Diaphragm and Intercostal Muscle Activity following Unilateral Mid‐cervical Spinal Cord Contusion in the Rat

Abstract

The present study was designed to investigate the diaphragm and intercostal muscle activity following unilateral mid‐cervical spinal cord contusion in rats. Adult male rats were received laminectomy or unilateral contusion at C3–C4 spinal cord using the MASCIS Impactor (height: 6.25 mm). The respiratory airflow and bilateral diaphragm and T2 intercostal muscle electromyogram (EMG) activity were measured during hyperoxia (50 % O2 and 50 % N2) and hypoxia (12.5 % O2) at 3 day, 2 weeks and 8 weeks following spinal surgery. The respiratory frequency was similar between uninjured and contused animals; however, the tidal volume was significant lower in contused animals than uninjured animals at three time points post‐injury. At 3 days post‐injury, the burst amplitude of the contralateral diaphragm EMG was enhanced in contused animals. When the data were normalized by the maximal response during the hypoxic challenge, the ipsilateral diaphragm EMG value of contused animals was greater than that of uninjured animalsat 3 days and 2 weeks post‐injury. At 8 weeks post‐injury, there were no significant differences in the diaphragm EMG activity between uninjured and contused animals. Notably, the intercostal muscle activity was not substantially influenced by mid‐cervical contusion from acute to chronic injury state. These results suggested that mid‐cervical spinal contusion induced a compensatory increase in contralateral diaphragmatic activity and resulted in greater utilization of percentage of maximal inspiratory activity of the ipsilateral diaphragm. The maintenance of intercostal activity may enable the animal to sustain the essential breathing capacity following injury.Support or Funding InformationNHRI‐EX105‐10223NC, MOST 105‐2628‐B‐110‐002‐MY3