Because hyperventilation has figured prominently in theories of panic disorder (PD) but not of social phobia (SP), we compared predictions regarding diagnosis-specific differences in psychological and physiological measures before, during, and after voluntary hyperventilation.
Physiological responses were recorded in 14 patients with PD, 24 patients with SP, and 24 controls during six cycles of 1-minute of fast breathing alternating with 1 minute of recovery, followed by 3 minutes of fast breathing and 10 minutes of recovery. Speed of fast breathing was paced by a tone modulated at 18 cycles/minute, and depth by feedback aimed at achieving an end-tidal pCO2 of 20 mm Hg. These values were reached equally by all groups.
During fast breathing, PD and SP patients reported more anxiety than controls, and their feelings of dyspnea and suffocation increased more from baseline. Skin conductance declined more slowly in PD over the six 1-minute fast breathing periods. At the end of the final 10-minute recovery, PD patients reported more awareness of breathing, dyspnea, and fear of being short of breath, and their pCO2s, heart rates, and skin conductance levels had returned less toward normal levels than in other groups. Their lower pCO2s were associated with a higher frequency of sigh breaths.
PD and SP patients report more distress than controls to equal amounts of hypocapnia, but PD differ from SP patients and controls in having slower symptomatic and physiological recovery. This finding was not specifically predicted by hyperventilation, cognitive-behavioral, or suffocation alarm theories of PD.
From the Department of Psychiatry and Behavioral Sciences, Stanford University, Stanford and the Department of Veterans Affairs Health Care System, Palo Alto, California. Dr. Gerlach is currently at the Westfälische Wilhelms-Universität Münster, Germany.
Address reprint requests to: Frank Wilhelm, Stanford University/VAPAHCS (116F-PAD), 3801 Miranda Ave., Palo Alto, CA 94304. Email: email@example.com
Received for publication September 27, 1999; revision received October 23, 2000.