Detection of pneumothorax visualized by computer analysis of bilateral respiratory sounds

Pneumothorax is usually diagnosed based on the attenuation of respiratory sounds of the affected side on auscultation, but it requires a skilled technique and is limited to subjective evaluation. Thus, we designed a device which analyzes and converts the frequency of auscultatory sounds to numerical values with a computer. With this device, the bilateral sound pressure levels were compared between groups of 25 healthy subjects and 21 patients with pneumothorax to investigate the efficacy of the diagnosing tool of pneumothorax. While recording respiratory sounds of the bilateral precordial regions, the fast Fourier transform was applied with a frequency analysis software, power spectra of the auscultatory sounds were displayed in real-time, and the sound pressure level was compared between the bilateral sides. The difference was investigated at frequencies judged as less likely to be influenced by cardiac sounds (200-400 Hz). No difference was observed in the control group (n = 25, P > 0.05), but respiratory sound attenuation was detectable on the affected side in the pneumothorax group (n = 21, P < 0.01 each for the paired Student's t-test and Wilcoxon signed-rank test). When the cutoff value was 8 dB, the sensitivity and specificity as diagnostic tool of pneumothorax was 71.4% and 100%, respectively. This device would facilitate the detection of occult pneumothorax at accident scenes, in emergency rooms and in intensive care units.