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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]
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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.
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:
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 the nervous system, pulsatility is observed in oscillatory activity from central pattern generators. In the heart, pacemakers are able to work and secrete in a pulsatile manner. A pulsatile secretion pattern is critical to the function of many hormones in order to maintain the delicate homeostatic balance necessary for essential life ...