Autonomic laterality in caloric vestibular stimulation

Area of Science:

• Neuroscience
• Otolaryngology
• Autonomic Nervous System Physiology

Background:

• Caloric stimulation of the vestibular system is known to elicit autonomic responses.
• Lateralization of nervous system activity influences autonomic nervous system function.

Purpose of the Study:

• To investigate and compare the effects of right versus left ear caloric vestibular stimulation on cardiac sympathovagal tone in healthy subjects.
• To assess changes in heart rate variability (HRV) as an indicator of sympathovagal balance.

Main Methods:

• A self-controlled study involving 12 healthy male volunteers.
• Minimal ice water caloric test (1 mL at 4±2°C for 1s) applied to one ear at a time.
• Comparison between optimum (horizontal semicircular canal stimulation) and pessimum (sham control) head positions.
• Short-term heart rate variability (HRV) analysis for cardiac sympathovagal tone metrics.
• Analysis of variance (ANOVA) used for statistical comparisons.

Main Results:

• Caloric vestibular stimulation did not produce significant changes in short-term time-domain and frequency-domain HRV indices.
• Systolic and diastolic arterial blood pressure, respiratory rate, and amplitude also showed no significant alterations.
• Nystagmus duration differed significantly between optimum and pessimum positions for both left and right ear stimulations.
• No significant differences in the onset time of nystagmus were observed between sides or positions.

Conclusions:

• Minimal ice water caloric stimulation of either the right or left vestibular system does not impact cardiac sympathovagal balance in healthy individuals.
• HRV indices serve as reliable indicators for assessing sympathovagal tone changes during caloric vestibular testing.