pulsatility index
Doppler ultrasound parameter measuring the variation between peak systolic and end-diastolic velocities relative to mean velocity in vascular studies.
Full Definition
The pulsatility index (PI) is a calculated Doppler parameter that reflects vascular resistance and compliance by measuring the difference between peak systolic and end-diastolic velocities divided by the time-averaged maximum velocity. This dimensionless index is particularly important in cerebrovascular, renal, and peripheral vascular imaging, where it helps assess downstream resistance and vascular health. Normal values vary by vessel and patient age, with elevated PI suggesting increased downstream resistance or reduced vessel compliance. Editors must distinguish PI from resistive index (RI) and understand that PI is less dependent on diastolic flow than RI, making it useful even when diastolic flow approaches zero. The parameter is critical in obstetric vascular assessments and transplant evaluations.
Usage
Usage note: Abbreviate as PI when context is clear; always spell out on first use in formal reports.
In Context
- "Elevated pulsatility index in the middle cerebral artery suggested increased intracranial pressure." — Transcranial Doppler report
- "The renal artery showed an abnormal pulsatility index of 1.8, indicating downstream pathology." — Renal Doppler study