ASSESSMENT OF THE BJORK-SHILEY PROSTHETIC VALVE ORIFICE AREA IN THE AORTIC POSITION

The actual orifice area of a valve is still considered to be a valuabl e index for assessing prosthetic valve function. Valve orifice area as calculated by Gorlin's formula is, however, not constant but changes in proportion to the transvalvular flow rate. The purpose of the prese nt study was to examine the relationship between orifice area and flow rate across the Bjork-Shiley prosthetic valve as calculated by Gorlin 's formula, and to modify the formula in a series of patients with the Bjork-Shiley prosthetic valve in the aortic position. Fifty-six patie nts who had received aortic valve replacement with a Bjork-Shiley pros thetic valve underwent cardiac catheterization. Prosthetic valve orifi ce area was calculated by Gorlin's formula and then plotted against fl ow rate across the valve with respect to valve size. The relationship between orifice area and flow was linear. The discharge coefficient of Gorlin's formula was plotted against flow rate, and a linear correlat ion was obtained. By substituting Gorlin's formula for an empiric coef ficient into the function for transvalvular flow rate, a modified form ula that can predict the actual orifice area of the prosthetic valve i s obtained.