Evaluation of Artificial Valves as an Orifice Model

Abstract

Artificial valves have been successfully transplanted in valvular heart diseases by open heart surgery. The characteristics of artificial valves as stenosis was studied from view point of fluid dynamics. 23 papers published from 1966-1980 were studied which described the relationship between pressure loss and flow across the valve in in vitro experiments. The pressure loss (ΔP) and the flow across the valve was obtained from the pressure-flow curve in figures or in the tables from these papers. The velocity was calculated from flow and external diameter (D) of the valve. Pressure loss coefficient λ was calculated using the following equation. λ=ΔP/1/2ρU²where Δ² P is the pressure drop (dyn/cm²), ρ is fluid density (g/cm³) and U is the flow velocity (cm/sec). Pressure loss and velocity was obtained from 3 different points at the same curve.
The shape of artificial valve was assumed to be like an orifice in a pipe. The relationship between the pressure loss coefficient λ and the cross-sectional area ratio (total occlusion, 100%) are commonly known for the orifice.
Cross-sectional area ratio of artificial valve was derived from pressure loss coefficient λ. The average value of crosssectional area ratio of stenosis was 58 (54-64)% in artificial valves. The value in xenograft (Hancock) valve was 63% and was not so small in comparison with other mechanical valves.