In seven patients with idiopathic or secondary pulmonary arterial hypertension (PAH), ventilation-perfusion (V (A)/Q ) relationships were measured during a right heart catheterization using the multiple inert-gas elimination technique before and during intravenous infusion with epoprostenol (EPO), and following 5 months of 20 microg inhaled iloprost taken three times daily (ILO). Pre-treatment pulmonary vascular resistance (PVR) was 9.3+/-5.0 mmHg/l/min and the dispersion of perfusion and ventilation for V (A)/Q -ratios was increased. EPO reduced PVR by 20%, and increased cardiac output, shunt, and mixed venous oxygenation (SV(O2)). The arterial oxygen tension (Pa(O2)) remained unchanged. Basal central haemodynamics did not change after 5 months of ILO. Fifteen minutes after ILO, PVR decreased by 20%, and the shunt, SV(O2), and Pa(O2) remained unaltered.
Conclusions: In secondary PAH with normal lung volumes, significant V (A)/Q mismatching occurred. The PVR was reduced to a similar degree during EPO and after ILO, but only EPO increased the shunt and SV(O2). EPO and ILO did not significantly affect the Pa(O2).