Validation of the orifice formula for estimating effective heart valve opening area

Abstract

Interest in the Gorlin formula for estimating heart valve effective orifice area (EOA) has recently been rekindled and the formula itself has been challenged. In this validation study, explanted native heart valves, unimplanted mechanical prostheses, unimplanted bioprostheses and explanted bioprostheses have been tested in vitro in a pulsatile flow simulator. Pressures have been measured 30 mm upstream and 100 mm downstream from the plane of the valve sewing ring (to give pressure drop, pd in kPa). Flow (Q in 1 min-1) has been measured directly by electromagnetic flowmeter and orifice areas have either been taken from manufacturer supplied data (mechanical valves) or have been digitised from video images at maximum orifice (biological valves). The formula EOA = Q/(6.96 x pd 1/2) - 0.7 fitted the data with good correlation, r = 0.96 (n = 179). The orifice assumption on which this formula is based (cf. Gorlin formula) is confirmed though it is recommended that the formula should be modified to account for (i) the pressure recovery phenomenon and (ii) the fact that forward flow through a valve only occurs over a portion of the cycle in pulsatile flow. Heart rates used in the study ranged from 40 to 140 min-1, stroke volumes ranged from 20 to 114.3 ml, cardiac outputs from 2.0 to 8.0 1 min-1 and peripheral resistance from 0.1 to 1.6 kPa 1-1 min (1 - 12 mmHg l-1 min). Application of the formula was independent of the flow conditions.

Flow Visualization of Three-Dimensionality Inside the 12 cc Penn State Pulsatile Pediatric Ventricular Assist Device

“…For these studies two separate sets of valves were used. One pump contained 17 mm Bjork-Shiley Monostrut (BSM) valves, which have an effective orifice area (EOA) of 1.1 cm 2 , and the other, 16 mm CarboMedics (CM) bi-leaflet valves, with an EOA of 1.06 cm 2 7 The BSM valves were oriented so that the major orifice opened to the outside wall of the device and the strut was parallel to the diaphragm. The CM valves were oriented so the B-datum line, which separates the two leaflets, was perpendicular to the diaphragm.…”

Flow Behavior Within the 12‐cc Penn State Pulsatile Pediatric Ventricular Assist Device: An Experimental Study of the Initial Design

“…For the 50-cc device, we typically use a 21-mm BSM valve with an EOA of 2.0 cm 2 (20). For the 17-mm BSM valves used in the 12-cc device, the EOA is 1.1 cm 2 .…”