NIFEDIPINE DILATES THE PULMONARY VASCULATURE WITHOUT PRODUCING SYMPTOMATIC SYSTEMIC HYPOTENSION IN UPRIGHT RESTING AND EXERCISING PATIENTS WITH PULMONARY-HYPERTENSION SECONDARY TO CHRONIC OBSTRUCTIVE PULMONARY-DISEASE

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Abstract
Vasodilator therapy may lower pulmonary vascular resistance in patients with chronic air-flow limitation. However, the effects of these agents on left ventricular afterload, cardiac output, and bronchial smooth muscle could lower the calculated pulmonary vascular resistance without specifically affecting pulmonary vascular tone. In addition, systemic hypotension in the upright position and worsening ventilation/perfusion heterogeneity could limit their use. We determined the pulmonary driving pressure (pulmonary arterial-pulmonary arterial wedge pressure) to flow relationship, as well as the transmural pulmonary arterial pressure in 9 patients with severe chronic air-flow limitation with pulmonary hypertension while in a clinically stable condition. Measurements were made at rest and during 3 stages of progressively increasing upright exercise on a bicycle before and after a single 20-mg dose of nifedipine. Nifedipine displaced both the driving pressure to flow and the pulmonary arterial transmural pressure to flow relationships towards higher flows in every subject, suggesting an active vasodilation. In the upright position, PaO2 did not change, and the systemic arterial pressure was only mildly reduced. In patients with pulmonary hypertension from chronic air-flow limitation, acute administration of nifedipine to upright patients causes pulmonary, as well as systemic vasodilation without causing symptomatic hypotension or reducing arterial oxygenation.