The influence of major depression and its treatment on heart rate variability and pupillary light reflex parameters

Background: The link between depression and autonomic dysfunction has attracted more attention since epidemiological studies have revealed that depressed patients have an augmented risk of cardiovascular morbidity and mortality. Former studies of autonomic dysfunction in major depression have shown inconclusive results. Aims: To further elucidate the effect of depression and medication on autonomic function, 18 patients and 18 matched control subjects were comprehensively assessed once medicated and once non-medicated as well as after full clinical recovery. Methods: Cardiac autonomic function was evaluated by measuring heart rate variability (HRV) parameters, and central autonomic tone was investigated by obtaining parameters of the pupillary light reflex (PLR). Results: Acutely depressed patients who had not taken antidepressant medication for 8 weeks prior to the investigation differed significantly neither in heart rate parameters nor in parameters of the PLR from their controls. However, after 2 days of antidepressant treatment (SSRI and NaSSRI), parameters of heart rate analysis and PLR (except relative amplitude) changed significantly and remained significantly different after clinical recovery. Limitations: The study needs to be repeated using larger patient groups. Long-term studies are absolutely essential. Conclusion: The state of depression did not influence autonomic parameters significantly. In fact, treatment influenced autonomic function far more than the disease itself. Other branches of the autonomic nervous system (ANS), as well as new techniques should be applied to elucidate whether small changes in autonomic function exist. This might clarify whether disease or treatment might influence cardiac mortality in depression.