Direct Detection and Timing of Aortic Valve Closure.

• The aortic incisura and the second heart sound have been considered simultaneous with and caused by aortic valve closure for many years. While Wiggers believed in a noiseless approximation of the semilunar valves and that after-vibrations of the closed valves and aortic blood column caused the second sound, the incisura was related to semilunar valve closure. Thus, subsequent studies relating the second heart sound to the incisura associated the sound with closing of the valve.~' However, the possibility of an earlier closure of the valve has been suggested by recent cineangiocardiographic studies, by ventricular-aortic pressure gradient reversal prior to the incisura, and by the presence of backflow in the aorta several milliseconds before the incisura." In order to clarify this, a means of directly detecting aortic valve closure seemed necessary. Additional requirements were that normal valve movements and vascular pressures and functions be maintained. Toward this end, an electrical contacting device and techniques for its insertion between the leaflets of the aortic valve in closed chest, anesthetized dogs were developed.