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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.
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).
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]
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.
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.
Artist's depiction of a foetus at 38 weeks' gestation. Foetal cerebral redistribution or 'brain-sparing' is a diagnosis in foetal medicine.It is characterised by preferential flow of blood towards the brain at the expense of the other vital organs, and it occurs as a haemodynamic adaptation in foetuses which have placental insufficiency.
Applying spectral Doppler to the renal artery and selected interlobular arteries, peak systolic velocities, resistive index, and acceleration curves can be estimated (Figure 4) (e.g., peak systolic velocity of the renal artery above 180 cm/s is a predictor of renal artery stenosis of more than 60%, and a resistive index, which is a calculated ...