Reflex control of abdominal muscles during positive-pressure breathing

Abstract

Continuous positive-pressure breathing initiates expiratory activity in the abdominal muscle and inhibits the diaphragm in anesthetized cats. This investigation defines neural mechanisms involved in this abdominal muscle response (AMR) to positive-pressure breathing. The AMR is not a segmental reflex since it is abolished by thoracic spinal transection. Bilateral rhizotomy (T8-L3) also eliminates AMR, but laparotomy and abdominal evisceration do not, suggesting that some neural inflow other than from abdominal muscle or viscera is necessary but insufficient for maintaining AMR. Abdominal vagotomy failed to interrupt AMR which was abolished by bilateral cervical vagotomy, indicating that the necessary receptors lie in the thorax. Compression or local anesthesia of the cervical vagi provided the experimental means for abolishing either the inhibition of the diaphragm or the AMR without necessarily interrupting the other. That one response may persist in the absence of the other indicates that vagal afferent pathways subserving AMR are distinct from those mediating diaphragm inhibition. Hence the active expiration of pressure breathing is not a simple corollary of the Hering-Breuer inflation reflex but is a separate reflex served by its own vagal pathway. abdominal muscle response; vagus control of active expiration; abdominal muscle motoneuron pool; vagal afferent pathway in pressure-breathing reflex; thoracic receptors; diaphragm response to pressure breathing; diaphragm; inspiration; expiratory reflexes; inspiratory reflexes; respiratory reflexes; segmental reflexes; spinal reflexes Submitted on February 21, 1963