Control mechanisms determining rate and depth of respiratory movements

Abstract

The relationship between ventilation ( E), tidal volume (V T) and frequency (f) was studied in cats under various conditions with and without intact vagus nerves. Ventilation was increased by a rebreathing technique and the respiratory pattern was altered i.a. by thermal and electrical stimulation. With intact vagi the E - V T relationship was similar to that of man (hey et al., 1966). After vagotomy the slope constant became smaller since, in this situation, only V T, but not f, increased with increasing chemical drive. The slope constant increased with increasing temperature from < 35°C and upwards due to a selective increase of f, whether the vagi were intact or cut. It is concluded that the increase in f in response to CO 2 is entirely dependent on the vagal mechanisms, while the bulbopontine pacemaker mechanisms act as the f-govemor when f is selectively increased e.g. by thermal stimulation and decortication. It was confirmed that the rate of increase of inspiratory activity depends on the chemical drive but is independent of the f-determining mechanisms. V T thus depends both on the rate of volume increase and on the part of the f-govemor which determines inspiratory duration.