THE DUAL EXCITATORY ACTION OF THE VAGAL STRETCH REFLEX

Abstract

Increased intra-pulmonary pressure produced several important respiratory effects throwing light upon the nature of the vagal stretch reflex. 1. The well-known reduced frequency of breathing. 2A prolonged and increasing constriction of the abdomen. 3An increased velocity of the inspiration and expiration of air. Double vagal block during exaggerated vagal stretch reflex activity abolished abdominal constriction and decreased the velocity of both inspiration and expiration while at the same time it increased the depth of breathing. The vagal stretch reflex is apparently an excitatory phenomenon in which each stretch proprioceptive ending drives both the inspiratory and expiratory half centers by virtue of dual connections at the center. Coordinated alternate reflex activation of the 2 half centers is dependent upon reciprocating interconnections. Vagal inhibition of the inspiratory half center is regarded as a secondary response to vagal excitation of the expiratory half center and vice versa. Thus a reduced frequency of breathing produced by an increased vol. of the lungs is explained by an increased activity of the expiratory half center exerting a more powerful reciprocal inhibition of the inspiratory half center. A mechanism is proposed to explain the nature of vagal action and of "rebound.".