SYMPATHETIC ACTIVITY IN PATIENTS WITH PANIC DISORDER AT REST, UNDER LABORATORY MENTAL STRESS, AND DURING PANIC ATTACKS

Background: The sympathetic nervous system has long been believed to b e involved in the pathogenesis of panic disorder, but studies to date, most using peripheral venous catecholamine measurements, have yielded conflicting and equivocal results. We tested sympathetic nervous func tion in patients with panic disorder by using more sensitive methods. Methods: Sympathetic nervous and adrenal medullary function was measur ed by using direct nerve recording (clinical microneurography) and who le-body and cardiac catecholamine kinetics in 13 patients with panic d isorder as defined by the DSM-IV, and 14 healthy control subjects. Mea surements were made at rest, during laboratory stress (forced mental a rithmetic), and, for 4 patients, during panic attacks occurring sponta neously in the laboratory setting. Results: Muscle sympathetic activit y, arterial plasma concentration of norepinephrine, and the total and cardiac norepinephrine spillover rates to plasma were similar in patie nts and control subjects at rest, as was whole-body epinephrine secret ion. Epinephrine spillover from the heart was elevated in patients wit h panic disorder (P = .01). Responses to laboratory mental stress were almost identical in patient and control groups. During panic attacks, there were marked increases in epinephrine secretion and large increa ses in the sympathetic activity in muscle in 2 patients but smaller ch anges in the total norepinephrine spillover to plasma. Conclusions: Wh ole-body and regional sympathetic nervous activity are not elevated at rest in patients with panic disorder. Epinephrine is released from th e heart at rest in patients with panic disorder, possibly due to loadi ng of cardiac neuronal stores by uptake from plasma during surges of e pinephrine secretion in panic attacks. Contrary to popular belief, the sympathetic nervous system is not globally activated during panic att acks.