Relationship of aortic regurgitant velocity slope and pressure half-time to severity of aortic regurgitation under changing haemodynamic conditions

The slope and pressure half-time of the aortic regurgitant velocityspectrum have been used as non-invasive markers of regurgitantseverity. Recent in vitro and theoretical work, however, hassuggested a confounding effect of systemic vascular resistanceand left ventricular compliance on these parameters. To studythis situation in vivo, we have investigated the determinantsof the aortic regurgitant velocity profile in an animal modelof aortic regurgitation in which the regurgitation was inducedsurgically and in which the afterload was varied pharmacologically.Specifically, we examined the relationship of slope and pressurehalf-time of the aortic regurgitant velocity profile to theseverity of aortic regurgitation under varying conditions ofafterload using multilinear analysis. Slope varied directlywith regurgitant orifice area and inversely with systemic vascularresistance and both left ventricular and aortic compliance (allP<0.001). Pressure half-time related to these variables inthe opposite direction. When the regurgitant orifice was variablein size, slope related directly (P<0.001) and half-time inverselyto the severity of the aortic regurgitation (the clinicallyexpected response). In contrast, when the regurgitant orificearea was constant, slope varied inversely (P<0.001) and half-timevaried directly (P<0.07) with the severity of the aorticregurgitation. Following nitroprusside infusion, slope tendedto increase (P=0.08) and pressure half-time tended to shorten(P=0.08) despite a significant reduction in the regurgitantfraction (P=0.009). Similarly, following dopamine infusion,a significant increase in regurgitant fraction (P=0.01) wasassociated with a slight fall in aortic regurgitation slopeand a lengthening of the half-time. The conventionally anticipated alterations in aortic regurgitationvelocity slope and pressure half-time predict the change inthe severity of aortic regurgitation when this is varied bychange in the size of regurgitant orifice but are unreliablewhen this is altered by pharmacological manipulation of theafterload.