Modification of the Gorlin equation for use with heart valve substitutes

The Gorlin equation, which was used to assess the obstruction to flow by a stenosed heart valve, is based on steady flow (time independent) criteria derived from hydraulics. Recently, this equation has been used to obtain an effective orifice area for heart valve substitutes both in vitro and in vivo. In this study, a modification of the original Gorlin equation for use with heart valve substitutes considers both the pulsatility of the valvar flow and possible variations in volumetric flow waveforms induced by differences in myocardial performance. The modified equation also allows for the possibility of regurgitant flows. Its use is illustrated in a study of the hydrodynamic performance of a series of heart valve substitutes and recommendations are made concerning its application to cardiac catheterisation procedures.