Comparative study of caloric responses induced by different stimulus intensities

Area of Science:

• Vestibular System Physiology
• Neuroscience
• Ophthalmology

Background:

• Bithermal caloric testing is a standard method for assessing vestibular function.
• Understanding the distribution patterns of nystagmus parameters is crucial for accurate interpretation.
• Previous studies have not fully characterized the distribution of caloric responses across different stimulus intensities.

Purpose of the Study:

• To compare bithermal caloric responses using varying water volumes (20, 50, 240 ml) in healthy adults.
• To analyze the distribution patterns of nystagmus parameters (SPEV, duration, frequency) under different stimulus conditions.
• To determine the optimal stimulus volume for linear distribution and reliable normal range calculation.

Main Methods:

• 111 healthy Japanese adults underwent bithermal caloric testing with 20, 50, and 240 ml irrigations.
• Maximal slow-phase eye velocity (SPEV), duration, and maximal frequency of nystagmus were recorded.
• Distribution patterns were analyzed using regular and logarithmic scales, including probit plots.

Main Results:

• Nystagmus parameters showed normal distribution on a logarithmic scale but not a regular scale.
• The 240 ml caloric test demonstrated the most linear distribution across all three parameters in probit plots.
• The normal range (mean ± 2 SD) was consistently wider with larger volumes, while the range width showed minimal change.

Conclusions:

• A 240 ml water volume provides the most linear and consistent distribution for caloric nystagmus parameters.
• Logarithmic scaling is more appropriate for analyzing caloric response distributions than regular scaling.
• Findings support the use of larger stimulus volumes for more reliable assessment of vestibular function and normal range determination.