Figure 1. Representative electromyogram record from one female subject while awake (left), during the induction of halothane anesthesia when end-tidal halothane concentration was approximately 0.4 MAC (middle), and after achieving a stable 1 MAC end-tidal concentration of halothane (right). Open and closed circles denote the beginning and end of inspiratory gas flow, respectively. Note that there is only transient activation of the transversus abdominis muscle during induction, and that parasternal intercostal and scalene activity is preserved during halothane anesthesia.