Doppler measurement of the pressure drop caused by arterial stenosis: an experimental study: a case report

A stenotic arterial lesion which reduces the cross-sectional area of the artery causes an increased velocity and, as a consequence, a loss in kinetic energy and a pressure drop. A simplified formula, derived from the Bernoulli principle, relates the pressure drop to the maximum velocity of the blood flow in the stenotic segment: delta P (mmHg) = 4 Vmax2 (m/sec). This formula has been validated for stenosis of cardiac valves. Aim of our study was to test the hypothesis that this formula applies in the major arteries using Doppler ultrasound with spectrum analysis. In our experiments we created artificial graded stenoses of varied geometry in the thoracic aorta of dogs. Invasive pressure measurements were obtained using intra-arterial needles on both sides of the stenosis. A Doppler signal was obtained with a 2.5 MHz CW probe, insonating the stenotic area from a distance, with an almost parallel approach. In these conditions the maximum Doppler frequency shift is an accurate estimate of the maximum flow velocity, according to the Doppler equation. We compared the Doppler derived (delta P = 0.36 Fmax2) and the invasive measurements of pressure drops. Our results show a highly significant correlation between the intra-arterial and the Doppler measurements of the pressure drops caused by arterial stenoses and encourage efforts in applying similar techniques in the noninvasive evaluation of vascular patients.