Unilateral diaphragm muscle paralysis minimally impacts ventilation in rodents (871.5)

Abstract

Ventilatory behaviors across a range of species including humans require less than 50% of maximal force‐generating capacity by the diaphragm muscle, the main inspiratory muscle in mammals. Near maximal forces are only generated during expulsive behaviors usually associated with airway clearance. There is ongoing controversy regarding the impact of unilateral lesions (e.g., spinal cord injury, denervation) on ventilatory outcomes. We hypothesized that unilateral denervation of the diaphragm muscle in rats and mice would minimally impact ventilation. Transdiaphragmatic pressure (Pdi) measurements were used to estimate diaphragm muscle force in adult male rats and mice. Following acute, unilateral phrenic nerve transection in the neck, there was no change in Pdi during eupnea or hypoxia‐hypercapnia in rats or mice. Reduced Pdi was evident during deep breaths and tracheal occlusion (behaviors associated with ~70% of maximal Pdi elicited by bilateral phrenic nerve stimulation) in both species. These results are also consistent with the lack of changes in tidal volume or respiratory pattern during eupnea measured by whole body plethysmography in unrestrained, spontaneously breathing rats after mid‐cervical contusion or hemisection injuries. These results highlight the large reserve capacity for force generation by the diaphragm muscle in rodents and the importance of measuring multiple motor behaviors.Grant Funding Source: Supported by HL096750, AG044615, HL105355 and Mayo Center for Regenerative Medicine