Chest muscle activity and panic anxiety: a preliminary investigation.

This report represents a pilot investigation of the role of chest muscle electromyographic (EMG) activity in developing panic episodes. Chest EMG activity was obtained as part of a larger study examining ventilatory differences between panic sufferers and normal controls. Frontalis EMG, heart rate, and minute ventilation (breathing rate and tidal volume) were also obtained during the study. The ventilatory procedure involved exposing the subjects to three periods of carbon dioxide gas inhalations (1%, 3%, 5%; balance oxygen). Subjective measures of frightening cognitions and body sensations were obtained across the inhalation phases as well. The panic disorder subjects were divided, on the basis of subjective anxiety ratings obtained throughout the study, into high anxious (HA) and low anxious (LA) panic disorder groups. The HA panic disorder patients exhibited significantly higher chest EMG activity than the LA panic disorder patients and controls across all phases of the experiment. In addition, the chest EMG predicted, better than the other physiologic measures, the number of frightening cognitions and sensations reported by the subjects during the baseline and 5% CO2 inhalation phases. Overall, the results were supportive of the further study of chest wall EMG activity in the pathogenesis of panic attacks.