Lactate and hyperventilation substantially attenuate vagal tone in normal volunteers. A possible mechanism of panic provocation?

Many aspects of panic attacks, eg, palpitations, tremor, sweating, and an emotional sense of "fear," have been theorized to arise from sympathetic nervous system activation. However, most studies have not demonstrated clearly increased levels of catecholamines during an attack, which is contrary to this hypothesis. To explore another possible cause for the physiological changes known to occur during a panic attack, we assessed parasympathetic nervous system activity by measuring vagal tone during treatments known to produce panic symptoms: sodium lactate administration and hyperventilation. Our findings showed a marked reduction in vagal tone during both procedures. We postulate that withdrawal of parasympathetic activity may explain some of the physiological changes occurring in panic attacks and be contributing to the origin of panic.