Search

Heart sounds, the acoustic vibrations produced by the mechanical processes of the cardiac cycle, are modulated by respiratory activity. We have used computational techniques of cluster analysis and classification to study the effects of the respiratory phase and the respiratory resistive load on the temporal and morphological properties of the first (S1) and second heart sounds (S2), acquired from 12 healthy volunteers. Heart sounds exhibited strong morphological variability during normal respiration and nearly no variability during apnea. The variability was shown to be periodic, with its estimated period in good agreement with the measured split morphology was observed for S1 and S2 during inspiration. At high-breathing load, these changes became more prominent and occurred earlier in the respiratory cycle. Unsupervised cluster analysis was able to automatically identify the distinct morphologies associated with different respiratory phases and load. Classification of the respiration phase (inspiration or expiration) from the morphology of S1 achieved an average accuracy of 87 [+ or -] 7%, and classification of the breathing load was accurate in 82 [+ or -] 7%. These results suggest that quantitative heart sound analysis can shed light on the relation between respiration and cardiovascular mechanics and may be applied to continuous cardiopulmonary monitoring. phonocardiography; cardiopulmonary interaction; cluster analysis; classification; noninvasive monitoring

We evaluated the acoustic frequency response of endotracheal tubes (ETs) to assess their effect on respiratory system sound transmission studies. White noise 150-3300 Hz was introduced into 4.0-, 6.0-, and 8.0-mm ETs and recorded at their proximal and distal ends. Four tubes of each size were studied at their original and normalized lengths, in straight and bent configurations, and at circuit pressures from 0 to 20 cm[H.sub.2]O. The characteristics of the sound transmission were compared using an analysis of variance for repeated measures. The average transmission amplitude varied directly with tube diameter. The position of peaks and troughs on the amplitude frequency distribution depended on tube length but not on tube diameter. The angle of the phase-frequency plot correlated well with the length of the tube and was independent of its diameter. A 90[degrees] bend in the tube had no effect on its sound transmission. Increasing the circuit pressure above ambient modified the frequency response only if volume changes occurred in the test lung. When used to conduct sound into the respiratory system an ET affects the incident signal predictably depending on its length and diameter but not on its curvature or circuit pressure. Index Terms--Pulmonary acoustics, respiratory sounds, sound transmission.