details of setting alarm thresholds or avoiding false alarms alarms per se G08B
• CPC Class Codes: G16Z 99/00 Subject matter not provided for in other main groups of this subclass

Abstract

An intelligent, rule-based processor provides a pulse indicator designating the occurrence of each pulse in a pulse oximeter-derived photo-plethysmograph waveform. When there is relatively no distortion corrupting the plethysmograph signal, the processor analyzes the shape of the pulses in the waveform to determine where in the waveform to generate the pulse indication. When distortion is present, looser waveform criteria are used to determine if pulses are present. If pulses are present, the pulse indication is based upon an averaged pulse rate. If no pulses are present, no indication occurs. The pulse indicator provides a trigger and amplitude output. The trigger output is used to initiate an audible tone “beep” or a visual pulse indication on a display, such as a vertical spike on a horizontal trace or a corresponding indication on a bar display. The amplitude output is used to indicate data integrity and corresponding confidence in the computed values of saturation and pulse rate. The amplitude output can vary a characteristic of the pulse indicator, such as beep volume or frequency or the height of the visual display spike.

The visual pulse indicator is supplemented by a signal quality alert. Combined with several indicators of signal quality, the alert is used to initiate a warning when data confidence is very low. The alert may be in the form of a message generated on the pulse oximeter display to warn that the accuracy of saturation and pulse rate measurements may be compromised. A confidence-based alarm utilizes signal quality measures to reduce the probability of false alarms when data confidence is low and to reduce the probability of missed events when data confidence is high.

Claims

1. A data confidence indicator comprising:

a plurality of physiological data and a plurality of signal quality measures derived from a physiological sensor output;

a plurality of comparator outputs each responsive to one of said measures and a corresponding one of a plurality of thresholds;

an alert trigger output combining said comparator outputs; and

a low signal quality warning generated in response to said alert trigger output, said thresholds set so that said warning occurs during a time period when there is low confidence in said data.

2. The indicator of claim 1 wherein said warning is a display message that supplements a visual pulse indicator, said display message specifying low signal quality when said visual pulse indicator has an amplitude less than one-third full-scale.

3. The indicator of claim 1 wherein said signal quality measures comprise at least one of an integrity measure, a pulse rate density measure and a harmonic ratio measure.

4. The indicator of claim 3 wherein said thresholds comprise an integrity value of less than 0.3, a pulse rate density value of less than 0.7 and a harmonic ratio value of less than 0.8.

5. The indicator of claim 1 further comprising:

a smoothing filter for said data;

an adjustment for said smoothing filter that is a function of at least one of said signal quality measures;

a predetermined alarm threshold for said data; and

an alarm trigger responsive to said smoothing filter and said alarm threshold.

6. The indicator of claim 5 wherein said filter comprises:

a buffer having said data as an input and a delay output, wherein the delay output comprises said data time-shifted according to said adjustment;

a first comparator output responsive to said data and said threshold; and

a second comparator output responsive to said delay output and said threshold, said comparator outputs combined so as to provide said alarm trigger.

7. A data confidence indicator comprising:

a processor configured to derive a time-dependent physiological data set and a plurality of time-dependent signal quality measures from a physiological signal;

a buffer configured to time-shift said data set by a delay to generate a delayed data set, said delay being a function of at least one of said signal quality measures;

a threshold setting a limit for said data set and said delayed data set; and

a warning generated when the levels of said data set and said delayed data set are beyond said threshold.

8. The data confidence indicator according to claim 7 further comprising:

a first comparator output responsive to said data set and said threshold;

a second comparator output responsive to said delayed data set and said threshold; and

a combination of said comparator outputs providing an alarm trigger for said warning.

9. The data confidence indicator according to claim 8 further comprising a combination of said signal quality measures providing an alert trigger to generate a warning when confidence in said data set is low.

10. A data confidence indication method comprising the steps of:

acquiring a signal from a physiological sensor;

calculating a physiological data set from said signal;

calculating a plurality of signal Quality measures from said signal;

indicating on a display a level of confidence in said data set based upon at least one of said signal quality measures;

utilizing said signal Quality measures to detect a low signal Quality period during which time said data set may be compromised;

writing an alert message on said display during at least a portion of said low signal quality period;

comparing each of said signal quality measures to a corresponding one of a plurality of thresholds to generate a plurality of trigger inputs; and

combining said trigger inputs to trigger a low signal quality warning.

11. A data confidence indication method comprising the steps of:

acquiring a signal from a physiological sensor;

calculating a physiological data set from said signal;

calculating a plurality of signal quality measures from said signal;

indicating on a display a level of confidence in said data set based upon at least one of said signal quality measures;

setting an alarm limit for said data set;

filtering said data set to generate an alarm trigger based upon said alarm limit; and

;

adjusting characteristics of said filtering step according to said signal quality measures so that more filtering is applied during said low signal quality period.

12. The data confidence indication method according to claim 11 wherein said filtering step comprises the substeps of:

time-shifting said data set to create a delayed data set;

comparing said data set to a threshold to generate a first trigger input;

comparing said delayed data set to said threshold to generate a second trigger input; and

combining said trigger inputs to generate said alarm trigger.

13. The data confidence indication method according to claim 12 wherein said adjusting comprises the substep of changing the amount of said time-shifting according to said signal quality measures.

14. A data confidence indication method comprising the steps of:

acquiring a signal from a physiological sensor;

calculating a physiological data set from said signal;

calculating a plurality of signal quality measures from said signal;

setting an alarm threshold for said data set; and

delaying an alarm trigger when said data set exceeds said threshold as a function of at least one of said signal Quality measures so as to reduce the probability of false alarms, wherein delaying the alarm trigger comprises;

time-shifting said data set by a delay to generate a delayed data set, wherein said delay is a function of at least one of said signal quality measures;

comparing said data set to said threshold to create a first limit output;

comparing said delayed data set to said threshold to create a second limit output; and

combining said limit outputs to generate said alarm trigger.

15. A data confidence indication method comprising the steps of:

acquiring a signal from a physiological sensor;

calculating a physiological data set from said signal;

calculating a plurality of signal quality measures from said signal;

setting an alarm threshold for said data set;

delaying an alarm trigger when said data set exceeds said threshold as a function of at least one of said signal quality measures so as to reduce the probability of false alarms;

comparing each of said signal quality measures to a corresponding one of a plurality of thresholds to generate a plurality of trigger inputs; and

combining said trigger inputs to trigger a low signal quality warning.