Pulmonary Artery Pressures

Measuring the pulmonary artery systolic pressures (PASP) is important in right heart disease. Two basic measurements are needed, and the data is then input into a formula that helps calculate PASP.

Measure peak tricuspid valve gradient -

Calculate velocity (v) across the tricuspid valve. The peak gradient is calculated using the modified Bernoulli equation

Peak gradient = 4 x v2

Measure right atrial pressure (RAP) -

This is done by measuring the diameter of the inferior vena cava on subcostal view, and the degree of collapse on inspiration. The value obtained is an estimate given that the degree of collapse estimated is subjective.

Diameter of IVC on expiration (cm)	IVC collapse on inspiration (%)	Estimated right atrial pressure mmHg
< 2	Full collapse	0 - 5
< 2	> 50	5 - 10
> 2	25 - 50	10 - 15
> 2	< 25	15 - 20

Pulmonary artery systolic pressure = Peak gradient + RAP

Pulmonary hypertension is defined as a elevated PASP > 25 mmHg at rest or > 30 mmHg on exercise.