Mid-cervical spinal cord contusion causes robust deficits in respiratory parameters and pattern variability


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Abstract

Mid-cervical spinal cord contusion disrupts both the pathways and motoneurons vital to the activity of inspiratory muscles. The present study was designed to determine if a rat contusion model could result in a measurable deficit to both ventilatory and respiratory motor function under “normal” breathing conditions at acute to chronic stages post trauma. Through whole body plethysmography and electromyography we assessed respiratory output from three days to twelve weeks after a cervical level 3 (C3) contusion. Contused animals showed significant deficits in both tidal and minute volumes which were sustained from acute to chronic time points. We also examined the degree to which the contusion injury impacted ventilatory pattern variability through assessment of Mutual Information and Sample Entropy. Mid-cervical contusion significantly and robustly decreased the variability of ventilatory patterns. The enduring deficit to the respiratory motor system caused by contusion was further confirmed through electromyography recordings in multiple respiratory muscles. When isolated via a lesion, these contused pathways were insufficient to maintain respiratory activity at all time points post injury. Collectively these data illustrate that, counter to the prevailing literature, a profound and lasting ventilatory and respiratory motor deficit may be modelled and measured through multiple physiological assessments at all time points after cervical contusion injury.HIGHLIGHTSCervical contusion causes reduction in ventilatory function and muscle activity from acute to chronic time-points.Contusion reduces the variance of the ventilatory waveform during eupnea which is sustained until chronic time points.Endogenous recovery is limited following cervical contusion, but modest amounts may be mediated through spared tissue.These findings highlight novel ways to assess the profound deficit caused to respiratory output following spinal injury.

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