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Resistive Index Formula:
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The Resistive Index (RI) is a Doppler ultrasound parameter that measures vascular resistance in arteries. It is calculated from peak systolic velocity (PSV) and end-diastolic velocity (EDV) measurements.
The calculator uses the Resistive Index formula:
Where:
Explanation: The RI quantifies the resistance to blood flow in a vessel, with higher values indicating greater resistance.
Details: RI is used in various clinical applications including renal artery stenosis evaluation, transplant kidney monitoring, and assessment of other organ perfusion. Normal values typically range from 0.5-0.7, but vary by organ and clinical context.
Tips: Enter PSV and EDV values in cm/s. PSV must be greater than EDV, and both values must be positive. The result is unitless and typically reported with two decimal places.
Q1: What is a normal Resistive Index range?
A: Normal RI values typically range between 0.5-0.7, but this can vary depending on the specific artery being measured and patient factors.
Q2: What does a high Resistive Index indicate?
A: Elevated RI values may indicate increased vascular resistance, which can be seen in conditions such as renal artery stenosis, renal parenchymal disease, or elevated intrarenal pressure.
Q3: Can RI be greater than 1?
A: Yes, RI can theoretically approach 1 when EDV is very low or reversed, which indicates extremely high vascular resistance.
Q4: What are the limitations of RI measurement?
A: RI can be affected by various factors including heart rate, vascular compliance, and technical aspects of Doppler measurement. It should be interpreted in clinical context.
Q5: How is RI used in renal transplant monitoring?
A: In transplant kidneys, rising RI values may indicate rejection, obstruction, or other complications, though it's not specific and requires correlation with other clinical findings.