A method for studying the effects of PR and RR intervals on heart sound power spectra

Abstract

Models of valve sound production [1][2] and cl inical studies [3][4][5][6][7][8] have demon strated that the natural modes of reso nance of biological heart valves increase with calcium deposit and stiffening of the valve leaflets.In the course of ex ploring the potential of spectral analy sis of valve closing sounds for the de tection of valvular degeneration, a method was developed for determining, in dog, the influence of PR interval (PRI) and heart rate (HR) on the spectra of intracardiac and thoracic first and sec ond heart sounds. METHOD AND ANALYSISA surgical protocol was designed to implant, in dogs, a Medtronic AV sequen tial rate-programmable pacemaker (Model 7005C) and to destroy the AV node with one to four 0.1 ml formaldehyde inj ec tions.After a recovery period of two to three weeks, a second investigation was then set-up to record the following sig nals: the ECG, the intracardiac left ven tricular and aortic pressures, the intra cardiac left ventricular and aortic phonocardiograms (PCGs), two thoracic PCGs and the left ventricular pressure derivative. The thoracic sounds were recorded with two Hewlett-Packard contact microphones (Model 21050A). The in tracardiac measurements were obtained with a Millar dual-micromanometer catheter (Model SPV 350) inserted into the left or right carotid artery and pushed toward the left ventricle until pressure tracings showed that the distal transducer was in the left ventricle and the proximal in the aorta. All PCGs were processed by third order high-pass fil ters (50 HZ). PRI and HR were then var ied independently by using a Medtronic pacemaker programmer (Model 9710) and the signals recorded on a 8-channel Fostex FM tape recorder. During playback, the recorded sig nals were digitized with 12-bit reso lution by using a Data Translation acqui sition board (Model DT-2801A) installedin an IBM-PC/ AT. A QRS detection algo ri thm was used to synchronize the cohe rent detection of the mitral and aortic valve closing sounds using a cross-corre lation technique. The individual sounds selected were corrected for their jitter and transformed in the frequency domain using a sine-cosine window and a fast Fourier transform algorithm.Estimates of the mitral and aortic closing sound power spectra were obtained by ensemble averaging over 50 cardiac cycles. RESULTS AND DISCUSSIONA typical example of the influence of PRI on the spectra of intracardiac and thoracic heart sounds is shown in Fig. 1. In this preliminary study done in one dog, four PRIs (25, 75, 125 and 175 msec.) were analyzed at a constant HR of 100 bpm. Panel A shows the results for 51 recorded within the left ventricle (S11v) and externally at the apex (Sl ao ) while panel B shows the results for 52 recorded within the aorta (52 �9 ) and ex ternally at the aortic area \62 ). It is clear that, for both intracar �ac and external recordings, the influence of the PRI is significant for Sl and relatively negligible for S2. Fig. 2 shows an example of the in fluence of HR on the spectra of the in tracardiac and thoracic S...