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The arterial resistivity index (also called as Resistance index, abbreviated as RI), developed by Léandre Pourcelot , is a measure of pulsatile blood flow that reflects the resistance to blood flow caused by microvascular bed distal to the site of measurement.
One parameter to quantify this difference is the pulsatility index (PI), which is equal to the difference between the peak systolic velocity and the minimum diastolic velocity divided by the mean velocity during the cardiac cycle. This value decreases with distance from the heart.
In fluid dynamics, a flow with periodic variations is known as pulsatile flow, or as Womersley flow.The flow profiles was first derived by John R. Womersley (1907–1958) in his work with blood flow in arteries. [1]
Pulse pressure is calculated as the difference between the systolic blood pressure and the diastolic blood pressure. [3] [4]The systemic pulse pressure is approximately proportional to stroke volume, or the amount of blood ejected from the left ventricle during systole (pump action) and inversely proportional to the compliance (similar to elasticity) of the aorta.
An increased pulsatility may be caused by cirrhosis, as well as increased right atrial pressure (which in turn may be caused by right heart failure or tricuspid regurgitation). [9] Portal vein pulsatility can be quantified by pulsatility indices (PI), where an index above a certain cutoff indicates pathology:
It is measured by dividing the pulsatility index of the middle cerebral artery of the foetus by the pulsatility index of the umbilical artery of the foetus. A cerebroplacental ratio lower than 1-1.1 in uncomplicated pregnancies is indicative of placental insufficiency, independent of the actual fetal size.
This page was last edited on 8 December 2023, at 14:57 (UTC).; Text is available under the Creative Commons Attribution-ShareAlike 4.0 License; additional terms may apply.
After Shigeo Satomura who detected for the first time the blood flow with a Doppler Ultrasound machine, [1] Gene Strandness measured the blood pressure at the ankle (1967), Léandre Pourcelot proposed the Arterial resistivity index (1974), and Gosling the Pulsatility index (1974).