Depression is one of the frequent complications following a mild traumatic brain injury (mTBI). Recent research indicated that abnormalities in the autonomic nervous system (ANS) can be evaluated by a noninvasive power spectral analysis of the heart rate variability (HRV). In this study, we investigated whether a frequency-domain analysis of HRV was correlated with late depression in mTBI patients. In total, 181 patients diagnosed with mTBI and 83 volunteers as healthy controls were recruited in 2010-2014. Beck Depression Inventory (BDI) scores were used to evaluate depression in the 1st week of assessment and at 1.5-, 3-, 6-, 12-, and 18-month follow-ups. Correlation and logistic regression analyses of the 1st week HRV parameters with BDI scores at 18 months were performed in individual female mTBI patients. Female mTBI patients were more vulnerable to depression accompanied by reduced HRV compared to healthy controls. Over time, depression was aggravated in female mTBI patients but was alleviated in male mTBI patients. A significantly lower parasympathetic proportion of the ANS was noted at 18 months with respect to the 1st week in female mTBI patients. In addition, depression in female mTBI patients at 18 months after injury was significantly correlated with a decrease in the parasympathetic proportion of the ANS in the 1st week (ρ=-0.411; p < .05). Dysautonomia resulted in higher risks of depression in female mTBI patients. We concluded that early dysautonomia following an mTBI contributes to late depression in female mTBI patients.
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