The Venturi Effect and Cerebrovascular Ultrasound

Abstract

Background: One of the most frequent diagnostic pitfalls in cerebrovascular ultrasound is the evaluation of the vertebrobasilar system in the case of vertebral artery (VA) hypoplasia because the diagnostic findings are sometimes suggestive of significant pathologies, but may be completely normal as well. The Venturi effect is a phenomenon of hydrodynamics which describes a drop in hydrostatic pressure along areas of high flow velocities. Method: We review the physical background of the Venturi effect and describe how it can explain both physiological and pathological flow phenomena encountered during cerebrovascular ultrasound investigations. We focused on flow phenomena at the vertebrobasilar junction by theoretically calculating conditions with different influx angles and flow velocities on two-dimensional digital subtraction angiography images. In the discussion, we also address other areas of cerebrovascular ultrasound, where the Venturi effect is of particular interest. Results and Conclusions: The blood flow velocity within the VAs and the angle between a hypoplastic VA and the basilar artery (BA) are important determinants of the intraluminal pressures of these arteries and thus their resistances. In the case of angles below 90° between the distal VA and the BA, abnormal extracranial flow profiles may suggest downstream VA stenosis or occlusion, whereas in the case of angles above 90°, a diagnosis of an AV fistula downstream to the V4 segment may be assumed. Furthermore, various hemodynamic effects at the site of a stenosis of the brain supplying arteries can also be explained by a transstenotic pressure drop created by the Venturi effect, particularly the generation of musical murmurs. The systolic dip (‘systolic deceleration’) at the origin of the VA due to subclavian artery stenosis is also a consequence of the Venturi effect.

Effect of hemodialysis access blood flow on cardiac events after coronary artery bypass grafting using an internal thoracic artery

“…This may be explained by decreased peripheral resistance in the heart vasculature during diastolic relaxation, protecting myocardium from steal (18). High blood flow velocity in HD AVF may cause a Venturi effect, a phenomenon of hydrodynamics that describes a drop in hydrostatic pressure along areas of high flow speed (19), potentially creating a suction effect of subclavian artery on ITA. Such a phenomenon is more prominent during systole, leading to an appearance of a systolic dip (�systolic deceleration�) described in cerebrovascular circulation (19).…”

“…High blood flow velocity in HD AVF may cause a Venturi effect, a phenomenon of hydrodynamics that describes a drop in hydrostatic pressure along areas of high flow speed (19), potentially creating a suction effect of subclavian artery on ITA. Such a phenomenon is more prominent during systole, leading to an appearance of a systolic dip (“systolic deceleration”) described in cerebrovascular circulation (19). The unique characteristic of myocardial perfusion, mainly occurring during diastole, may lead to diminishing the impact of Venturi effect on the ITA CABG blood flow.…”

Effect of Arteriovenous Hemodialysis Shunt Location on Cardiac Events in Patients Having Coronary Artery Bypass Graft Using an Internal Thoracic Artery

“…The difference between these two anastomoses is that AV HD fistula represents a low‐resistance vascular bed, while ITA‐coronary anastomosis is characterized by a relatively high vascular resistance. High blood flow velocity in HD fistula may involve a Venturi effect, a phenomenon of hydrodynamics that describes a drop in hydrostatic pressure along areas of high flow speed . Development of such a phenomenon in the subclavian artery may create a suction effect on all the branches of this vessel, and so, may result in a reversed flow in ITA ipsilateral to AV shunt, stealing blood away from coronary circulation .…”

Safe Introduction and Quality Control of New Methods in Coronary Surgery

“…The importance of such emboli during heart surgery has been documented (118). The increased number of gaseous emboli in the Symmetry R group was surprising, but may have been due to a Venturi effect occurring while punching the hole in the aorta before the application of the connector (119). …”