pulsatility

Pulsatility is the rhythmic variation in a physical quantity—most commonly arterial blood flow or pressure—that corresponds to the heartbeat. In the systemic circulation, the heart's contraction produces alternating systolic increases and diastolic declines, yielding a pulsatile waveform shaped by arterial compliance, peripheral resistance, and wave reflections from the vascular tree. This pulsatile nature is evident in measurements of blood velocity, pressure, and sometimes tissue perfusion.

Quantification of pulsatility is often described using Doppler ultrasound indices such as the Pulsatility Index (PI) and the Resistive Index (RI). PI is calculated as (S - D)/M, where S is peak systolic velocity, D end-diastolic velocity, and M the mean velocity over a cardiac cycle. RI is (S - D)/S. These indices reflect the resistance and compliance of the downstream vasculature but must be interpreted in context, including heart rate and systemic conditions.

Clinical relevance includes the association between increased pulsatility and higher downstream resistance or reduced arterial compliance, seen with aging, hypertension, or atherosclerosis. Elevated pulsatility can occur in kidney diseases (e.g., renal artery stenosis) or in obstetric assessments such as fetal well-being via the umbilical artery. Very high pulsatility in cerebral or ocular vessels may indicate vascular pathology or intracranial pressure changes, while low or absent pulsatility can arise in low-flow states or severe distal obstruction.

Pulsatility is influenced by heart rate, blood pressure, and cardiac output, and it is a useful concept in studying arterial stiffness, wave reflections, and microvascular function across cardiology, nephrology, neurology, and obstetrics.