Pulmonary arterial compliance & PAPi

Cpa, PAPi · Cpa = RV SV / (PASP − PADP); PAPi = (PASP − PADP) / RAP; PADP from the end-diastolic PR velocity + RAP

Normal range & thresholds

• Cpa <2.3 mL/mmHg was associated with mortality in idiopathic PAH (invasive) ^[119].
• PAPi <0.9 predicted RV failure after inferior MI (invasive) ^[120].

Echo estimates of both are approximate.

Pathophysiology

Compliance is the pulsatile load of the pulmonary circulation; it falls early in pulmonary vascular disease, often before PVR rises much. PAPi relates pulse pressure the RV can generate to its filling pressure — a crude index of RV contractile reserve.

Raised by

• Healthy pulmonary vasculature (Cpa)

Lowered by

• PAH, CTEPH, left-heart PH (combined), RV infarction (PAPi)

Technique & pitfalls

• Needs clean TR and PR envelopes and an IVC-derived RAP; state all three inputs.

Pseudo-change & artefact

• Compounded Doppler errors; RAP estimate dominates PAPi.

Treatment thresholds

Validated invasively, not as echo decision thresholds; use as supportive information in PH and RV failure ^[8].

Next step

• Right-heart catheterisation when decisions depend on it.

Drugs

Pulmonary vasodilators improve Cpa in responders.

Reversibility

Partial with treatment.