Panic symptoms after inhalation of carbon dioxide.

The effects of inhaling a mixture of 35 per cent carbon dioxide and 65 per cent oxygen on the occurrence of panic symptoms defined by the DSM III, was investigated. Compared to a placebo (air), carbon dioxide produced more panic symptoms. If carbon dioxide inhalation was preceded by intake of a beta-blocker (60 mg propranolol), less symptoms occurred than if preceded by a placebo. The results are compared with earlier reports on the effects of lactate infusion. It is argued that panic disorders can be conceptualized as a fear of internal (panic) sensations and that inhalation of a mixture of carbon dioxide and oxygen may constitute an effective exposure treatment.