Pulmonary Arterial Compliance Index (PACi) Calculator

Pulmonary Arterial Compliance Index (PACi): Explanation and Clinical Context Pulmonary arterial compliance reflects the pulsatile component of right ventricular afterload, calculated as stroke volume divided by pulmonary arterial pulse pressure (sPAP − dPAP). Indexing to body surface area yields the Pulmonary Arterial Compliance Index (PACi): SVI/(sPAP − dPAP), expressed in mL·m-2 per mmHg. Compliance represents the distensibility and buffering capacity of the pulmonary arterial system.

It declines early in pulmonary vascular disease, often before significant elevations in pulmonary vascular resistance (PVR), owing to the inverse hyperbolic relationship between PVR and PAC. Typical PAC in healthy adults ranges around several mL/mmHg, whereas values < 1 mL/mmHg are common in pulmonary arterial hypertension (PAH). Reduced PAC is associated with impaired right ventricular-arterial coupling and worse prognosis.

When stroke volume is unavailable, it can be estimated from cardiac output and heart rate (SV = CO × 1000 / HR). PACi normalizes compliance for body size, improving longitudinal follow-up and prognostic assessment in PH.