Intravenous prostacyclin increased the cardiac index and raised the PVO2 and the PaO2 but again with no significant changes in Vd/Vt and Qs/Qt. Exercise produced an increase in cardiac index, a fall in PVO2, no significant change in PaO2 and also no appreciable changes in the Vd/Vt and Qs/Qt. The physiological shunt, Qs/Qt (15 +/- 17%) and the dead space, Vd/Vt (0.47 +/- 0.11) were elevated above normal.
At rest arterial oxygen tension, PaO2 (mean 8.1 +/- 1.7 kPa) and mixed venous oxygen tension, PVO2 (3.6 +/- 0.4) were reduced. This enabled an assessment of the contribution of V/Q imbalance to the abnormal gas exchange on the condition. Haemodynamic and gas exchange measurements were made at rest, on supine exercise and on acute vasodilatation with intravenous prostacyclin in eight patients with pulmonary hypertension.
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