Figure 6. (A) Effect of isocapnic hypoxia on phrenic nerve activity (PNG) during 1 MAC halothane anesthesia and 90 min after replacement of halothane with intravenous STP anesthesia. The two anesthetics have strikingly different effects on neural phase timing, but the hypoxic stimulus caused a comparable increase in peak phrenic activity with both anesthetics. O²(%), airway oxygen concentration. (B) Pooled peak phrenic activity (PPA) data versus Pa^O2of the four animals subjected to the hypoxic stimulus with two different anesthetics (protocol 3). There were no significant differences between the net phrenic hypoxic responses for the two anesthetics. STP = sodium thiopental; HAL = halothane.