Effects of Drugs on the Pulmonary Circulation and Ventilation as Reflected by Changes in the Arterial Oxygen Saturation

The effect of: l -epinephrine, acetylcholine, histamine, aminophylline, and serotonin on Ihe pulmonary circulation and ventilation was studied in anesthetized dogs. The following observations were noted: Serotonin produced an increase in arterial oxygen saturation, the other drugs a decrease. Although reduced, the effect was not eliminated by controlling the volume of ventilation or by the inhalation of 25 or 30 percent oxygen. The administration of 100 percent oxygen eliminated the response in all dogs studied. The effect was not abolished by controlling blood flow in addition to ventilation. Changes in the over-all ventilation/perfusion ratio appeared of major importance. In addition, these drugs apparently produced local changes in ventilation/perfusion ratios (physiologic shunting) and/or in the degree of anatomic intrapulmonary shunting of blood. The effects of changes in pulmonary blood flow on peripheral arterial oxygen saturation were also investigated. With the volume of ventilation constant, the following was observed : Increasing pulmonary blood flow by whatever means decreased SaO 2 ; decreasing blood flow resulted in an increase in SaO 2 .