Spectral analysis and acoustic transmission of mitral and aortic valve closure sounds in dogs. Part 4: Effect of modulating cardiac inotropy.

A surgical protocol was designed to implant in dogs a programmable atrioventricular pacemaker and to destroy the bundle of His with one to four 0.1 ml formaldehyde injections. The heart rate and P-R interval were paced at 100 beats min-1 and 75 ms, respectively. Cardiac inotropy was then varied in five animals by using injections or infusions of cardiotonic drugs (Dobutamine, Betalol and Quinidine). Their effect on the spectra and acoustic transmission of the mitral M1 and aortic A2 closure sound components produced within the left heart and transmitted up to the body surface was studied. Results indicate that changes in cardiac inotropy strongly modify the intensity of M1 and A2 but do not markedly affect their spectral distribution. They also affect the transfer function of the heart/thorax acoustic system, but this influence is small compared with that of a 12 min reference interval. In addition, it was shown that the intensity of M1 is more sensitive to the cardiotonic agents than the intensity of A2.