Acute panic inventory symptoms during CO(2) inhalation and room-air hyperventilation among panic disorder patients and normal controls.

There is scant literature on anxiety symptoms induced during respiratory challenges developed to induce panic symptoms and attacks. Here we report on the prevalence of Acute Panic Inventory (API) symptoms during three consecutive respiratory challenges to patients with panic disorder (PD) and normal controls (NC). The challenges performed using a closed canopy system included voluntary room air hyperventilation (RAH), inhalation of 5% CO(2), and 7% CO(2)-enriched air. The PD patients were 41 men and 53 women whose mean age was 33.4 (SD = 8.55). The normal comparison group consisted of 35 men and 27 women with a mean age of 31.3 (SD = 9.21). The diagnosis of panic disorder was made using the Structured Clinical Interview for DSM-III-R. All potential normal controls underwent structured clinical interview using the Schedule for Affective Disorders and Schizophrenia-Lifetime Version Modified for the Study of Anxiety Disorders (SADS-LA), and must have been free of a lifetime history of anxiety disorders, affective disorders, substance use disorders, and schizophrenia. All participants also had a complete medical evaluation and were in good health. The experiment consisted of seven experimental epochs: three baseline/recovery periods each followed by a respiratory challenge, and then a final recovery epoch. The API was administered at the end of each epoch. Clinical staff trained and experienced in rating panic attacks rated participants' response during each challenge as panic or no panic. Three groups were defined for analysis: PD patients who panicked, PD patients who did not panic, and NC who did not panic. Staff ratings indicated that the 7% CO(2) challenge was the most panicogenic, followed by the 5% CO(2), and the RAH challenges. Conventional statistics (analysis of variance and partial correlations) indicated that many baseline symptoms as well as symptom increments differed across groups, and were associated with the outcome of panic/no panic during each challenge. However, logistic regression analysis indicated that only a few symptoms independently predicted the panic/no panic outcome because many symptoms were redundant. The symptom cluster of fear in general, dizziness, difficulties with concentrating, and doing one's job predicted panic to RAH. The cluster of fear in general, confusion, dyspnea, and twitching/trembling predicted the response to 5% CO(2). Finally, fear in general, confusion, twitching/ trembling and dizziness predicted the response to 7% CO(2). While univariate analyses indicated that many symptoms distinguished between panic and no panic outcome, logistic regression revealed that group differences were subsumed under a few prominent symptoms, namely, fear in general, confusion, dizziness, twitching/trembling, and dyspnea. The results are discussed in the context of patient (having a diagnosis of PD) and panic effects (rated as panicking to a challenge). Copyright 2001 Wiley-Liss, Inc.