Impact of cervical spinal cord contusion on the breathing pattern across the sleep-wake cycle in the rat.

The present study was designed to investigate breathing patterns across the sleep-wake state following a high cervical spinal injury in rats. The breathing patterns (e.g., respiratory frequency, tidal volume and minute ventilation), neck electromyogram (EMG), and electroencephalography (EEG) of unanesthetized adult male rats were measured at the acute (i.e., one day), subchronic (i.e., two weeks), and/or chronic (i.e., six weeks) injured stages after unilateral contusion of the 2nd cervical spinal cord. Cervical spinal cord injury caused a long-term reduction in the tidal volume, but did not influence the sleep-wake cycle duration. The minute ventilation during sleep was usually lower than that during the wake period in uninjured animals due to a decrease in respiratory frequency. However, this sleep-induced reduction in respiratory frequency was not observed in contused animals at the acute injured stage. By contrast, the tidal volume was significantly lower during sleep in contused animals but not uninjured animals from the acute to the chronic injured stage. Moreover, the frequency of sigh and post-sigh apnea was elevated in acutely contused animals. These results indicated that high cervical spinal contusion is associated with exacerbated sleep-induced attenuation of the tidal volume and higher occurrence of sleep apnea, which may be detrimental to respiratory functional recovery after cervical spinal cord injury.