Diminished vagal activity and blunted circadian heart rate dynamics in posttraumatic stress disorder assessed through 24-h linear and unifractal analysis

Background : Affected autonomic heart regulation is implicated in the pathophysiology of cardiovascular diseases and is also associated with posttraumatic stress disorder (PTSD). However, although sympathetic hyperactivation has been repeatedly shown in PTSD, research has neglected the parasympathetic branch. The objective of this study is the long-term assessment of heart rate (HR) dynamics and its circadian changes as an index of autonomic imbalance in PTSD. Since tonic parasympathetic activity underlies long-range correlation of heartbeat interval fluctuations in healthy state, we included nonlinear (unifractal) analysis as an important and sensitive readout to assess functional alterations. Methods : Electrocardiogram recordings over a 24-h period were conducted in 15 deployed male subjects with moderate to high levels of combat exposure (PTSD: n=7; combat controls: n=8). Analysis of HR dynamics included time domain, frequency domain and non-linear analysis based on detrended fluctuation analysis. Psychiatric symptoms were assessed using structured interviews, including the Clinician Administered PTSD Scale. Results : Subjects with PTSD showed significantly higher baseline HR, higher LF/HF ratio in frequency domain analysis, blunted differences between daytime and nighttime measures, as well as higher scaling coefficient αfast during the day, indicating diminished tonic parasympathetic activity. Conclusions : This study appears to be the first combining linear and non-linear methods to assess long-period autonomic and circadian differences in HR dynamics between combatants with and without PTSD. Diminished circadian differences and blunted tonic parasympathetic activity altering HR dynamics suggest central neuro-autonomic dysregulation that could represent a possible link to increased cardiovascular mortality in PTSD.