Autonomic function in the early stage of panic disorder: Power spectral analysis of heart rate variability

Previous studies of autonomic nervous system (ANS) function in panic disord er (PD) patients have yielded conflicting results. We speculate that these differences might result from the variety of clinical stages of PD, In orde r to investigate this, we compared ANS activity in untreated patients in th e early stage of PD with control subjects using power spectral analysis of electrocardiogram R-R intervals (PSR-R) in supine rest and during head-up t ilt, which was performed according to the maximum entropy method (MEM). It recognizes two main components: high-frequency power (HF), which mainly ref lects cardiac parasympathetic activity, and low-frequency power (LF), which reflects both cardiac sympathetic and parasympathetic activity. The patien ts with PD had significantly higher values for all components of PSR-R only in tilt position total power (TP), LF, and HF than did the control subject s (P < 0.01, <0.01, <0.02, respectively). However, the LF/HF ratio which in dicated sympathovagal balance did not differ significantly between the two groups in tilt position. Our findings suggest that patients with PD in the early stage of illness have co-activation of sympathetic and parasympatheti c nervous systems, which might act to maintain a balance between the two au tonomic systems.