Coefficient variation of R-R intervals during caloric vestibular stimulation

We applied a new system that estimates autonomic nerve function during severe nausea arising during caloric vestibular stimulation. We monitored electrocardiograms of twenty-six healthy volunteers and four patients during caloric vestibular stimulation. Nine people were stimulated with 6 liters/min of 37°C and 24°C air into each ear at random. Twenty-one people were stimulated with the same amount of air but in the following order: right ear, 24°C; left ear, 24°C; right ear, 50°C; and left ear, 50°C. After caloric vestibular stimulation, eleven people developed severe nausea and they were defined as the severe group. The others were put into the mild group. The coefficient of variation of the 50 R-R intervals (CV) was analyzed by a personal computer in order to be aware of any small changes in autonomic function. No significant change of CV was seen between 24°C and 37°C stimulation. In the mild group, 50°C stimulation resulted in decreased CV, but in the severe group, there was increased CV with 50°C stimulation. A high CV was associated with severe nausea. In conclusion, nausea in caloric vestibular stimulation was associated with increased parasympathetic nervous system activity.