Slow recovery from voluntary hyperventilation in panic disorder

Objective: 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. Method: Phy siological responses were recorded in 14 patients with PD, 24 patients with SP, and 24 controls during six cycles of 1-minute of fast breathing altern ating with 1 minute of recovery, followed by 3 minutes of fast breathing an d 10 minutes of recovery. Speed of fast breathing was paced by a tone modul ated at 18 cycles/minute, and depth by feedback aimed at achieving an end-t idal pCO(2) of 20 mm Hg. These values were reached equally by all groups. R esults: During fast breathing, PD and SP patients reported more anxiety tha n controls, and their feelings of dyspnea and suffocation increased more fr om baseline. Skin conductance declined more slowly in PD over the six 1-min ute fast breathing periods. At the end of the final 10-minute recovery, PD patients reported more awareness of breathing, dyspnea, and fear of being s hort of breath, and their pCO(2)s, heart rates, and skin conductance levels had returned less toward normal levels than in other groups. Their lower P CO2S were associated with a higher frequency of sigh breaths. Conclusions: PD and SP patients report more distress than controls to equal amounts of h ypocapnia, but PD differ from SP patients and controls in having slower sym ptomatic and physiological recovery. This finding was not specifically pred icted by hyperventilation, cognitive-behavioral, or suffocation alarm theor ies of PD.