The effect of a new calcium antagonist, felodipine, on pulmonary hypertension and gas exchange in chronic obstructive lung disease.

In 10 patients with advanced chronic lung disease and pulmonary hypertension central haemodynamics and pulmonary gas exchange were studied at rest and during exercise, before and during continuous infusion of the calcium antagonist felodipine, which lowers vascular resistance by selective action on vascular smooth muscle. Pulmonary and systemic vascular resistance were reduced by 20% and 35% respectively. Cardiac output was increased by 28% and pulmonary vascular pressures remained essentially unaltered. Gas exchange measurements revealed an increased shunt, an addition of lung regions with high ventilation/perfusion ratios and a further reduction of arterial oxygenation from 8.5 to 7.9 kPa (64 to 59 mmHg). During exercise, infusion of felodipine resulted in a higher cardiac output and a smaller increase in pulmonary vascular pressure than before felodipine. Arterial oxygenation fell to the same extent as during exercise before felodipine. It is concluded that felodipine lowers pulmonary vascular resistance but at the expense of a worsening of the ventilation-perfusion ratio.