Cardiac and respiratory activity in panic disorder: Effects of sleep and sleep lactate infusions

Objective: This study examined cardiac and respiratory activity in panic disorder patients and healthy comparison subjects during sleep, when the effects of anxious cognition and expectancy set are minimized. Method: Heart rate, respiratory rate, end-tidal PCO₂, and oxygen saturation were recorded for 11 panic disorder patients and 12 comparison subjects before and during sleep and before and after infusions of sodium lactate and a saline control. Results: Panic disorder patients had higher oxygen saturations than comparison subjects before sleep onset and during sleep stages 0 and 2 before any infusions. The two groups did not differ on other respiratory variables and heart rate. Panic disorder patients responded to lactate infusions during stage 3-4 sleep with greater increases in heart rate and oxygen saturation, and possibly in respiratory rate and end-tidal PCO₂, than comparison subjects. The saline control infusion had little effect. Conclusions: These findings suggest that panic disorder patients have greater cardiac and respiratory reactivity than healthy comparison subjects during sleep, when the influence of cognitive factors is minimal or absent.