The Electronic Esophageal StethoscopeJoseph H. McIsaac, III, MD, MS, Hartford Hospital Anesthesiology

Megan Bowers, University of Connecticut School of Engineering

Stuart Chen, University of Illinois at Urbana-Champaign

Esophageal Stethoscope: An Overview

Used to monitor anesthetized patients.

Greater amplitude of heart and lung sounds than with precordial stethoscope.

Room for Change

Use of esophageal stethoscope criticized for its subjectivity.

No standard method exists for recording heart and lung diagnoses during surgery.

Continuous auscultation difficult in modern OR setting.

Project Goals

Device for safe OR recording.

Software program to record patient sounds and remove ambient room noise.

Visual representation of heart and lung sounds.

Automated diagnostic ability.

Discussion of Results

LabVIEWTM successfully records high-quality stereo .wav files in OR.

Signal subtraction in LabVIEWTM is not satisfactory for removing ambient room noise.

Wavelet analysis holds the most promise for a noise cancellation algorithm for this application.

Short-Term Goals

Amplify patient sounds.Employ noise cancellation algorithm

such as wavelet analysis to improve quality of patient sounds.

Develop a method of visual representation of heart and lung sounds.

Future Plans

Refine hardware and software designs.Program the recording software to

automatically diagnose the incoming heart and lung sounds.

Produce a marketable device to eliminate the subjectivity currently associated with the esophageal stethoscope.

References1. Manecke GR et al. Auscultation revisited: The waveform and

spectral characteristics of breath sounds during general anesthesia. J Clin Monit, 14:231-240, 1997.

2. Kim D, Tavel ME. Assessment of severity of aortic stenosis through time-frequency analysis of murmur. Chest. 124(5):1638-44, 2003.

3. Liatsos C, et al. Bowel sounds analysis: a novel noninvasive method for diagnosis of small-volume ascites. Dig Dis Sci. 48(8):1630-6, 2003.

4. St. Clair C, McIsaac J. The Electronic Esophageal Stethoscope: New Analysis of Heart and Lung Sounds, 2002.

5. Geaney L, McIsaac J. The Electronic Esophageal Stethoscope: The Frequency Response of the Esophageal Stethoscope, 2003.

6. Charbonneu G et al. Basic Techniques for respiratory sound analysis. European Respiratory Review. 10:77, 625-635, 2000.

Stuart ChenDave KaputaDr. Newton DeFaria

Acknowledgements

Step 3: System Characterization

Test frequency response of adult esophageal stethoscope at all frequencies.

Apply results to noise cancellation approaches.

Gain of Esophageal Stethoscope

Gain(dB)

Frequency (Hz)

Step 2: Test Recordings

In OR: 30-second recordings of normal and abnormal heart and lung sounds.

Adjust LabVIEWTM program settings to reduce ambient room noise.

Analysis and verification of recordings using MATLABTM programming environment.

Recording Setup

Laptop computer

External sound card

Two miniature condenser microphones in plastic housing

Dual channel preamp with 29dB gain

Step 1: Programming

LabVIEWTM graphical programming environment. Records esophageal stethoscope sounds as

stereo .wav files. Processes recordings to remove noise.