The simultaneous comparison of measurements of phrenic nerve conduction, lung volume and inspiratory muscle strength facilitated an evaluation of the functional effects of unilateral phrenic nerve paresis or paralysis. The vital capacity increased when diaphragmatic EMG activity was first obtained. Similarly, inspiratory muscle strength improved, coincident with the first elicitation of a diaphragmatic EMG response. The Pimax was a more sensitive indicator of phrenic nerve recovery than vital capacity. The results of sniff testing demonstrated that despite restoration of phrenic nerve conduction, marked functional impairment of the hemidiaphragm could be present. In two patients, when a CDAP was first elicited, a paradoxic hemidiaphragmatic movement occurred with sniff testing. This may occur because an action potential is dependent on integrity of only a small number of the total nerve fibers making up the phrenic nerve. Normal diaphragmatic descent was subsequently demonstrated with further recovery. ventolin inhaler
The time course of recovery of the phrenic nerve is dependent on the type of injury and the distance over which regeneration must occur. Both demyelination and axonal degeneration may occur with CAB surgery. With mild degrees of demyelination, the remaining myelin lamellae can elongate and cover the demyelinated areas. This recovery occurs rapidly and therefore would not be an explanation for the prolonged abnormalities noted in our five patients.