Cervical spinal cord hemisection impacts sigh and the respiratory reset in male rats.

Cervical spinal cord injury impacts ventilatory and non-ventilatory functions of the diaphragm muscle (DIAm) and contributes to clinical morbidity and mortality in the afflicted population. Periodically, integrated brainstem neural circuit activity drives the DIAm to generate a markedly augmented effort or sigh-which plays an important role in preventing atelectasis and thus maintaining lung function. Across species, the general pattern of DIAm efforts during a normal sigh is variable in amplitude and the extent of post-sigh "apnea" (i.e., the post-sigh inter-breath interval). This post-sigh inter-breath interval acts as a respiratory reset, following the interruption of regular respiratory rhythm by sigh. We examined the impact of upper cervical (C 2 ) spinal cord hemisection (C 2 SH) on the transdiaphragmatic pressure (P di ) generated during sighs and the post-sigh respiratory reset in rats. Sighs were identified in P di traces by their characteristic biphasic pattern. We found that C 2 SH results in a reduction of P di during both eupnea and sighs, and a decrease in the immediate post-sigh breath interval. These results are consistent with partial removal of descending excitatory synaptic inputs to phrenic motor neurons that results from C 2 SH. Following cervical spinal cord injury, a reduction in the amplitude of P di during sighs may compromise the maintenance of normal lung function.