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. 2021 Oct 12;21(20):6757.
doi: 10.3390/s21206757.

Heart and Lung Sound Measurement Using an Esophageal Stethoscope with Adaptive Noise Cancellation

Nourelhuda Mohamed  1 , Hyun-Seok Kim  2 , Kyu-Min Kang  3 , Manal Mohamed  1 , Sung-Hoon Kim  3 , Jae Gwan Kim  1
Affiliations

Heart and Lung Sound Measurement Using an Esophageal Stethoscope with Adaptive Noise Cancellation

Nourelhuda Mohamed et al. Sensors (Basel). .

Abstract

In surgeries where general anesthesia is required, the auscultation of heart and lung sounds is essential to provide information on the patient's cardiorespiratory system. Heart and lung sounds can be recorded using an esophageal stethoscope; however, there is huge background noise when this device is used in an operating room. In this study, a digital esophageal stethoscope system was designed. A 3D-printed case filled with Polydimethylsiloxane material was designed to hold two electret-type microphones. One of the microphones was placed inside the printed case to collect the heart and lung sound signals coming out from the patient through the esophageal catheter, the other was mounted on the surface of the case to collect the operating room sounds. A developed adaptive noise canceling algorithm was implemented to remove the operating room noise corrupted with the main heart and lung sound signals and the output signal was displayed on software application developed especially for this study. Using the designed case, the noise level of the signal was reduced to some extent, and by adding the adaptive filter, further noise reduction was achieved. The designed system is lightweight and can provide noise-free heart and lung sound signals.

Keywords: SIMULINK; adaptive noise canceling; digital esophageal stethoscope; esophageal catheter; least mean square.

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Conflict of interest statement

The authors declare that there are no conflict of interest regarding the publication of this paper.

Figures

Figure 1
Figure 1
Spectral intensity map of phonocardiographic records [12].
Figure 2
Figure 2
Sound absorption coefficient of the different samples according to [16].
Figure 3
Figure 3
General block diagram of an adaptive filter.
Figure 4
Figure 4
Basic concept of the digital esophageal stethoscope system.
Figure 5
Figure 5
Microphone case drawing (a,b) case filled with PDMS.
Figure 6
Figure 6
Resonance frequency of the casing.
Figure 7
Figure 7
Used microphone frequency characteristic curve.
Figure 8
Figure 8
Schematic diagram of the power amplifier circuit.
Figure 9
Figure 9
(a) Amplifier IC frequency response curve [22] and (b) power amplifier frequency response curve.
Figure 10
Figure 10
SIMULINK model: (a) block model designed to generate the simulated data and (b) LMS testing model.
Figure 11
Figure 11
Learning curve of the LMS adaptive filter used.
Figure 12
Figure 12
Different parts of the designed system. (a) Microphone case, (b) amplification circuit and (c) Teensy 3.2 development board.
Figure 13
Figure 13
Developed digital esophageal stethoscope system hardware.
Figure 14
Figure 14
System setup used while collecting and displaying the results.
Figure 15
Figure 15
(a) Main signal and its power spectral density; (b) noise signal and its power spectral density.
Figure 16
Figure 16
A graph showing sound frequency vs. sound level measured using the case (a) without PDMS material and (b) with PDMS material.
Figure 17
Figure 17
SIMULINK model result.
Figure 18
Figure 18
System experimental results displayed using the developed MATLAB app.
See this image and copyright information in PMC

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