IS BREATHING FUNDAMENTALLY A REFLEX PHENOMENON?

¹ Department of Physiology, University of Michigan, Ann Arbor, Michigan

Whether the rhythmic discharge of the respiratory centre is a localised physico-chemical process modified by afferent impulses, or a reflex phenomena modified by chemical conditions, is considered.

Effects of varied combinations of afferent inflow suggest that breathing may be largely a resultant of numerous and various afferent nerve impulses.

The effectiveness of afferent impulses is profoundly influenced by chemical changes capable of modifying breathing. Results indicate depression of excitatory and inhibitory respiratory reflexes by CO₂ saturation and augmentation by CO₂ depletion and anoxemia. These findings are tentatively employed to analyse respiratory phenomena.

The indirect proportionality of rhythm to intrapulmonary pressure is a reflex effect of changing lung volume. Assuming only a single inhibitory vagal reflex, augmentation of this reflex by sodium carbonate could slow the rhythm and depression by CO₂ could accelerate it, at any pulmonary volume. Graded volume change with a dual vagal reflex control could at some point reverse the effects of both CO₃ and CO₂. Experimentally CO₃ retards breathing during inflation, accelerates during deflation and reduces amplitude at neutral volume. CO₂ acceleration during inflation is reversed to retardation during deflation. Lung volume, therefore, importantly determines the mode of response to chemical influences by changing the relative dominance of individual pulmonary reflexes.

Carbonate apnea is not due to lost excitability, but most probably to augmentation of vagal inhibitory reflexes and possibly other stretch reflexes, for saphenous stimulation during apnea produces superexcessive breathing.

Carbon dioxide administrations under otherwise normal conditions may produce its relatively slow breathing by depressing the vagal accelerating function by chemical vagotomy. Anoxemia may produce its relatively rapid breathing by augmenting this function.

The present experiments indicate the great importance of reflexes and their modification through chemical changes and suggest the breathing may be fundamentally a reflex phenomena. On the other hand, they are not necessarily opposed to an automatically discharging centre under the influence of chemical and afferent nerve impulse changes.

It is suggested that the influence of chemical changes on circulatory reflexes may be a factor in the control of circulation.