Figure 6-19 Effect of increasing halothane on phrenic nerve and neuron activity. With increasing anesthetic depth, both peak phrenic nerve (PPA) and peak neuron activities are depressed. PPA shows the greatest sensitivity to halothane. A, Phrenic nerve activity and the discharge frequency of an inspiratory bulbospinal neuron. Inspiratory (phrenic burst) duration decreases with increasing anesthetic depth. B, Peak expiratory neuron (E), peak inspiratory neuron (I) activity, and PPA. Expiratory neuronal activity was most resistant to the effects of halothane. Bars show the normalized mean ± SEM, and the numbers above the bars indicate the numbers of neurons studied for each condition. (Adapted from Stuth EAE, Tonkovic-Capin M, Kampine JP, et al: Dose-dependent effects of halothane on expiratory and inspiratory bulbospinal neurons and the phrenic nerve activities in dogs. Anesthesiology 81:1470, 1994.)