Reflex pulmonary hypertension of fresh-water aspiration

¹ Department of Medicine, University of Sydney, Sydney, N.S.W., Australia

The mechanism of the pulmonary hypertension produced by the aspiration of 1 ml/kg fresh water was investigated in sheep which were intubated and lightly anesthetized with thiopentone. The pulmonary hypertension was reduced by breathing 100% oxygen and by hexamethonium bromide; it was almost completely abolished by atropine sulfate, an infusion of adrenaline or isoproterenol, and by aerosol isoproterenol. Vagotomy, bretylium tosylate, reserpine, acetylcholine by infusion, tetracaine, and lysergic acid butanolamide were ineffective. In most cases aspiration of water produced little change in cardiac output measured by the Fick method. These findings show that aspiration of water excites a local reflex response of the parasympathetic nervous system, producing pulmonary vasoconstriction. The increase in pulmonary artery pressure could not be causally related to the accompanying fall in arterial oxygen saturation or to the change in lung mechanics. The relation of this new form of pulmonary hypertension to the responses of the pulmonary vessels, previously described, is discussed.