Valve dynamics.

Flow between two contiguous elastic sheets (valve leaflets) generates one of two types of behavior. At low pressure differences, e.g. 1 cm H2O, the sheets part slightly and the fluid passes silently between them. The aperture under these silent conditions varies with the square of the length of the orifice, the transvalvular pressure difference and the kinetic energy, divided by the thickness of the leaflets. At higher transvalvular pressure differences the downstream end of the bicuspid valve alternately closes and reopens (flitter), and functions as an acoustic oscillator. The recurrence rate of flitter varies with the tension on the leaflets and inversely with the thickness. The threshold of the onset of flitter varies with the product of the pressure and the square of the length of the valve aperture, divided by the wall tension and thickness. The significance of these data in the onset of the flitter and of the recurrence rate is discussed in terms of the production of sounds and murmurs at the heart valves, vocal cords and other sites.