Exploring the biomechanical responses of human cupula by numerical analysis of temperature experiments

The vestibular receptor of cupula acts an important role in maintaining body balance. However, the cupula buried in the semicircular canals (SCCs) will be destroyed if it is detached from the relevant environment. The mechanical properties of human cupula still remain ambiguous. In this paper, we explored the cupula responses changing with temperature by experiments and numerical simulation of SCCs model. We obtained 3 volunteers’ nystagmus induced by constant angular acceleration when the temperature of volunteers’ SCCs was 36 °C and 37 °C respectively. The slow-phase velocity of 3 volunteers decreased by approximately 3°/s when the temperature of SCCs reduced by 1 °C, which corresponded to the reduction of cupula deformation by 0.3–0.8 μm in the numerical model. Furthermore, we investigated the effects of the variation of endolymphatic properties induced by temperature reduction on cupula deformation through numerical simulation. We found that the decrease of cupula deformation was not caused by the change of endolymphatic properties, but probably by the increase of cupula’s elastic modulus. With the temperature reducing by 1 °C, the cupula’s elastic modulus may increase by 6–20%, suggesting that the stiffness of cupula is enhanced. This exploration of temperature characteristic of human cupula promotes the research of alleviating vestibular diseases.

Exploring the Mechanical Properties of Human Cupula by Numerical Analysis of Temperature Experiments

The vestibular receptor of cupula acts an important role in maintaining body balance. However, the cupula buried in the semicircular canals (SCCs) will be destroyed if it is detached from the relevant environment. The mechanical properties of human cupula still remain ambiguous. In this paper, we explored the cupula’s elastic modulus changing with temperature by experiments and numerical simulation of SCCs model. We obtained 3 volunteers’ nystagmus induced by constant angular acceleration when the temperature of volunteers’ SCCs was 36℃ and 37℃ respectively. The slow-phase velocity of 3 volunteers decreased by approximately 3°/s when the temperature of SCCs reduced by 1℃, which corresponded to the reduction of cupula deformation by 0.3–0.8 µm in the numerical model. Furthermore, we investigated the effects of the variation of endolymphatic properties induced by temperature reduction on cupula deformation through numerical simulation. We found that the decrease of cupula deformation was not caused by the change of endolymphatic properties, but probably by the increase of cupula’s elastic modulus. With the temperature reducing by 1℃, the cupula’s elastic modulus may increase by 6%-20%, suggesting that the stiffness of cupula is enhanced. This exploration of temperature characteristic of human cupula promotes the research of alleviating vestibular diseases.

Alexander's Law During High-Speed, Yaw-Axis Rotation: Adaptation or Saturation?

Objective: Alexander's law (AL) states the intensity of nystagmus increases when gaze is toward the direction of the quick phase. What might be its cause? A gaze-holding neural integrator (NI) that becomes imperfect as the result of an adaptive process, or saturation in the discharge of neurons in the vestibular nuclei?Methods: We induced nystagmus in normal subjects using a rapid chair acceleration around the yaw (vertical) axis to a constant velocity of 200°/second [s] and then, 90 s later, a sudden stop to induce post-rotatory nystagmus (PRN). Subjects alternated gaze every 2 s between flashing LEDs (right/left or up/down). We calculated the change in slow-phase velocity (ΔSPV) between right and left gaze when the lateral semicircular canals (SCC) were primarily stimulated (head upright) or, with the head tilted to the side, stimulating the vertical and lateral SCC together.Results: During PRN AL occurred for horizontal eye movements with the head upright and for both horizontal and vertical components of eye movements with the head tilted. AL was apparent within just a few seconds of the chair stopping when peak SPV of PRN was reached. When slow-phase velocity of PRN faded into the range of 6–18°/s AL could no longer be demonstrated.Conclusions: Our results support the idea that AL is produced by asymmetrical responses within the vestibular nuclei impairing the NI, and not by an adaptive response that develops over time. AL was related to the predicted plane of eye rotations in the orbit based on the pattern of SCC activation.

Ictal downbeat nystagmus in Ménière disease

ObjectiveTo determine the mechanism of ictal downbeat nystagmus in Ménière disease (MD), we compared the head impulse gain of the vestibulo-ocular reflex (VOR) for each semicircular canal between patients with (n = 7) and without (n = 70) downbeat nystagmus during attacks of MD.MethodsWe retrospectively analyzed the results of video-oculography, video head-impulse tests, and cervical vestibular-evoked myogenic potentials (VEMPs) in 77 patients with definite MD who were evaluated during an attack.ResultsPure or predominant downbeat nystagmus was observed in 7 patients (9%) with unilateral MD during the attacks. All 7 patients showed spontaneous downbeat nystagmus without visual fixation with a slow phase velocity ranging from 1.5 to 11.2°/s (median 5.4, interquartile range 3.7–8.5). All showed a transient decrease of the head impulse VOR gains for the posterior canals (PCs) in both ears (n = 4) or in the affected ear (n = 3). Cervical VEMPs were decreased in the affected (n = 2) or both ears (n = 2) when evaluated during the attacks. Downbeat nystagmus disappeared along with normalization of the VOR gains for PCs after the attacks in all patients. During the attacks, the head impulse VOR gains for the PC on the affected side were lower in the patients with ictal downbeat nystagmus than in those without (Mann-Whitney U test, p < 0.001), while the gains for other semicircular canals did not differ between the groups.ConclusionDownbeat nystagmus may be observed during attacks of MD due to an asymmetry in the vertical VOR or saccular dysfunction. MD should be considered in recurrent audiovestibulopathy and ictal downbeat nystagmus.

Vestibular Function and Motion Sickness Susceptibility: Videonystagmographic Evidence From Oculomotor and Caloric Tests

Purpose Motion sickness (MS) is a common condition that affects millions of individuals. Although the condition is common and can be debilitating, little research has focused on the vestibular function associated with susceptibility to MS. One causal theory of MS is an asymmetry of vestibular function within or between ears. The purposes of this study, therefore, were (a) to determine if the vestibular system (oculomotor and caloric tests) in videonystagmography (VNG) is associated with susceptibility to MS and (b) to determine if these tests support the theory of an asymmetry between ears associated with MS susceptibility. Method VNG was used to measure oculomotor and caloric responses. Fifty young adults were recruited; 50 completed the oculomotor tests, and 31 completed the four caloric irrigations. MS susceptibility was evaluated with the Motion Sickness Susceptibility Questionnaire–Short Form; in this study, percent susceptibility ranged from 0% to 100% in the participants. Participants were divided into three susceptibility groups (Low, Mid, and High). Repeated-measures analyses of variance and pairwise comparisons determined significance among the groups on the VNG test results. Results Oculomotor test results revealed no significant differences among the MS susceptibility groups. Caloric stimuli elicited responses that were correlated positively with susceptibility to MS. Slow-phase velocity was slowest in the Low MS group compared to the Mid and High groups. There was no significant asymmetry between ears in any of the groups. Conclusions MS susceptibility was significantly and positively correlated with caloric slow-phase velocity. Although asymmetries between ears are purported to be associated with MS, asymmetries were not evident. Susceptibility to MS may contribute to interindividual variability of caloric responses within the normal range.

Static Positional Nystagmus in the Healthy Vestibular System

A repeat of the seminal 1973 study on static positional nystagmus (PN) using more accurate recording techniques.The purpose was to further characterize PN and, using current data, introduce new clinical criteria for its identification.Static PN was recorded in ten positions with vision denied. Each position was analyzed using age, gender, presence, direction, and persistence of nystagmus while taking into account the number of beats and mean slow-phase velocity (SPV).One hundred healthy patients who were asymptomatic with no known neurological disorders were tested.No intervention was used.Analysis of variance, descriptive statistics, and confidence intervals were used to describe results.Results showed 74% of normal participants had horizontal nystagmus in at least one position. Only 7% of the observed nystagmus was persistent. The average SPV was 2°/sec. The mean number of positions in which nystagmus was observed was three. Neither age nor gender influenced the occurrence of nystagmus. Forty-three percent of the participants had vertical nystagmus in at least one position; however, the SPV was 2°/sec or less.The present study demonstrated that intermittent or persistent PN in four or fewer positions should not be considered pathological when the SPV is 4°/sec or less (n = 100). Observance of vertical nystagmus in one position should not be considered pathological if the SPV is 2°/sec or less. Suggested positions for positional testing should include seated-upright, supine, head right, head left, head-hanging, and the precaloric (30° supine) positions. Fixation when PN is observed is indicated.

Comparing mastoid and posterior cervical muscles vibration effects on eye movement in normal subjects

Background and Aim: Vibration is a method for stimulating the vestibular system. This met­hod can unmask asymmetry between two vesti­bular systems (such as unilateral peripheral ves­tibular disorders). The occurrence of vibration-induced nystagmus (VIN) in healthy subjects can affect the diagnosis of patients with uni­lateral peripheral vestibular disorders. Thus, the evaluation of VIN in healthy subjects is critical to help the diagnosis of unilateral peripheral vestibular disorders. Methods: This study was carried out on 72 hea­lthy subjects (mean ± SD age: 27.12 ± 4.97 years) in the Auditory and Balance Clinic of Rofeideh Rehabilitation Hospital. Vibration sti­mulation with a frequency of 30 and 100 Hz was used on mastoid and posterior cervical mus­cles (PCMs) and simultaneously eye movements were recorded and analyzed using videonystag­mography. Results: The mastoid vibration with a frequ­ency of 30 and 100 Hz, respectively produced VIN in 16.67% and 27.78% of subjects and VIN observed in PCMs vibration with a frequency of 30 and 100 Hz in 4.17% and 9.72% of the subjects. Conclusion: The occurrence of VIN in healthy subjects was more probable with mastoid vib­ration in 100 Hz. In this study, VIN was pre­dominantly horizontal, its direction was toward the stimulated side, and its slow phase velocity was lower than 5 deg/s. These criteria could be used for differentiation between normal and abnormal subjects.

Optokinetic Analysis in Patients With Spontaneous Horizontal Gaze-Evoked Nystagmus Without Radiological Neuropathology

Gaze-evoked nystagmus is not rare among those who have acute balance problem and may indicate a cerebellar dysfunction that is associated with a broad spectrum of disorders. The aim of this study is to analyze optokinetic response in those patients. Eleven males and 7 females (age range: 25-60, 42.5 [9.75]) with gaze-evoked nystagmus were analyzed with optokinetic test (Micromed Inc). Nystagmus was elicited by a stimulator light spot moving across the patient’s visual field at a target speed of 30 degree/second. Ten age-matched healthy participants served as controls. The gain and slow-phase velocity difference in oculomotor response from left and right stimulus was compared in patients and the control participants. One-way analysis of variance test was used for multiple variance analysis of the groups. Statistical significance was set at P < .05. Slow-phase velocity of gaze-evoked nystagmus was ranging between 6 and 19 degree/second. The mean slow-phase velocity of gaze-evoked nystagmus to the right and left was 8.1 (3.81) and 6.8 (4.67) degree/second, respectively. Optokinetic gain was out of normal limits in 10 (55.5%) patients. Comparison of mean gain difference between the patients and the normal participants was statistically significant ( P = .025). No statistical difference was found in mean slow-phase velocity difference in optokinetic nystagmus between control participants and patients ( P > .05 [.099]). An acute-onset balance problem may be associated with dysfunction of separate populations of neurons in the brainstem and cerebellum even if there is no radiological neuropathy since gaze-evoked nystagmus is a sign of neural integrator dysfunction. Patients with gaze-evoked nystagmus and optokinetic abnormalities may have disruption of cerebellar pathways and should be followed closely.

Comparison of Vestibular Function Between Right and Left Handed Normal Population

Objective To identify the side of vestibular dominance in right handed & left handed people. Method A total of 50 normal subjects, aged between 15 - 45 years were included as Left handers (n = 25) and Right handers (n = 25). Handedness was confirmed by the Annett Hand Preference Questionnaire. Bithermal caloric testing was done which was recorded by Electronystagmography (ENG). Maximum Slow Phase Velocity (MSPV) was taken as the parameter of choice. Directional Preponderance (DP) and Canal Paresis (CP) were calculated in each group. Results Out of the 25 Left handed subjects, 8 had DP towards Left whereas 7 had DP towards the Right and the remaining 10 showed no DP to any side (normal) (p<0.001). Out of the 25 Right handed subjects, 4 had DP towards Right and none had DP towards the Left, remaining 21 showed no DP to any side (normal) (p<0.001). For CP, out of 25 Left handed subjects, 2 showed CP towards the Left and 1 towards the Right, the remaining 22 showed no CP (normal) at all. Similarly out of the 25 Right handed subjects, 2 showed CP towards the Left and 1 towards the Right, the remaining 22 showed no CP (normal) at all. Out of 25 Right handers, it was found that Right handers showed Right vestibular preference whereas vestibular preference was almost equally distributed to Left and Right side in Left handers. Conclusion On considering DP, it was found that Right handers showed Right vestibular preference whereas vestibular preference was almost equally distributed toLeft and Right side in Left handers (p<0.001).