The prevalence of major depressive disorder (MDD) is highest in young adults and contributes to an increased risk of developing future cardiovascular disease (CVD). However, the underlying mechanisms remain unclear. The studies examining cardiac autonomic function that have included young unmedicated adults with MDD report equivocal findings, and few have considered the potential influence of disease severity or duration. We hypothesized that heart rate variability (HRV) and cardiac baroreflex sensitivity (BRS) would be reduced in young unmedicated adults with MDD (18-30 yr old) compared with healthy nondepressed young adults (HA). We further hypothesized that greater symptom severity would be related to poorer cardiac autonomic function in young adults with MDD. Heart rate and beat-to-beat blood pressure were continuously recorded during 10 min of supine rest to assess HRV and cardiac BRS in 28 HA (17 female, 22 ± 3 yr old) and 37 adults with MDD experiencing current symptoms of mild-to-moderate severity (unmedicated; 28 female, 20 ± 3 yr old). Neither HRV [root mean square of successive differences between normal heartbeats (RMSSD): 63 ± 34 HA vs. 79 ± 36 ms MDD; P = 0.14] nor cardiac BRS (overall gain, 21 ± 10 HA vs. 23 ± 7 ms/mmHg MDD; P = 0.59) were different between groups. In young adults with MDD, there was no association between current depressive symptom severity and either HRV (RMSSD, R2 = 0.004, P = 0.73) or cardiac BRS (overall gain, R2 = 0.02, P = 0.85). Taken together, these data suggest that cardiac autonomic dysfunction may not contribute to elevated cardiovascular risk factor profiles in young unmedicated adults with MDD of mild-to-moderate severity.NEW & NOTEWORTHY This study investigated cardiac autonomic function in young unmedicated adults with major depressive disorder (MDD). The results demonstrated that both heart rate variability and cardiac baroreflex sensitivity were preserved in young unmedicated adults with MDD compared with healthy nondepressed young adults. Furthermore, in young adults with MDD, current depressive symptom severity was not associated with any indices of cardiac autonomic function.
Keywords: autonomic nervous system; cardiac baroreflex sensitivity; depression; heart rate variability.