Calculate the Doppler resistive index, RI = (PSV − EDV) / PSV, from peak systolic and end-diastolic velocity, or average up to three waveforms.
Measurement disclaimer: When averaging, use technically acceptable waveform pairs from the same named vessel, segment, side, and protocol. This descriptive summary is not a diagnosis or treatment recommendation.
Repeated-Waveform Resistive Index Formula
This calculator applies the Pourcelot resistive index formula to one Doppler waveform, or separately to two or three waveforms, then reports the arithmetic mean, range, and sample standard deviation of those RI values.
- PSV is peak systolic velocity.
- EDV is end-diastolic velocity.
- RI is unitless because both velocities use the same unit.
- s is the descriptive sample standard deviation of the three entered RI values.
Measurement Requirements
To average repeated measurements, use technically acceptable waveforms from the same named vessel, segment, side, patient state, and acquisition protocol. Do not average values from different organs, vessels, sides, or examination settings. Select the actual unit for each PSV and EDV. The calculator converts velocities before taking each ratio.
The range and sample standard deviation show how these three entered values differ. They do not quantify all measurement uncertainty and do not establish whether a result is normal or abnormal.
Interpretation Limits
Resistive index depends on the vascular bed, organ, hemodynamics, age, patient condition, waveform sampling, and equipment technique. There is no single universal RI cutoff that can diagnose stenosis, rejection, fibrosis, or another condition across all applications. A qualified clinician or sonographer should interpret the original waveforms and the protocol-specific context.
Frequently Asked Questions
Can I enter just one waveform?
Yes. One PSV and EDV pair gives the RI. Add a second or third waveform from the same vessel to get their mean, range and sample standard deviation.
Can EDV be negative?
Negative EDV can occur with reversed diastolic flow and may produce RI above 1. The clinical meaning depends on the vessel and waveform context.
Is the sample standard deviation a diagnostic result?
No. It is only a descriptive statistic for the three RI values entered here.
