Abstract
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.