MEASUREMENT OF RESPIRATORY ACOUSTICAL SIGNALS - COMPARISON OF SENSORS

We assessed the performance of three air-coupled and four contact sens ors under standardized conditions of lung sound recording. Recordings were obtained from three of the investigators at the best site on the posterior lower chest as determined by auscultation. Lung sounds were band-pass filtered between 100 and 2,000 Hz and sampled simultaneously with calibrated airflow at a rate of 10 kHz. Fourier techniques were used for power spectral analysis. Average spectra for inspiratory soun ds at flows of 2 +/- 0.5 L/s were referenced against background noise at zero flow. Air-coupled and contact sensors had comparable maximum s ignal-to-noise ratios and gave similar values for most spectral parame ters. Unexpectedly, less sensitivity (lower signal-to-noise ratio) at high frequencies was observed in the air-coupled devices. Sensor perfo rmance needs to be characterized in studies of lung sounds. We suggest that lung sound spectra should be averaged at known over several brea ths and that all measurements should be reported relative to sounds re corded at zero flow.