Factors influencing cardiac vagal tone in depressed patients

Due to its close relationship to vagal tone, respiratory sinus arrhythmia is an attractive non-invasive indirect measure of peripheral parasympathetic activity. In the evaluation of respiratory sinus arrhythmia as a diagnostic or prognostic tool several influencing variables have yet to be considered. In this study we investigated a group of 122 healthy subjects and 46 patients suffering from major depression, melancholic type. 23 of them were drug-free and 23 received tricyclic antidepressants. In all subjects, chest-wall electrocardiograms were recorded during 5 minutes of rest in supine position. RR intervals and heart rate were obtained from the electrocardiograms. For the evaluation of cardiac vagal tone we took the logarithm of the median absolute heart rate differences between each heartbeat and the following (logRSA). According to our previous studies the simply to calculate logRSA highly correlates with the mathematically elaborate spectral estimation of cardiac vagal tone. We first studied the influence of age and sex on logRSA in the healthy subjects. Our results showed a significant linear decrease in logRSA with age and a tendency for higher values in women compared to men. In the second part of our study we found that 23 unmedicated depressed patients and their age- and sex-matched controls didnʹt have significantly different logRSA values compared to controls. In the third part of our study, anticholinergic treatment caused a significant decrease in logRSA without changing the age dependency observed in the other groups According to our results vagal tone decreases with age in healthy subjects as well as in depressed patients, independent of anticholinergic medication whereas the latter markedly reduces log-RSA values and hence cardiac vagal tone.