Analysis of ventilatory response to CO₂ during hypoxia in dogs

¹ Department of Physiology, Kanazawa University School of Medicine, Kanazawa, Japan

The response of the respiratory apparatus to CO₂ during acute oxygen want was investigated in anesthetized dogs. The ratio of elevated ventilation to unit increase of Pa_COCO2 in hypoxia to that in normoxia (SR) was taken as a measure of interaction between hypoxia and hypercapnia. Furthermore, the separate effect on ventilation by Pa_COCO2 (AVR/Pco₂) and [H⁺] (AVR/H) during hypoxic hypercapnia was evaluated. a) SR increased in the presence of mild anoxia (80–50 mm Hg of Pa_OO2), then decreased in severe anoxia (less than 50 mm Hg of Pa_OO2). b) AVR/Pco₂ showed a higher value than the normoxia level in mild hypoxia (80–55 mm Hg of Pa_OO2), then progressively decreased with a further development of anoxia. c) AVR/H started increasing at about 70 mm Hg of Pa_OO2, then increased as the Pa_OO2 decreased, and reached about four times the normal at 30–40 mm Hg of Pa_OO2. The marked difference between isolated Pco₂ and [H⁺] effect on ventilation in severe hypoxia suggested different areas and actions in the respiratory system of both chemical agents.

Submitted on September 3, 1964