Alveolar-arterial O₂ differences during artificial respiration in man

¹ Department of Anesthesiology, Columbia University College of Physicians and Surgeons, and The Presbyterian Hospital, New York City

Alveolar-arterial oxygen differences were determined in anesthetized, paralyzed man. Approximately 20% of the determinations showed a Pa-a O₂ of greater than 20 mm Hg. The arterial tension rose an average of 10 mm Hg when the expiratory pressure was increased from –5 to +5 mm Hg. The insertion of a 3-mm orifice expiratory resistance increased the arterial O₂ tension an average of 7 mm Hg. The causes for these variations in arterial O₂ tension and saturation are discussed. The functional residual capacity at +5 and –5 mm Hg expiratory pressure were determined by the nitrogen washout technique. The theoretically expected changes in alveolar O₂ tension due to differences in the functional residual capacity accounted for only a third or less of the experimentally observed changes in arterial saturations and tensions.