FURTHER OBSERVATIONS ON THE MODE OF ACTION OF OXYGEN LACK ON RESPIRATION

¹ Department of Physiology, Middlesex Hospital Medical School

1. The effects on respiration of the inhalation of oxygen poor mixtures were examined in chronic denervated cats and rabbits (i.e. animals that had recovered from denervation of the vaso-sensory zones). In the cat, anoxia, if sufficiently marked, depresses respiration both in the anæsthetised and unanæsthetised animal. In the rabbit anoxia depresses breathing only in the anæsthetised animal. In none of the animals did anoxia cause any stimulation of respiration.

2. It is concluded that anoxia stimulates respiration only when the sino-aortic nerves are intact.

3. CO₂, on the other hand, produces considerable respiratory stimulation in chronic denervated preparations.

4. The changes in the arterial blood are described resulting from the inhalation of oxygen poor mixtures in anæsthetised cats with the respiratory centre innervated and denervated. It is shown that the deafferented animal is imperfectly equipped for dealing with such a situation. Further, under these conditions failure of the deafferented respiratory centre occurs when there is approximately twice as much oxygen in the blood as in the case of the normally innervated centre. It is suggested that afferent impulses along the sino-aortic nerves can antagonise to some extent the direct chemical changes produced by anoxia in the respiratory centre.

5. The respiratory stimulation normally produced by carbon monoxide poisoning is absent after section of the vagi and excision of the carotid sinuses.