Long-term stability of respiratory sinus arrhythmia among adults with and without a history of depression.

Respiratory sinus arrhythmia (RSA) is an index of parasympathetic nervous system activity reflecting respiratory influences on heart rate. This influence is typically measured as high frequency heart rate variability (HF-HRV) or root mean square of successive differences (RMSSD) of adjacent inter-beat intervals. Examining the long-term stability of its measurement is important as levels of resting RSA have been conceptualized as a marker of individual differences; in particular, of an individual's autonomic regulation and affect-related processes, including emotion regulation. At present, it is not known if resting RSA levels reflect stable differences over a long-term period (i.e., >1 year). Even less is known about how RSA stability differs as a function of depression history and whether it relates to depression risk trajectories. In the present study, we examined the 1.5-year test-retest reliability of resting RSA using the intraclass correlation coefficient (ICC) in 82 adults: n = 41 with a history of depression (ever-depressed); n = 41 controls with no depression history (never-depressed). HF-HRV was fairly stable in both groups (ever-depressed ICC = 0.55, never-depressed ICC = 0.54). RMSSD was also fairly stable in ever-depressed adults (ICC = 0.57) and never-depressed controls (ICC = 0.40). ICC values for both indices did not differ between groups per overlapping 95% confidence intervals. Therefore, RSA stability as assessed by both frequency (HF-HRV) and time domain (RMSSD) measures was not attenuated by a depression history. Implications and the need for future research are discussed.