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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.
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.
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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laser Doppler imaging of pulse waves on the surface of the hand by holographic photoplethysmography from on-axis digital interferometry. Principal component analysis of digital holograms [23] reconstructed from digitized interferograms acquired at rates beyond ~1000 frames per second reveals surface waves on the hand. This method is an ...
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 ...
Velocity Time Integral is a clinical Doppler ultrasound measurement of blood flow, equivalent to the area under the velocity time curve. The product of VTI (cm/stroke) and the cross sectional area of a valve (cm2) yields a stroke volume (cm3/stroke), which can be used to calculate cardiac output.