FIG. 3.

Time course of diaphragm compound muscle action potentials (CMAPs) and ventilatory parameters using whole-body plethysmography following unilateral C4 cervical contusion. Compared with laminectomy-only uninjured animals (B), C4 injured rats (C) had reduced CMAP amplitudes in ipsilateral hemidiaphragm following phrenic nerve stimulation, a functional electrophysiological assay of phrenic motor neuron (PhMN) innervation of the diaphragm. Significantly decreased peak CMAP amplitudes were observed at all time points post-injury, with a trend toward improvement at 8 and 14 days post-injury (DPI) (A). Using whole-body plethysmography, respiratory rate (D), tidal volume (E), inspiratory and expiratory duration (F,G), and peak inspiratory flow (H) were determined under normoxic conditions repeatedly on the same animals before and after spinal cord injury (SCI). Respiratory rate significantly increased at 1 DPI in injured rats compared to uninjured controls and returned to pre-injury baseline at 4, 8 and 14 DPI (D). Similarly, significant changes in tidal volume (E), expiratory time (G) and peak inspiratory flow (H) were transient in injured rats, with differences observed only at 1 DPI. No differences were measured for inspiratory time (F) or minute ventilation (not shown). Results are expressed as means±SEM. Statistical significance was assessed by analysis of variance (one-way ANOVA) and multiple comparisons post-hoc test (Bonferroni's method). **DPI versus uninjured (p<0.01); ***DPI versus uninjured (p<0.001). n=5 animals for uninjured group and for injured animals at 1, 8, and 14 DPI; n=9 animals for injured animals at 4 DPI.