Autonomic nervous system (ANS) dysregulation in depression is associated with symptoms associated with the ANS. The beat-to-beat pattern of heart rate defined as heart rate variability (HRV) provides a noninvasive portal to ANS function and has been proposed to represent a means of quantifying resting vagal tone. We quantified HRV in bipolar depressed (BDD) patients as a measure of ANS dysregulation seeking to establish HRV as a potential diagnostic and prognostic biomarker for treatment outcome. Forty-seven BDD patients were enrolled. They were randomized to receive either escitalopram–celecoxib or escitalopram-placebo over 8 weeks in a double-blind study design. Thirty-five patients completed the HRV studies. Thirty-six healthy subjects served as controls. HRV was assessed at pretreatment and end of study and compared with that of controls. HRV was quantified and corrected for artifacts using an algorithm that incorporates time and frequency domains to address non-stationarity of the beat-to-beat heart rate pattern. Baseline high frequency-HRV (i.e., respiratory sinus arrhythmia) was lower in BDD patients than controls, although the difference did not reach significance. Baseline low-frequency HRV was significantly lower in BDD patients (ln4.20) than controls (ln = 5.50) (p < 0.01). Baseline heart period was significantly shorter (i.e., faster heart rate) in BDD patients than controls. No significant change in HRV parameters were detected over the course of the study with either treatment. These findings suggest that components of HRV may be diminished in BDD patients.

Reduced vagal tone and higher levels of inflammatory biomarkers may distinguish BD from MDD and reveal an underlying pathophysiology of depression involving ANS dysfunction and chronic immune system dysregulation.

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Aims: Autonomic nervous system (ANS) dysregulation is associated with various symptoms of depressive disorder. The beat-to-beat pattern of heart rate (Heart Rate Variability) (HRV) provides a noninvasive portal to ANS function through the quantification of periodic heart rate patterns. In this study we quantified two components of HRV: Respiratory Sinus Arrhythmia (RSA), and Low Frequency HRV (LF-HRV). Both of these components have been extensively reported in studies of depression and have been at least partially associated with reduction in vagal nerve tone. We quantified RSA and LF-HRV in patients with Major Depressive Disorder (MDD) as measures of ANS regulation seeking to establish the utility of components of HRV as potential diagnostic and prognostic biomarkers for treatment outcome. Methods: Sixty-six MDD patients were enrolled. In two separate and consecutively run studies they received either Escitalopram or Quetiapine fumarate ER over 12 weeks. Forty-one patients completed the studies. RSA and LF-HRV were assessed at pretreatment and end of study. Thirty-six healthy subjects served as controls. RSA and LF-HRV were quantified using an algorithm that incorporates time and frequency domains to address the non-stationarity of the beat-to-beat heart rate pattern. Results: No significant differences in baseline RSA or LF-HRV were found between MDD and healthy controls. However, baseline RSA and LF-HRV were significantly higher in treatment responders (lnRSA = http://jpbs.qingres.com

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