Figure 1. Changes in phrenic nerve activity during systemic hyperoxia (controls 1 and 2) and hypoxia (hypoxia) at three levels of end-tidal halothane concentration with intact carotid sinus nerve (A)(protocol 1) and chemodenervation (B)(protocol 2). Phrenic nerve activity is expressed as a percentage of the value of control 1 at halothane, 0%. *P <0.05 compared with halothane, 0%. #P < 0.05 compared with halothane, 0.1%. $P < 0.05 compared with controls 1 and 2.