Influence of Low Oxygen Tension on Pulmonary Circulation After Temporary Arrest of Ventilation in Curarized Dogs

¹ From the Foundation Marie Lannelongue, Paris, France, and the Department of Physiology, University of Minnesota, Minneapolis, Minnesota

The purpose of this study was to investigate the influence of moderate hypoxia on the pulmonary circulation after eliminating the ventilatory response to hypoxia and its secondary effects on the circulation. After Pentothal anesthesia, 10 dogs were fitted with catheters in the pulmonary artery and vein, right atrium and descending aorta. Respiratory arrest was induced by curare-like compounds and mechanical breathing installed. Photokymographic records of pressures and cardiac output determinations were made during artificial respiration and at the end of 90-second periods of ‘apneic oxygenation’ and ‘apneic hypoxia.’ Apneic oxygenation is a period of respiratory arrest following denitrogenation of the animal and during which the trachea is connected to a reservoir containing 100% O₂. Apneic hypoxia is a period of respiratory arrest following ventilation with room air. Both periods were marked by an increase in alveolar pCO₂ not exceeding 20 mm Hg. After 90 seconds of apneic oxygenation mean pulmonary and vein pressure, and pressure gradient between pulmonary artery and vein were significantly lowered. Mean femoral artery was significantly increased. Cardiac output and calculated pulmonary and peripheral resistance were not changed. During apneic hypoxia (with arterial oxygen saturation averaging 46%), mean pulmonary artery, pulmonary vein and femoral artery pressure and pressure gradient between pulmonary artery and vein were significantly increased. Calculated pulmonary and peripheral resistance rose significantly from 2.6 to 3.7 and 40 to 48 mm Hg/l/min., respectively. These increases occurred in the presence of a significant fall in heart rate and in right atrial pressure, and while cardiac output did not change significantly.