Summating potential (SP) findings in Meniere's disease were reviewed based mainly on the results of our study. Many studies have confirmed that an increased negative SP is observed more often in ears with endolymphatic hydrops such as Meniere's disease than in ears with other diseases. Recent reports have showed that negative SP in Meniere's disease is unchanged during hearing fluctuation although action potential (AP) is changed, and that positive SP is more frequently observed in Meniere's disease. Our recent study suggests that positive SP may provide different information on the pathophysiology of Meniere's disease from that obtained from negative SP. Recent reports have demonstrated that the combination of electrocochleography with glycerol test increases the diagnostic rate of Meniere's disease.
Generally, the incidence of nystagmus decreases as the days from the onset of vertigo pass. To evaluate ENG findings accurately, we studied the relationship between the number of patients showing spontaneous and positional nystagmus on ENG and the number of days between onset and the recording day. Also, second recordings were obtained a few months after the first recordings. We reviewed four hundred and forty patients with vertigo and/or disequilibrium investigated by the Department of Otolaryngology of Joetsu General Hospital between 1990 and 1993. The following results were obtained. (1) In patients with peripheral vestibular disorders, the incidence of positional nystagmus within two weeks was higher than that more than two weeks after onset. On second recordings, the incidence decreased to half of that on the first recordings. (2) In patients with central disorders, there was no relationship between the incidence of positional nystagmus and the number of days after onset. We concluded that ENG recording should be carried out as early as possible following onset, especially in patients with peripheral vestibular disorders, and patients should be treated for a few months.
Long-term follow-up of patients with Meniere's disease was carried out with special regard to audiological change. Various kinds of audiograms were observed and audiological change differed in each patients. However, the most characteristic feature was fluctuating hearing impairment in lower frequencies. In aged patients and bilateral cases, audiogram was best understood by correcting the hearing level of affected ear by that in the non-affected ear or that of physiological hearing.
To evaluate dynamic postural control, the Body Tracking Test (BTT) was developed. This paper investigated the optical target speed. The subject standing on the stabilometer was asked to track a moving optical target displayed on the screen by his/her bodily movement. Stabilometric data were recorded and computer-analyzed. The horizontal or vertical span of the target was 15 cm. The optical target moved in a horizontal or vertical manner. The movement of the optical target was programmed by controlled triangular waves. The sampling time was 50 mseconds for a total of 60 seconds. The subject stood erect on the stabilometer with feet together and the display screen was placed at eye level. In the horizontal BTT, the gain for target and tracking was 1.8. In the vertical BTT, the gain for target and tracking was 1.6. Fifty healthy young adult volunteers (male 24, female 26) were tested. The mean age was 23.6 (19-34). They were examined in groups of five by target movement speed. We established the optical target speed at 0.025-0.4 Hz. Total distance of bodily movements was adjusted by body weight. To compare the results of each scale, the total distance of bodily movements was divided by total target movement. This ratio was named "Index of BTT movement". At 0.025 Hz, the index of BTT movement was at a maximum, while at 0.4 Hz, the index of BTT movement was almost 1.0. However at 0.4 Hz, the bodily movement became a fixed rhythmical movement. With a slow amplification such as 0.025 Hz, a larger adjustment was made accordingly amplification. Therefore, it was considered appropriate to use 0.125 Hz to obtain stable stabilometric data.
The effect of gentamicin on the cytoskeletal organization of guinea pig vestibular sensory cells. was investigated employing the saponin perfusion method and scanning electron microscopy. The intermediate filaments and microtubules were noted to have degenerated following gentamicin intoxication. Such degeneration was not linked to primary mitochondrial damage, but closely related to subsequent degeneration of Golgi apparatus and endoplasmic reticulum. These findings suggest that microtubules and intermediate filaments work closely together to maintain the structural integrity of both the Golgi apparatus and the membrane-bound organelles and that these can be altered by ototoxic drugs before degeneration of membrane-bound organelles occurs.
Although there were many previous reports related to saccadic eye movement in neurodegenerative disorders, discussions have been confined to maximal velocity and latency time, which are not sufficient to clarify abnormalities in all processes of the saccade. We, therefore, attempted to establish a new analytical method using a signal processor and personal computer, to monitor the whole process of a single saccade. This new method was used to study two groups, elderly normal controls and patients with Parkinson's disease (Hoehn-Yahr III), to categorize their saccade systems. The results were as follows; 1) In normal controls, the initial phase of saccadic eye movement was significantly shortened in elderly control compared to that in younger controls (p<0.01) and multistep saccade was increased in elderly persons. 2) In Parkinson's disease, shortness of the initial phase of saccadic eye movement, was much more accerelated by aging (p<0.01).
Active head turn with eyes closed may involuntarily induce transient saccadic eye deviation (TSD) in the direction of the head movement. This suspected of being provoked by activation of the lateral gaze center due to neck torsion. Using a computer, the maximal eye velocities of TSDs and visually elicited voluntary saccades of 20 degree were analyzed in 89 subjects aged 9 to 84. The mean velocity of TSD in subjects over 70 years of age was slower than that in the other age groups excluding the small number of subjects under age 20. In particular, a significant difference was noted between the elderly subjects and those in their 50s. Voluntary saccades, however, did not differ between age groups. In conclusion, age-related change in eye velocity was seen in involuntary TSD, but not in voluntary saccades. The velocity of TSD may be available for an assessment of aging.
To determine whether neurosteroids suggested to be present in the brain act on MVN neurons, we electrophysiologically examined the effects of pregnenolone sulfate (PS), a neurosteroid, on the neuronal activity of the medial vestibular nucleus (MVN) in cats anesthetized with α-chloralose. Single neuronal activity in the MVN was extracellularly recorded using a glass-insulated silver wire microelectrode attached to a sevenbarreled micropipette. Each micropipette was filled with PS (3 mM), monosodium glutamate (1 M), glutamic acid diethyl ester (GDEE 50 mM), or NaCI (3 mM). These chemicals were microiontophoretically applied to the immediate vicinity of the target neuron being recorded. The MVN neurons were classified as type I or II neurons according to their responses to horizontal and sinusoidal rotation. We examined the effects of the drugs on type I neurons. Microiontophoretically applied PS in doses of 50-200 nA dose-dependently increased spontaneous firing in 20 of 26 neurons examined; 6 neurons were not affected by drug doses up to 200 nA. Spontaneous firing did not decrease in any neurons. The PS-induced (100 nA) increase in spontaneous firing of MVN type I neurons was dose-dependently suppressed by the iontophoretic application of GDEE (50-200 nA), which also inhibited glutamate- and rotation-induced firing. These findings suggest that PS excites type I neurons through the glutamate receptor in MVN.
In patients with vertigo, complaints vary from a strong sensation of rotation to a vague feeling of unsteadiness. We investigated the relationship between vertiginous sensation and maximal slow phase velocity (SPV) of nystagmus during alternate bithermal caloric test in normal volunteers. We also studied age-related changes in the test results. The subjects consisted of 44 normal volunteers (10 males and 34 females), ranging from 17 to 78 (mean 43.9) years of age. Water stimuli of 40 ml at two different temperatures (30 and 44°C) were alternately given for 20 sec to the bilateral ears. Overall, 176 stimuli were administered. Results. Vertigo, dizziness and absence of abnormal feelings were noted in 79.8, 13.7 and 6.5% of all ear stimuli, respectively. Mean SPVs in subjects with these findings were 23.4, 15.8 and 16.7 °/sec, respectively. It was speculated that the sensation of rotation was accompanied by SPV above about 20°/sec. There were no significant differences of SPV between in subjects with dizziness and subjects without abnormal feelings. To study changes in vertiginous sensation and SPV with age, the subjects were divided into 5 groups with 10 year intervals. The mean SPVs accompanying vertiginous sensation were 25.4°/sec in the group <30 years, 20.5°/sec in the group ≥30 and <40 years, 24.6°/sec in the group ≥ 40 and < 50 years, 21.8°/sec in the group ≥50 and <60 years, and 24.8°/sec in the group ≥60 years. Since there were no significant differences among these groups, SPV accompanying vertiginous sensation did not correlate with age.
This study investigated the role of the foveal and peripheral visual fields in body sway control while standing upright. The subjects were 55 healthy adults. There were three visual conditions: presentation of a fixation point (foveal visual information) with cross-shaped vertical and horizontal lines stretching to the limits of the subject's viewing range (peripheral visual information), called the FP-condition; presentation of a fixation point only (F-condition); and the absence of visual information with the subject's eyes shut (N-condition). Three types (lateral, fore-aft, and total) of magnitude of body sway (MBS) were calculated. (1) For both total and fore-aft body sways, the MBS of the N-condition was significantly larger than those of other conditions. The MBS of the FP-condition was nearly equal to that of the F-condition. (2) For lateral body sway, the MBS of the N-condition was significantly larger than those of other conditions. The MBS of the F-condition was significantly larger than that of the FP-condition.
Prospective follow-up study was performed on 41 patients presenting with spontaneous vertigo attack between June 1991 and May 1995. The final diagnoses consisted of 24 vertiginous diseases (unknown cause), 9 vertebro-basilar insufficiency, one multiple cerebral infarction, 3 cerebellar infarction, one cerebellar hemorrhage, 2 vestibular neuritis and one Menieres disease. Investigation of cases presenting with vertigo of shorter duration ranging from seconds to hours suggested that central circulatory disorder was the most important among causes inducing spontaneous transient vertigo at-tack. Severe balance disorder observed even with the patient's eyes open seemed to be a critical finding suggesting cerebellar vascular disorders.
Position perception during linear movement was estimated quantitatively using a joystick device with and without visual information (VI). Eight healthy male subjects (19-24 years old) seated inside a capsule mounted on a linear accelerator were subjected to a constant g-load of 0.02 g along the X (antero-posterior) axis with varying displacement of 4 m, 10 m, 16 m, and to a constant displacement of 10 m with varying g-load of 0.02 g, 0.05 g and 0.08 g. The subjects were given the instruction to tilt a joystick in proportion to distance from starting position to present position during linear movement. The subject's position perception fitted Stevens' power law (R=kSn, R is output of joystick, k is a constant, S is displacement of linear movement, n is an exponent). The mean exponent was 0.49 for backward movement and 0.50 for forward movement without VI, and 0.80 for backward movement and 0.83 for forward movement with VI. Between backward and forward movements, there was no significant difference (p>0.1, paired t-test) of exponents and there was a correlation (r=0.90, p<0.01) of exponents under both visual conditions. Comparing absence of VI and VI, there was a significant difference (backward: p<0.002, forward: p<0.004, paired t-test) in exponents and no correlation of exponents (r=0.03, p>0.1). The position perception of 10 m displacement was not influenced by linear acceleration (0.02 g-0.08 g). We concluded that the method used in this study was useful for quantitative estimation of self-motion perception and could partly clarify properties of position perception for linear movement along the X axis.
It is well known that some kinds of vertigo or hearing disturbances are caused by impairment of vertebro-basilar circulation. It is important to determine whether unilateral vertebral artery (VA) occlusion causes an imbalance between bilateral inner ear blood flow. In this study, we investigated the influence of unilateral VA occlusion and hypotension on bilateral inner ear blood flow in rats. Using the microsphere surface methods, we measured blood flow of the cochlea and three semicircular ampullae. In control animals, the differences between blood flow in the right and left cochleae and semicircular ampullae were not significant. In animals with VA occlusion and hypotension, the differences were not significant either. In addition to these findings, we discuss the possibility of imbalance between bilateral inner ear blood flows caused by VA occlusion with consideration of previous reports.