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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.
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.
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 place of the stethoscope, a Doppler ultrasound beam measures the blood flow pulsations in intracranial and extracranial segments of the ophthalmic artery. The non-invasive ICP meter based on this method gradually increases the pressure over the eyeball and intraorbital tissues so that the blood flow pulsation parameters in two sections of ...
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.
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).
The optimal timing of delivery for a fetus with IUGR is unknown. However, the timing of delivery is currently based on the cause of IUGR [6] and parameters collected from the umbilical artery doppler. Some of these include: pulsatility index, resistance index, and end-diastolic velocities, which are measurements of the fetal circulation. [26]
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