Increased Bilateral External Intercostal EMG Activity during Tracheal Occlusions (TO) in Conscious Rats with Unilateral Cervical Spinal Cord Injury (c‐SCI)

Abstract

Respiratory motor function after c‐SCI is often studied using anesthetized animal preparations with cervical spinal hemisection (C2HS). However, anesthesia can influence respiratory control, and conscious animal studies of chest wall external intercostal (EI) muscle function after C2HS are lacking. We hypothesized that TO in conscious rats would trigger bilateral recruitment of EI muscles as reflected by increased EMG activity 1 week after C2HS. Adult male Sprague Dawley rats were instrumented with wire EMG electrodes implanted bilaterally in the EI muscles and an inflatable vascular cuff around the extra‐thoracic trachea, 1 week prior to a left C2HS injury. TO trials were presented pre and 1 week post‐C2HS in conscious rats. Trachea was obstructed using cuff inflations for 3–5s followed by normal breathing for 10–15s. Data were collected for 2 min before (Pre‐TO), 20 min during (TO) and 2 min after (Post‐TO) TO trials. Pre‐TO integrated EI (intEI) EMG during eupneic breathing was significantly decreased bilaterally 1 week after C2HS. TO significantly increased bilateral intEI EMG, however, post‐TO intEI responses were variable. Conscious rats were able to significantly augment EI muscle EMG activity when presented with a TO 1 week post‐C2HS injury. Therefore, EI muscles play a significant role in maintenance of minute ventilation both during eupneic and loaded breathing 1 week after C2HS in conscious rats.