Methods: Five polymeric trileaflet valves (annulus diameter = 25 mm) with varying leaflet stiffness (Young's moduli of 0.90 to 5.24 MPa) were fabricated to simulate valve degeneration and tested in the aortic position of a pulse-duplicator. Cardiac output (CO), LV dp/dt, aortic input resistance and compliance were independently varied to create different hemodynamic states for each valve. Pressure drops were measured across the valve used to calculate EOA (Gorlin equation) and R. Aortic pressure was measured 3 cm (p1) and 10 cm (p2) distal the valve annulus to simulate Doppler and catheterization measurements. Anatomic areas (AOA) were recorded by high speed photography. The relative effects of valve stiffness, LV dp/dt, aortic compliance and input resistance on EOA, AOA, and R were determined using a forward linear regression model.

Results: Under similar hemodynamic conditions, EOA ranged from 0.68 to 0.95 cm2. AOA (1.4-1.8 cm2) highly correlated with EOA (p<0.001); both demonstrated flow dependence. EOA varied more with CO than R (24.3±4 % vs. 4.7±1.9 %) (Fig 2). The extent of valve opening and hence the AOA showed flow dependence (Fig. 1). EOA correlated with valve stiffness, LV dp/dt, arterial resistance and compliance, with valve stiffness accounting for 65% (r2=0.65) of the variance in EOA, while arterial compliance, input resistance, and LV contractility explained the remainder (all p<0.001). On the other hand, valve stiffness explained 98% variance in R (r2= 0.98) (p<0.001). Based on model parameters, the following equation was determined to evaluate valve stiffness based on valve resistance valve stiffness (psi) = 5.3*Valve resistance (dyne s/cm5) - 0.006

Conclusions: Valve resistance better reflects the degree of valve degeneration and is less affected by changes in hemodynamic conditions. Aortic impedance has a greater influence on EOA than on R. This has implications in the assessment of aortic stenosis in patients with coexisting hypertension or LV dysfunction.