How does aortic valve orifice area change with flow in normal versus stenotic human aortic valves?
In vitro assessment demonstrates that stenotic aortic valves do not increase their maximal orifice area beyond flow rates of 3 L/min, suggesting that the Gorlin equation may overestimate anatomic orifice area in patients with severe stenosis and high cardiac output.
The ability to measure aortic valve area clinically has emphasized the need to understand the changes in aortic valve orifice area during flow. To compare the performance of normal and stenotic human aortic valves we used a pulsatile flow model that simulated in vivo flow conditions. Five normal autopsy specimens and 15 stenotic valves removed at operation were mounted into the model. Valve function was assessed by analysis of video recordings of valve leaflet motion during flow. Over the flow rates tested normal valves demonstrated a linear increase in orifice area. There was no resistance to leaflet opening and valve closure was rapid. The majority of stenotic valves demonstrated an increase in orifice area at low flow rates. No valve showed any increase in maximal area beyond flow rates of 3 l min-1. Increased leaflet resistance of these abnormal valves resulted in notably slower opening and closing rates. In patients with a high cardiac output and severe stenosis, overestimation of the anatomic orifice area derived by the Gorlin equation can result. This is not related to variability in maximal orifice area.
Montarello et al. (1990) studied this question.