Fig. 14.

Valve closure test. (a) Experimental traces showing changes in Pin, Pout and Psn pressures before, during and after closure of a normal valve in response to a Pout ramp (repeated twice). The vessel diameter does not return to its original level in the time period shown, due to the viscoelastic properties of the vessel wall. (b) Plot of ΔP at point of valve closure vs normalized vessel diameter for complete sets of valve closure tests on a normal (tight) valve, a valve with intermediate behavior, and a defective (leaky) valve, which never closed during the tests. The valve might close at higher Pout levels but the maximal Pout levels are kept under 40 cm H2O to prevent damage to the low-pressure transducers