Effects of intrapleural pressure on phrenic nerve activity.

In order to evaluate the effect of changing respiratory mechanics on the relation between respiratory mechanical output and phrenic activity, we simultaneously measured ventilatory output from the trace of pneumotachograph and changes in phrenic nerve activity before and after pneumothorax in alpha-chloralose anesthetized dogs. After pneumothorax, the dynamic lung compliance, inspiratory duration and tidal volume were decreased significantly, whereas the integrated peak amplitude and the rate of rise of phrenic neural output were increased substantially. The difference between respiratory mechanical output and phrenic activity was also significant (p less than 0.05). As shown from the results, the increase of phrenic response to pneumothorax may be mediated through intrapulmonary receptors along the vagal afferent rather than through the changes in chemical drive.