Effects of Carbonic Anhydrase Inhibition During Acute Hypoxia

¹ From the Department of Physiology-Biophysics, School of Aviation Medicine, USAF, Randolph Air Force Base, Texas

The effects of exposure to a simulated altitude of 20,000 feet in a decompression chamber before and after a single intravenous injection of a carbonic anhydrase inhibitor were observed in five trained unanesthetized dogs. The pulmonary ventilation, alveolar gas exchange and composition and pH, gas tensions and CO₂ content of the arterial blood were observed. The drug, in a single dose of 100 mg/kg, produced the following effects when combined with acute hypoxia: a) hyperventilation greater than that resulting from hypoxia alone, b) a smaller decrement in the alveolar and arterial Po₂ following ascent to altitude, c) a subsequent rise in alveolar and arterial Po₂ if administered after attaining altitude, d) a greater decrement in alveolar Pco₂ following ascent to 20,000 feet, e) a higher arterial blood H-ion concentration than that associated with hypoxia alone and f) a greater decrease in plasma CO₂ content during adjustment to acute hypoxia. Theoretical calculations were made which indicated that the pulmonary capillary blood has a higher pH and a lower plasma CO₂ content than the peripheral arterial blood after administration of the inhibitor.