| Summary: | Many theoretical models addressing the role of the parasympathetic branch of the
autonomic nervous system in psychopathology predict decreased respiratory sinus
arrhythmia (RSA) in disorders such as depression and anxiety. However, decreased RSA
in depression is not consistently observed across studies. Research on the relationship
between anxiety and RSA has also been mixed, but the results may be more robust than
that of depression. Before the theoretical models can be re-examined based on these
findings, researchers must clarify the nature of these relationships. Specifically, three
things should be determined: a) is there a relationship between RSA and depression; b) is
there a relationship between anxiety and RSA; and c) could comorbid anxiety in
depression be playing a role in the mixed findings to date.
This study was specifically designed to address those three questions. Based on
the empirical literature, we hypothesized that: 1) depression would have a small but
significant relationship to RSA; 2) anxiety would have a significant relationship to RSA
that would be stronger than that of depression to RSA; 3) the anxiety-RSA relationship
would persist when controlling for depression, whereas the depression-RSA relationship
would not persist when controlling for anxiety. Additionally, the Cardiac Sympathetic
Index (CSI) was used to explore the potential relationships that depression and anxiety
may have with sympathetic-related heart rate variability and sympathovagal balance.
One-hundred and twenty-eight physically healthy undergraduate students
completed a questionnaire measure assessing depression and anxiety symptoms. Participants’ ECG recordings were taken both at rest and during a stressful arithmetic task
to obtain measures of RSA and CSI. Regression analysis revealed a significant inverse
relationship between anxiety and RSA, and a marginally significant inverse relationship
between depression and RSA, during the stressful arithmetic task. No significant
relationships were observed at rest, or with CSI. Importantly, the relationship between
anxiety and RSA persisted when controlling for depression, whereas the opposite was not
true: the relationship between depression and RSA is almost eliminated when controlling
for anxiety. These results suggest that some of the positive findings in the depression-
RSA literature may be due to uncontrolled, co-occurring anxiety symptoms.
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