Pulmonary Artery Systolic Pressure (sPAP)

Systolic pulmonary artery pressure (sPAP) is a hemodynamically important parameter that is routinely assessed during echocardiography. Estimation of sPAP is based primarily on the pressure gradient across the tricuspid valve, calculated from the peak tricuspid regurgitation velocity using continuous-wave Doppler. This measurement alone often provides a good qualitative assessment of whether pulmonary artery pressure is normal or elevated. A more accurate quantitative estimate is obtained by adding the estimated central venous pressure (CVP), derived from the diameter and respiratory variation of the inferior vena cava. The physiology underlying this method is straightforward and can be understood using the concept of two communicating vessels.

Upper Communicating Vessel

During systole, the pulmonary valve is open. The right ventricle (RV) and pulmonary arteries (PA) therefore form a communicating vessel, meaning that the pressure is essentially the same throughout the system from the right ventricle to the pulmonary arteries.

Lower Communicating Vessel

The right atrium and inferior vena cava likewise form a communicating vessel. Consequently, right atrial pressure can be estimated from the central venous pressure (CVP).

Estimating Pulmonary Artery Systolic Pressure

Adding the estimated central venous pressure (CVP) to the RV/RA pressure gradient provides an estimate of the pulmonary artery systolic pressure (sPAP):

sPAP ≈ CVP + RV/RA pressure gradient

CVP is estimated from the diameter of the inferior vena cava (IVC) and its respiratory variation, whereas the RV/RA pressure gradient is calculated from the peak velocity of the tricuspid regurgitation jet. Both measurements are described in the following sections.

In practice, measuring the tricuspid regurgitation gradient from several echocardiographic views provides a qualitative estimate of whether pulmonary pressure is elevated. As a practical rule of thumb, a tricuspid regurgitation gradient of approximately 25 mmHg can be used as a threshold for elevated pulmonary pressure.