In Vitro Comparison of Observed and Calculated Mitral Valve Areas

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Abstract
Mitral valve bioprostheses (29 mm in diameter) were tested to determine how well areas observed in vitro correlated with the areas calculated using clinical formulas. A hydromechanical left heart and a mock circulation provided close simulation of physiological geometxies, pressures and flows. The test facility was instrumented to accurately measure and record unsteady pressure and flow. Transparent materials allowed detailed cinematography of valve action from the ventricular aspect. The photographic records were digitized and computer processed to determine the temporal variation of valve area at three different heart rates. The calculated valve areas were obtained by substituting pressure and flow measurements into the formulas of Aaslid and Gorlin and compared with the maximum observed areas measured at the exit plane of the valves. The Aaslid formula uses the instantaneous transvalvular pressure difference measured at peak flow. The Gorlin formula uses mean transvalvular pressure difference and stroke volume during ventricular diastole. The observed and calculated areas correlated well for the three Hancock (Hancock Laboratories, Inc., Anaheim, California, U.S.A.) and two Carpentier‐Edwards (Edwards Laboratories, Santa Ana, California, U.S.A.) valves tested, with the Aaslid formula showing a closer correlation than the Gorlin formula. The formulas, however, significantly underestimated the area calculated for the two Ionescu‐Shiley (Shiley, Inc., Irvine, California, U.S.A.) valves tested. The reasons for this discrepancy are discussed.