Respiratory sinus arrhythmia as a predictor of outcome in major depressive disorder

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Background: Respiratory sinus arrhythmia (RSA) is a noninvasive measure of parasympathetic tone that has been related to emotion regulatory capacity. While some previous work indicates that clinically depressed persons exhibit lower levels of RSA than do normal controls, there is nevertheless considerable between-subject variation in RSA among depressed persons. The current study evaluated the significance of variation in RSA among depressed persons by examining whether levels of RSA predicted concurrent symptomatology and the course of depressive illness. Methods: The RSA levels of 55 diagnosed depressed individuals were assessed during a paced breathing procedure at Time 1. Six months later (Time 2), participants were interviewed again to determine whether or not each had fully recovered from depression. Multinomial regression analyses were conducted to examine whether RSA predicted Time 2 clinical status. Results: Although RSA levels were not related to overall depression severity, they were associated with specific symptoms of depression: RSA was positively associated with the report of sadness and negatively associated with the report of suicidality. More strikingly, however, higher levels of RSA at Time 1 predicted non-recovery from depression at Time 2, even when statistically controlling for initial depression severity, age and medication use. Limitations: Treatment and medication use were not controlled during the follow-up period and a group of nonpsychiatric controls was not included in this study. Conclusions: A relatively high level of RSA among depressed individuals predicts a more pernicious course of illness than do lower RSA levels.