Pulmonary Vascular Capacitance is Associated with Vasoreactivity and Long-Term Response to Calcium Channel Blockers in Idiopathic Pulmonary Arterial Hypertension

This study aimed to identify the relationship between pulmonary vascular capacitance (PVC) and vasoreactivity in patients with idiopathic pulmonary arterial hypertension (IPAH), and the value of PVC in predicting long-term response to CCB treatment. Pulmonary vasodilator testing with inhaling iloprost was performed in 308 newly diagnosed IPAH patients. Acute vasodilator-responsive patients accepted CCBs treatment. Patients who benefit from long-term CCB were defined as those being in World Health Organization (WHO) functional class II or I after at least 1 year on CCB monotherapy. PVC had significant correlations with WHO function class, 6-min walk distance, mean pulmonary arterial pressure, and pulmonary vascular resistance (r = -0.363, p < 0.001; r = 0.333, p < 0.001; r = -0.514, p < 0.001; r = -0.739, p < 0.001). Thirty-five acute vasodilator-responsive IPAH patients (11.4 %) displayed less severe disease and a higher baseline PVC (1.5 +/- 0.6 vs. 1.1 +/- 0.7 ml/mmHg, p = 0.003). During acute vasodilator testing, PVC increased significantly by mean of 79 +/- 48 % and reached to a higher absolute value of 2.6 +/- 1.5 ml/mmHg compared with non-responsive patients (1.4 +/- 1.5 ml/mmHg, p < 0.001). Furthermore, PVC increased more during acute vasodilator testing in the 24 patients who benefit from long-term CCB treatment (1.4 +/- 1.3 vs. 0.5 +/- 0.4 ml/mmHg, p = 0.004). The OR of increased PVC during vasodilator testing for predicting patients with long-term response to CCB was 1.24 (95 % CI 1.02-1.50, p = 0.031) as assessed by multivariable logistic regression analysis. PVC was higher in acute vasodilator-responsive IPAH patients and may be a predictor of long-term response to CCBs therapy.