Abstract
BACKGROUND: The aim of this study was to identify the aspects of cardiac physiology associated with depressive disorder early in life by examining measures of autonomic cardiac control in a community-based sample of depressed adolescents at an early phase of illness, and matched on a number of demographic factors with a nondepressed comparison group. METHODS: Participants were 127 adolescents (44 boys), ages 14-18, who formed two demographically matched groups of clinically depressed and nondepressed participants. Adolescents were excluded if they evidenced comorbid externalizing or substance-dependence disorders, were taking medications with known cardiac effects, or reported regular nicotine use. Resting measures of heart rate, respiratory sinus arrhythmia, skin conductance level, blood pressure, and pre-ejection period were collected. RESULTS: Depressed adolescents had resting heart rates significantly higher than those of healthy adolescents. No other measure of autonomic functioning differentiated the groups. Post hoc analyses were conducted to examine the influence of illness chronicity, severity, comorbidity, and sex on cardiac psychophysiology. These variables did not appear to exert a significant influence on the findings. CONCLUSIONS: Our findings suggest that neither autonomic cardiac control, illness chronicity, or severity, nor medication effects fully explain resting heart rate differences between depressed and nondepressed adolescents. Future research on depression and heart rate should consider mechanisms other than sympathetic or parasympathetic control as potential explanations of heart rate differences, including blood-clotting mechanisms, vascular and endothelial dysfunction of the coronary arteries, and inflammatory immune system response.