Autonomic instability during relaxation in panic disorder

The ability to relax was assessed in 14 patients with panic disorder (PD) and 15 non-anxious control subjects for 10 min. Before and after relaxation, subjects performed a standardized activating task of talking continuously for 4 min. The fractional decline in reported anxiety, tension, and alertness between the first talking period and the relaxation minimum did not differ between groups, although absolute levels of anxiety and tension were higher for PD patients. The fractional decline in skin conductance between the first talking period and the last minute of relaxation was less for PD patients than control subjects, while their increase in skin temperature was greater. Skin conductance showed a linear decline over the logarithm of relaxation time, the slope of which was less steep for PD patients. Goodness of fit of skin conductance over log time was also significantly poorer for PD patients. Heart rate levels or slopes did not differ between groups. Autonomic differences between PD and control subjects were largely due to six patients who reported having panic attacks during the test and higher pretest anxiety levels. In conclusion, indicators of relaxation were inconsistent. Skin conductance suggested autonomic instability during quiet sitting in patients who panic or who are prone to panic.