Diagnostic Performance of Pulmonary Capacitance at Rest and During Exercise in Idiopathic Pulmonary Arterial...

Reliable markers of early disease are needed in pulmonary arterial hypertension (PAH). As measures of the contribution of abnormal vascular compliance to overall vascular resistance, resting and exercise pulmonary capacitance-defined as the stroke volume divided by the change in pulmonary pulse pressure-may be sensitive markers of early disease.

We examined all patients in our pulmonary hypertension database with idiopathic PAH, who had undergone rest and exercise right heart catheterisation in one sitting. Standard haemodynamic measurements were obtained, including pulmonary capacitance. These results were compared to age- and sex-matched normal controls.

We analysed 27 right heart catheterisations in idiopathic PAH patients and 23 in controls. Mean pulmonary artery pressure (MPAP), mean pulmonary capillary wedge pressure (mPCWP), pulmonary vascular resistance (PVR) and right ventricular stroke work index (RVSWI) were significantly higher at baseline in diseased patients, while Cardiac Index (CI) and pulmonary capacitance were significantly lower. MPAP, mPCWP, cardiac index and RVSWI increased significantly in both groups with exercise. Pulmonary capacitance decreased significantly in both groups. Pulmonary vascular resistance decreased with exercise in the control group only. Capacitance and PVR were inversely correlated at rest (time-constant of 0.79s) and with exercise (time-constant of 0.56s). The receiver operating characteristic (ROC) curve for capacitance as a diagnostic marker demonstrated an AUC of 0.96 at rest and 0.95 with exercise.

In idiopathic pulmonary arterial hypertension (IPAH) there is a reduction in pulmonary capacitance at baseline and left-shift of the inverse capacitance-PVR relationship with exercise. Both resting and exercise pulmonary capacitance have potential as diagnostic markers in early disease.