To the editor: Rubin and associates (1) suggest that treatment with nifedipine may be useful in managing patients with primary pulmonary hypertension. Nifedipine was found to decrease total pulmonary resistance and increase both cardiac output and stroke volume. A study in animals (2) has suggested that nifedipine decreases the pulmonary pressor response to hypoxia. No data are given by Rubin and associates on the effect of nifedipine on arterial Po2, alveolar-arterial oxygen tension difference (A-aDo2), or calculated shunt fraction (Qs/Qt).
We recently used nifedipine, 50 mg sublingual over 1 hour, in a patient with primary pulmonary hypertension and found an