Effects of breathing carbon dioxide upon the pulmonary circulation.

IN THE 2 companion papers, we have considered some effects of acute hypoxia on the pulmonary circulation. The present study, concerned with the effects of acute hypercapnia on the pulmonary eirculation, was prompted by 2 prospects: (1) that an acute increase in alveolar and arterial P 0, brought about by the inhalation of air enriched with carbon dioxide, might simulate the effects on the pulmonary circulation of the chronic hypereapnia of alveolar hypoventilation, and (2) that regional variations in alveolar ventilation may, through local increments in carbon dioxide tension, change local vascular resistances so as to divert pulmonary arterial blood to better ventilated alveoli.' The effects of inhaling carbon dioxide mixtures on the pulmonary circulation has been investigated by others'-6 with inconsistent results. The present report deals with the effects of an acute increase in the carbon dioxide tension (PCO2) of inspired air on pulmonary blood flow and pressures in normal man and in patients with chronic pulmonary emphysema. Methods All tests were performed in the postabsorptive state, without medication. Venous catheterization of the right heart was performed in the usual way and the tip of the catheter was placed in the main pulmonary artery. An indwelling arterial needle was inserted into the right brachial artery. After the catheter and needle were in place, the patient