The formula to calculate the pulsatility index (PI) is:
\[ PI = \frac{Systolic \, V - Diastolic \, V}{Mean \, V} \]
Where:
The Pulsatility Index (PI) is a measure used in Doppler ultrasound studies to quantify the variability in blood flow velocity within a specific blood vessel. It is calculated by subtracting the diastolic velocity (the speed of blood flow when the heart is at rest) from the systolic velocity (the speed of blood flow when the heart is contracting), and then dividing the result by the mean velocity (the average speed of blood flow throughout the entire cardiac cycle). The PI provides information about the resistance to blood flow caused by changes in the blood vessel, such as narrowing or blockage. A higher PI indicates greater variability in blood flow velocity, which may suggest increased resistance or decreased compliance of the blood vessel. This can be indicative of various pathological conditions, such as vascular disease or fetal distress in obstetric applications.