In vitro study of the pressure-velocity relation across stenotic orifices

In a hand-driven, pulsatile in vitro model, the pressure-velocity relation across stenotic orifices was studied from simultaneous measurements recorded over a wide range of pressure and across different-sized orifices, individually and paired. Velocity spectra were recorded with continuous-wave Doppler ultrasound. In a rigid, noncompliant system, integrated instantaneous maximal velocities precisely register simultaneous integrated pressure gradients without measureable phase shift. Across stenotic orifices of 5 to 10 mm in diameter, the pressure-velocity relation is independent of orifice size for pressures extending from -30 to +240 mm Hg. The relation is quadratic and crosses 0. In this model, application of the simplified Bernoulli equation transforms the relation from curvilinear to linear with a bias toward the derived-pressure axis. In the presence of 2 different-sized orifices, the pressure-velocity relation remains constant, with a given pressure producing 2 identical velocities.