In four healthy subjects and four patients with lung disease, hemodynamic studies were done during two periods of identical exercise, 1 hr apart. Pulmonary artery pressure was lower in the second exercise period in all subjects studied. Pulmonary arterial wedge pressure was measured in four cases and was unchanged or even slightly increased. The “total pulmonary” and pulmonary vascular resistances were markedly lower in the second exercise period. The decrease in pulmonary artery pressure was found also in the second postexercise period when compared with the starting resting level. It is believed that this fall in pulmonary artery pressure and resistance was due to opening or widening of previously closed or constricted lung vessels. Repeated exercise must be used with caution when studying the effect of pharmacological or physiological agents on the lesser circulation. Submitted on November 30, 1962
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