Measurement of Carotid Bifurcation Pressure Gradients Using the Bernoulli Principle

Abstract

Current randomized prospective studies suggest that the degree of carotid stenosis is a critical element in deciding whether surgical or medical treatment is appropriate. Of potential interest is the actual pressure drop caused by the blockage, but no direct non-invasive means of quantifying the hemodynamic consequences of carotid artery stenoses currently exists. The present prospective study examined whether preoperative pulsed-Doppler duplex ultrasonographic velocity (v) measurements could be used to predict pressure gradients (ΔP) caused by carotid artery stenoses, and whether such measurements could be used to predict angiographic per cent diameter reduction. Preoperative Doppler velocity and intraoperative direct pressure measurements were obtained, and per cent diameter angiographic stenosis measured in 76 consecutive patients who underwent 77 elective carotid endarterectomies. Using the Bernoulli principle (ΔP = 4v ²), pressure gradients across the stenoses were calculated. The predicted ΔP, as well as absolute velocities and internal carotid/common carotid velocity ratios were compared with the actual ΔP measured intraoperatively and with preoperative angiography and oculopneumoplethysmography (OPG) results. An end-diastolic velocity of ⩾ 1 m/s and an end-diastolic internal carotid artery/common carotid artery velocity ratio of ⩾ 10 predicted a 50% diameter angiographic stenosis with 100% specificity. Although statistical significance was reached, preoperative pressure gradients derived from the Bernoulli equation could not predict actual individual intraoperative pressure gradients with enough accuracy to allow decision making on an individual basis. Velocity measurements were as specific and more sensitive than OPG results. ΔP as predicted by the Bernoulli equation is not sufficiently accurate at the carotid bifurcation to be useful for clinical decision making on an individual basis. However, end-diastolic velocities alone as well as internal carotid artery/common carotid artery velocity ratios are highly specific in the prediction of clinically significant carotid stenoses. An end-diastolic velocity of ⩾ 1 m/s accurately identifies a 50% or greater diameter stenosis, and thus may in some cases be sufficient for operation.