Three-dimensional analysis of post-caloric nystagmus caused by postural change

Three-dimensional characteristics of nystagmus induced by low frequency in semicircular canals of healthy young people

Objective

The study aimed to analyze the three-dimensional characteristics of nystagmus induced by different semicircular canal combinations in healthy young people, and to determine the reference range of nystagmus slow phase velocity (SPV) and its asymmetry.

Materials and methods

Fifty-two healthy volunteers (26 males and 26 females, aged 17-42 years, average 23.52 ± 6.59), were recruited to perform the manual triaxial rotation testing with a 3D-Videonystagmography (3D-VNG) device (VertiGoggles (ZT-VNG-II), Shanghai ZEHNIT Medical Technology Co., Ltd., Shanghai, China) using a 0.3 Hz prompt beat and a 90° amplitude, respectively. The induced nystagmus around the Z-, X-, and Y-axes were recorded in the yaw, pitch, and roll planes. The directions and slow phase velocities of the horizontal, vertical, and torsional components of the induced nystagmus under different semicircular canal combinations (the left lateral and right lateral semicircular canal combination, bilateral anterior semicircular canals, bilateral posterior semicircular canals combination, and the anterior and posterior semicircular canals combination of each ear), as well as their asymmetry, were taken as the observation indexes to analyze the characteristics of the nystagmus vectors of different combinations.

Results

Fifty-two healthy volunteers had no spontaneous nystagmus. The characteristic nystagmus was induced by the same head movement direction in all three axial rotation tests. The SPVs of the left and right nystagmus were 44.45 ± 15.75°/s and 43.79 ± 5.42°/s, respectively, when the subjects' heads were turned left or right around the Z-axis (yaw). The SPVs of vertically upward and downward nystagmus were 31.67 ± 9.46°/s and 30.01 ± 9.20°/s, respectively, when the subjects' heads were pitched around the X-axis (pitch). The SPVs of torsional nystagmus, with the upper poles of the eyes twisting slowly to the right and left ears (from the participant's perspective), were 28.99 ± 9.20°/s and 28.35 ± 8.17°/s, respectively, when the subjects' heads were turned left or right around the Y-axis (roll). There was no significant difference in the SPVs of nystagmus induced by the same rotation axis in two opposite directions (p > 0.05). The reference ranges for the slow phase velocities (SPVs) of nystagmus induced by the triaxial rotation testing were as follows: For the Z-axis (yaw), the SPVs were 13.58-75.32°/s for leftward head rotation and 13.56-74.02°/s for rightward head rotation. For the X-axis (pitch), the SPVs were 13.13-50.21°/s for upward head nystagmus and 11.98-48.04°/s for downward head nystagmus. For the Y-axis (roll), the SPVs were 10.97-47.02°/s for the left-sided head rotation and 12.34-44.35°/s for the right-sided head rotation.

Conclusion

This study clarified the three-dimensional characteristics of nystagmus induced by different semicircular canal combinations in healthy young people. It also established a preliminary reference range of SPVs and SPV asymmetry of nystagmus induced by the vertical semicircular canal. It can further provide a basis for the mechanism of semicircular canal-induced nystagmus and the traceability of nystagmus in patients with otogenic vertigo. It is shown that the portable 3D-VNG eye mask can be used for the manual triaxial rotation testing to achieve the evaluation of the low-frequency angular vestibulo-ocular reflex (aVOR) function of the vertical semicircular canal, which is convenient, efficient, and practical.

Age-related hearing changes and effects of exotoxin on inner ear function in aging rat. A frequency-specific auditory brainstem response study

Frequency-specific auditory brainstem responses to tone bursts (2-31.5 kHz) and tuning curves were recorded in 8 male rats during their entire life. No significant threshold elevation occurred during the 1st year. Mean age at onset of hearing loss was 20 months, with individual variations ranging from 14 up to 23 months. In most animals, threshold elevations were limited to 20 and 31.5 kHz. At age of 18-23 months, 3 rats were treated with Pseudomonas aeruginosa exotoxin A. After instillation, threshold elevation occurred at all frequencies, followed by near-total recovery at low frequencies, but only partial reversibility at high frequencies. It is concluded that aging-related hearing changes in Sprague-Dawley albino rats start at different ages, particularly comprising high frequencies and encroaching on the middle and low areas with increasing age.

Interleukin-2 affects cochlear function gradually but reversibly

Interleukin-2 (IL-2), one of the chemical mediators produced by helper T cells, activates its target cells via its receptor and induces inflammatory reactions indirectly. In this study, IL-2 was instilled into the round window niche of rats and the electrophysiological effects of inflammation on the inner ear were evaluated by a frequency-specific auditory brainstem response (ABR) technique. ABR threshold curves and intensity-latency (I-L) curves were investigated. In most cases, moderate sensorineural hearing loss (SNHL) was observed in the high-frequency areas (16-31.5 kHz). In the time course investigation of I-L curves, the responses of SNHL type appeared only 1 day after instillation (day 1) gradually becoming more prominent, to become most pronounced on days 5-7. The electrophysiological impairment was reversible within 2 weeks. Differing degrees of responsiveness of effusion production were observed following the instillation of IL-2, varying from pronounced middle ear effusion causing rather severe mixed hearing loss, to complete lack of effusion. Inflammation induced by IL-2 affects cochlear function gradually but reversibly.