Physiological changes and compensatory mechanisms by the action of respiratory muscles in a porcine model of phrenic nerve injury

Phrenic nerve damage may occur as a complication of specific surgical procedures, prolonged mechanical ventilation, or physical trauma. The consequent diaphragmatic paralysis or dysfunction can lead to major complications. To elucidate the role of the non-diaphragmatic respiratory muscles during partial or complete diaphragm paralysis induced by unilateral and bilateral phrenic nerve damage at different levels of ventilatory pressure support in an animal model. Ten pigs were instrumented, the phrenic nerve exposed from the neck and spontaneous respiration preserved at three levels of pressure support: high, low and null at baseline condition, after left phrenic nerve damage and bilateral phrenic nerve damage. Breathing pattern, thoraco-abdominal volumes and asynchrony and pressures were measured at each condition. Physiological breathing was predominantly diaphragmatic, homogeneously distributed between right and left sides. After unilateral damage, the paralyzed hemidiaphragm was passively dragged by the ipsilateral ribcage muscles and the contralateral hemidiaphragm. After bilateral damage, the drive to and the work of breathing of ribcage and abdominal muscles increased, to compensate for diaphragmatic paralysis, ensuing paradoxical thoraco-abdominal breathing. Increasing level of pressure support ventilation replaces this muscle group compensation. When the diaphragm is paralyzed (unilaterally and/or bilaterally), there is a coordinated reorganization of non-diaphragmatic respiratory muscles as compensation that might be obscured by high level of pressure support ventilation. Non-invasive thoraco-abdominal volume and asynchrony assessment could be useful in phrenic nerve injured patients to estimate the extent and type of inspiratory muscle dysfunction.