Autonomic effects on R-R variations of the heart rate in the squirrel monkey: an indicator of autonomic imbalance in conflict sickness.

To assess the contribution of the autonomic nervous system (ANS) to beat-to-beat (R-R interval) variations in the squirrel monkey, heart rate was analyzed after atropine, propranolol, carbachol, or isoproterenol administration, using a computer analyzing system. Heart rate variations were expressed as coefficient of variance (CV) of mean R-R interval. CV of R-R interval clearly was reduced by atropine but not by propranolol, indicating that the effect could be mediated through the parasympathetic nerve. CV of R-R interval was measured also under vestibulo-visual conflict (VVC) situation in pitch. Although CV of R-R interval increased during VVC, this variation almost was abolished after atropine administration. Monkeys with unilateral labyrinthectomy showed smaller variations than those without operation during exposure to VVC. CV of R-R interval is a useful parameter for the objective and quantitative evaluation of ANS function and may be a good indicator to demonstrate the severity of motion sickness without invasive methods.