Pulse oximeter with separate ensemble averaging for oxygen saturation and heart rate

• US 20050197793A1
• Filed: 03/08/2004
• Published: 09/08/2005
• Est. Priority Date: 03/08/2004
• Status: Active Grant

• Current Assignee: Covidien LP (Medtronic Plc)
• Original Assignee: Nellcor Puritan Bennett Incorporated (Medtronic Plc)
• Inventors: Baker, Clark R. Jr.
• Granted Patent: US 7,039,538 B2
• Time in Patent Office: Days
• US Class Current: 702/78
• 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 5/725 using specific filters therefor, e.g. Kalman or adaptive filters A61B5/316 take precedence

Abstract

The use of two separate ensemble averagers for processing a detected waveform for use in calculating oxygen saturation and a pulse rate. The ensemble averager used for calculating oxygen saturation operates on a signal which has been normalized, while the ensemble averager for the pulse rate calculation operates on a signal which has not been normalized. The metrics chosen for the two paths through the two ensemble averagers can be varied to optimize the ensemble averaging for oxygen saturation or pulse rate calculations.

Claims

1. A method for processing signals in a pulse oximeter to determine oxygen saturation and pulse rate, comprising:

receiving waveforms corresponding to two different wavelengths of light from a patient;

ensemble averaging said waveforms in a first ensemble averager;

calculating a pulse rate based on an output of said first ensemble averager;

normalizing said waveforms to produce normalized waveforms;

ensemble averaging said normalized waveforms in a second ensemble averager; and

calculating an oxygen saturation based on an output of said second ensemble averager.

2. The method of claim 1 further comprising:

said ensemble averaging using variable weights;

selecting first metrics for said first ensemble averager to optimize said calculating a pulse rate; and

selecting second metrics for said second ensemble averager to optimize said calculating an oxygen saturation.

3. The method of claim 2 wherein said first and second metrics both include an arrhythmia metric for detecting an arrhythmic pulse, said arrhythmia metric for said first metrics, in connection with calculating a pulse rate, having a lower associated threshold for recognizing arrhythmia than said arrhythmic metric for said second metrics.

4. The method of claim 2 wherein said first and second metrics both include a short term metric which is a measure of short-term changes in pulse amplitude;

said first ensemble averager increasing an ensemble averaging weight in response to a short-term decrease in pulse amplitude faster than said second ensemble averager.

5. A pulse oximeter for determining oxygen saturation and pulse rate, comprising:

a detector which receives waveforms corresponding to two different wavelengths of light from a patient;

a first ensemble averager;

a pulse rate calculator, coupled to an output of said first ensemble averager;

a normalizer coupled to said detector for normalizing said waveforms to produce normalized waveforms;

a second ensemble averager; and

an oxygen saturation calculator coupled to an output of said second ensemble averager.

6. The pulse oximeter of claim 5 further comprising:

wherein said ensemble averagers are configured to ensemble average using variable weights;

a signal quality metric calculator configured to provide first metrics for said first ensemble averager to optimize said calculating a pulse rate, and second metrics for said second ensemble averager to optimize said calculating an oxygen saturation.

7. A method for processing signals in a pulse oximeter to determine oxygen saturation and pulse rate, comprising:

receiving waveforms corresponding to two different wavelengths of light from a patient;

low pass filtering said waveforms in a first low pass filter;

calculating a pulse rate based on an output of said first low pass filter;

normalizing said waveforms to produce normalized waveforms;

low pass filtering said normalized waveforms in a second low pass filter; and

calculating an oxygen saturation based on an output of said second low pass filter.

8. The method of claim 7 further comprising:

selecting first metrics for said first low pass filter to optimize said calculating a pulse rate; and

selecting second metrics for said second low pass filter to optimize said calculating an oxygen saturation.

9. The method of claim 8 wherein:

the low-pass filtering weight associated with said first low pass filter is based on a frequency ratio metric which quantifies the frequency-content of said waveforms relative to a pulse-rate estimate.

10. The method of claim 8 wherein:

a low-pass filtering weight for said second low pass filter is based on

a frequency ratio metric which quantifies the frequency-content of said waveforms relative to a pulse-rate estimate that metric, and

a separate Ratio-of-Ratios variance metric.

11. A method for processing signals in a pulse oximeter to determine oxygen saturation and pulse rate, comprising:

receiving waveforms corresponding to two different wavelengths of light from a patient;

low pass filtering and ensemble averaging said waveforms in a first low pass filter and ensemble averager;

calculating a pulse rate based on an output of said first low pass filter and ensemble averager;

normalizing said waveforms to produce normalized waveforms;

low pass filtering and ensemble averaging said normalized waveforms in a second low pass filter and ensemble averager; and

calculating an oxygen saturation based on an output of said second low pass filter and ensemble averager.

12. A pulse oximeter for determining oxygen saturation and pulse rate, comprising:

a detector which receives waveforms corresponding to two different wavelengths of light from a patient;

a first low pass filtering;

a pulse rate calculator, coupled to an output of said first low pass filter;

a normalizer coupled to said detector for normalizing said waveforms to produce normalized waveforms;

a second low pass filter; and

an oxygen saturation calculator coupled to an output of said second low pass filter.

13. The pulse oximeter of claim 12 further comprising:

wherein said low pass filters are configured to ensemble average using variable weights;

a signal quality metric calculator configured to provide first metrics for said first low pass filter to optimize said calculating a pulse rate, and second metrics for said second low pass filter to optimize said calculating an oxygen saturation.

14. The pulse oximeter of claim 12 wherein:

the low-pass filtering weight associated with said first low pass filter is based on a frequency ratio metric which which quantifies the frequency-content of said waveforms relative to a pulse-rate estimate.

15. The pulse oximeter of claim 12 wherein:

a low-pass filtering weight for said second low pass filter is based on

a frequency ratio metric which which quantifies the frequency-content of said waveforms relative to a pulse-rate estimate that metric, and

a separate Ratio-of-Ratios variance metric.

16. A pulse oximeter for determining oxygen saturation and pulse rate, comprising:

a detector which receives waveforms corresponding to two different wavelengths of light from a patient;

a first low pass filtering and ensemble averager;

a pulse rate calculator, coupled to an output of said first low pass filter and ensemble averager;

a normalizer coupled to said detector for normalizing said waveforms to produce normalized waveforms;

a second low pass filter and ensemble averager; and

an oxygen saturation calculator coupled to an output of said second low pass filter and ensemble averager.

17. A method for processing signals in a pulse oximeter to determine oxygen saturation, comprising:

receiving waveforms corresponding to two different wavelengths of light from a patient;

processing a new waveform after a pulse period trigger to ensemble average with a historical average waveform; and

when said new waveform differs from said historical average waveform by more than a predetermined threshold, interpolating between the new waveform and the historical average waveform for a first few samples of a new, composite historical average waveform.

18. The method of claim 17 wherein said first few samples are four samples, and said interpolations are at 80%, 60%, 40%, and 20% of the difference between the new waveform and the historical average waveform.