Biological challenge manipulation of PCO2 levels: a test of Klein's (1993) suffocation alarm theory of panic.

D.F. Klein (1993) proposed that patients with panic disorder (PD) have a hypersensitive suffocation monitor that predisposes them to experience panic attacks under certain conditions. The suffocation alarm theory predicts differential emotional responding to biological challenges that affect arterial partial pressure of carbon dioxide (PCO2). These PD patients should exhibit (a) lower fear and less likelihood of panic in response to biological challenges that lower PCO2 levels (e.g., hyperventilation), and (b) increased fear and greater likelihood of panic in response to biological challenges that raise PCO2 levels (e.g., inhalation of 35% CO2 gas). The following indicators of the suffocation monitor were assessed: (a) severity of dyspnea symptoms, (b) frequency of dyspnea symptoms, (c) heightened respiration rate, and (d) lowered PCO2 levels. Ratings of physiological and subjective responding, as well as panic, were obtained during both a hyperventilation and a 35% CO2 challenge. None of the classification methods predicted differential emotional responding to hyperventilation versus 35% CO2 challenge.