ACTION OF HYPERCAPNIA DURING HYPOXIA ON PULMONARY VESSELS

  • 1 January 1977
    • journal article
    • research article
    • Vol. 13  (6) , 763-776
Abstract
Two opposing actions of CO2 on pulmonary vessels, vasoconstriction and vasodilatation, were studied in dogs, cats, ferrets and rats using isolated lungs or a lobe of lung in vivo. Both preparations were perfused at a constant flow rate so that changes in inflow pressure at constant outflow pressure represented changes in vascular resistance. Lungs were ventilated with 5-15% CO2 during hypoxic vasoconstriction to permit demonstration of dilatation and because the 2 stimuli frequently concur. During hypoxia CO2 caused further constriction, dilatation or a biphasic response. Only constriction occurred in dogs and only dilatation in rats. Constriction predominated in cats but dilatation sometimes occurred in later tests in isolated lungs and after a carbonic anhydrase inhibitor. All 3 responses were seen in ferrets. The type of response did not depend on CO2 concentration. In rats dilatation turned to constriction after .beta.-adrenoreceptor blocking drugs. The vessels affected by dilatation could not be determined. CO2 can enhance or diminish the action of hypoxia, but the circumstances determining one or the other action are not resolved.