Adaptive Acoustic Signal Filtering for Respiration Monitoring System

• US 20140135639A1
• Filed: 11/13/2012
• Published: 05/15/2014
• Est. Priority Date: 11/13/2012
• Status: Abandoned Application

• Current Assignee: Sharp Laboratories of America Incorporated (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Yongji Fu, Yungkai Kyle Lai
• Inventors: LAI, Yungkai Kyle, FU, Yongji
• Application Number:
  US13/675,014
• Publication Number:
  US 20140135639A1
• Time in Patent Office: Days
• US Class Current: 600/529
• CPC Class Codes: A61B 5/0803 Recording apparatus specially adapted therefor
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: A61B 5/7225 Details of analog processing, e.g. isolation amplifier, gain or sensitivity adjustment, filtering, baseline or drift compensation A61B5/30, A61B5/316 take precedence; transformers for specific applications H01F38/00; amplifiers H03F

Abstract

An adaptive acoustic signal filter for a respiration monitoring system includes a filter stage and a cutoff frequency adapter. The filter stage applies a cutoff frequency to an input acoustic signal waveform containing respiration and heart sound components in a filtering operation to produce a filtered acoustic signal waveform from which heart sound components have been removed. The adapter then performs cutoff frequency optimization tests on the filtered signal waveform and determines from the tests whether adjustment of the cutoff frequency is indicated. These tests assess whether the filtering operation struck a proper balance between removing heart sound components and preserving respiration sound components in the filtered signal waveform. If adjustment of the cutoff frequency is indicated, the adapter adjusts the cutoff frequency and the adjusted cutoff frequency is provided to the filter stage for application in a next filtering operation performed on the input signal waveform.

Claims

1. An adaptive acoustic signal filter for a respiration monitoring system, comprising:

a filter stage configured to apply a cutoff frequency to an input acoustic signal waveform containing respiration and heart sounds in a filtering operation to produce a filtered acoustic signal waveform from which heart sounds have been removed; and

a cutoff frequency adapter operatively coupled with the filter stage and configured to perform one or more cutoff frequency optimization tests on the filtered signal, determine from the tests whether adjustment of the cutoff frequency is indicated and selectively adjust the cutoff frequency and provide the adjusted cutoff frequency to the filter stage for application in a next filtering operation performed on the input signal waveform depending on whether adjustment of the cutoff frequency is indicated.

2. The filter of claim 1, wherein the cutoff frequency optimization tests assess whether the filtering operation struck a proper balance between removing heart sounds and preserving respiration sounds in the filtered signal waveform.

3. The filter of claim 1, wherein the cutoff frequency optimization tests comprise a test of residual heart sound presence in the filtered signal waveform.

4. The filter of claim 3, wherein the residual heart sound presence test determines whether actual times between peaks in the filtered signal waveform fall within a range of expected times between heartbeats.

5. The filter of claim 1, wherein the cutoff frequency optimization tests comprise a test of slopes of peaks in the filtered signal waveform.

6. The filter of claim 1, wherein the cutoff frequency optimization tests comprise a test of smoothness of the filtered signal waveform.

7. The filter of claim 1, wherein the cutoff frequency is adjusted using a monotonously decreasing function.

8. The filter of claim 1, wherein the filter is a lowpass filter.

9. The filter of claim 1, wherein the input signal waveform comprises an energy envelope computed from a raw acoustic signal.

10. The filter of claim 1, wherein the filter stage and the cutoff frequency adapter comprise software instructions executed by a processor.

11. An adaptive acoustic signal filtering method for a respiration monitoring system, comprising the steps of:

applying by the system to an input acoustic signal waveform containing respiration and heart sounds in a filtering operation a cutoff frequency to produce a filtered acoustic signal waveform from which heart sounds have been removed;

performing by the system one or more cutoff frequency optimization tests on the filtered signal waveform;

determining by the system from the tests whether adjustment of the cutoff frequency is indicated; and

selectively adjusting by the system the cutoff frequency and providing by the system the adjusted cutoff frequency to the filter for application in a next filtering operation performed on the input signal waveform depending on whether adjustment of the cutoff frequency is indicated.

12. The method of claim 11, wherein the cutoff frequency optimization tests assess whether the filtering operation struck a proper balance between removing heart sounds and preserving respiration sounds in the filtered signal waveform.

13. The method of claim 11, wherein the cutoff frequency optimization tests comprise a test of residual heart sound presence in the filtered signal waveform.

14. The method of claim 13, wherein the residual heart sound presence test determines whether actual times between peaks in the filtered signal waveform fall within a range of expected times between heartbeats.

15. The method of claim 11, wherein the cutoff frequency optimization tests comprise a test of slopes of peaks in the filtered signal waveform.

16. The method of claim 11, wherein the cutoff frequency optimization tests comprise a test of smoothness of the filtered signal waveform.

17. The method of claim 11, wherein the cutoff frequency is adjusted using a monotonously decreasing function.

18. The method of claim 11, wherein the filter is a lowpass filter.

19. The method of claim 11, wherein the input signal waveform comprises an energy envelope computed from a raw acoustic signal.

20. The method of claim 11, wherein the method is performed at least in part by executing software instructions under processor control.