Effects of low-dose transdermal scopolamine on autonomic cardiovascular control in healthy young subjects

We studied how posture influences the effects of transdermal scopolamine on autonomic cardiovascular regulation in a randomized, double-blind, placebo-controlled crossover study of 10 healthy young volunteers. We recorded the electrocardiogram and auscultatory sphygmomanometric and continuous non-invasive finger arterial pressure (Finapres device) to obtain signals for the beat-by-beat R-R interval and systolic, mean and diastolic pressures. R-R interval and arterial pressure variabilities were characterized by power spectral analysis. Scopolamine increased the mean R-R intervals and reduced arterial pressure in both the supine and the standing positions, but did not affect blood pressure variability. Scopolamine increased the total variability of R-R interval and its mid- (0.07-0.15 Hz) and high- (0.15-0.40 Hz) frequency band power in the standing position during controlled breathing at 0.25 Hz. In the supine position, scopolamine did not affect R-R interval variability. In the deep breathing test, scopolamine increased the maximal expiratory-inspiratory R-R interval ratio. This study showed that low-dose scopolamine increases vagal cardiac inhibition in both supine and standing positions in healthy volunteers. However, scopolamine increases heart rate variability only in the standing position during partial vagal withdrawal. The study also demonstrates that transdermal scopolamine decreases blood pressure in healthy young subjects.