The Partial Pressure of Oxygen in the Blood during Progressively Induced Anoxemia

We have studied the passage of oxygen through the pulmonary epithelium during progressively induced anoxemia.’ The dog is remarkably resistant to the effects of a lowered oxygen tension in the inspired air. He will maintain both respiration and an adequate circulation when breathing air containing from 3 to 4 per cent of oxygen. Man, on the other hand, becomes unconscious or “faints” when the oxygen is reduced to between 5 and 8 per cent. Data have not been reported regarding the relationship between the oxygen content of the inspired air which produces unconsciousness in man and that which leads to a stopping of respiration. Comparison, however, indicates that the dog is a most favorable animal for the experimental study of the mechanism controlling the passage of oxygen through the pulmonary epithelium. Two series of experiments were carried out in a study of the problem. Dogs were operated on under chloretone analgesia that did not suppress or weaken either respiratory or vascular reflexes. A “rebreather” apparatus was connected by a short tracheal tube and the animal was allowed progressively to exhaust the oxygen from the air enclosed in the system. The carbon dioxide was absorbed by potassium hydroxide and completely removed from the inhalant air. Graphic records of the blood pressure and the