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In a previous report (1) the author described a new air caloric test with continuous thermal change. In this study, 19 patients with vestibular disorders were examined with this technique, and the results were compared with the results of the water caloric test (30 degrees C, 50 ml, 20 s) in the same subjects. A difference in interaural response to the air caloric test was noted in 9 of the 19 patients (47.4%), greater than with the water caloric test, 5 of 19 (26.3%). The detectability of vestibular disorders with the air caloric test (28 of 38 ears; 73.7%) was significantly higher than that with the water caloric test (8 of 38 ears; 21.1%) (p0.01). The air test appeared to estimate vestibular function more precisely, as stimulation by this method is too weak to cause vestibular recruitment.

From 1975 to 1990, nationwide surveys on Menière's disease were performed three times by the Research Committee of Menière's disease (1975-76) and the Research Committee of Peripheral Vestibular Disorders (1982-84 and 1990) in Japan. Nine hundred and fifty-eight definite Menière cases, 520 in the 1st, 230 in the 2nd and 148 in the 3rd survey, were sampled by the members of the Committees. The epidemiological and clinical characteristics of Menière's disease were analyzed and compared with such control cases as other vertiginous patients, ENT patients without vertigo, and healthy subjects. In Menière's disease, the male to female ratio has changed from even to female predominance over the 15 years the study ran. The age distribution at onset peaked in the forties for males and thirties for females. Significant epidemiological results are summarized as follows: Definite Menière's disease has a higher incidence in married persons and in people with a nervous and precise character, whereas the incidence is lower in obese people. Physical and mental fatigue induced the onset of attacks. Menière's disease happened in day time in many cases, especially during the afternoon. As these epidemiological findings were commonly observed in all the surveys, the results are considered to be universal epidemiological characteristics of Menière's disease in Japan. In the same period, regional investigations were performed by Toyama Medical Association and our University. The male to female ratio in Toyama indicated a more significant female predominance than in the nationwide surveys. The prevalence of Menière's disease in Toyama Prefecture has been almost constant in all surveys, about 17/100,000 since 1974.(ABSTRACT TRUNCATED AT 250 WORDS)

For neurotological research we designed a soundproof pressure chamber in which pressure can be adjusted +/- 1000 mmH2O at the rate of less than 100 mmH2O per second. Noise in the chamber can be maintained under 30-35 dB while pressure is kept at a given level.

We correlated the surgical findings and the findings of computerized tomographic scans of the temporal bone in 38 ears from 38 patients with Menière's disease (31 unilateral and 7 bilateral) treated by endolymphatic sac (ES) drainage surgery between 1986 and 1991. At surgery, the position and size of the ES were recorded. The position of the ES was classified as one of three types according to Arenberg's parameters (type I, type II and type III) and the size of the ES was classified as large, intermediate or small. Scans encompassing the lateral semicircular canal were used to measure the minimum distance between the posterior semicircular canal and the posterior petrous surface (P-P distance). The P-P distance in 23 type III cases was significantly shorter (2.25 mm) than in 13 type II cases (3.39 mm). The P-P distance in 9 large-sized ES cases was significantly longer (3.99 mm) than in 20 intermediate-sized ES cases (2.40 mm) and in 9 small-sized ES cases (1.92 mm). Significant correlations were found in patients with Menière's disease between a short P-P distance and type III ES position, and also between a short P-P distance and an intermediate or small-sized ES.

High resolution transverse axial computerized tomograph (CT) encompassing the lateral semicircular canal (LSC) was used to measure the size of the petrous bone in ears with bilateral (n = 13) and unilateral (n = 38) Menière's disease, and in ears with unilateral chronic otitis media (n = 25) as a control group. Measurements were made of the following 4 distances in the petrous bone; A: the distance between the posterior semicircular canal (PSC) and the posterior petrous surface (PPS) (P-P distance), B: the distance between the PSC and the LSC (P-L distance), C: the distance between the vestibule and the PPS (V-P distance), and D: the distance between the PSC and the anterior margin of the sigmoid sinus (P-S distance). The P-P and the V-P distances were significantly shorter in ears with Menière's disease, especially in ears with bilateral Menière's disease compared to the nonaffected ears in unilateral Menière's disease or ears with chronic otitis media. This tendency was clearer in the P-P distance than in the V-P distance. The P-L and P-S distances did not show any statistical difference between groups. The results indicate that bone development between the PSC and the PPS and between the vestibule and the PPS, which usually contains the endolymphatic duct and sac, is significantly poorer in ears with Menière's disease than in ears with chronic otitis media. Hypoplasia of the retrolabyrinthine region may be an important factor in the pathogenesis of endolymphatic hydrops.

A new technique was designed for vestibular testing with an air caloric stimulator. With this technique, the temperature threshold necessary to induce caloric nystagmus was measured as air temperature decreased at a constant rate (from 37 degrees C). As a pilot study, an air caloric test with continuous thermal change was done at 6 different rates of decrease: 0.01, 0.03, 0.05, 0.1, 0.15 and 0.2 degrees C/s. The rate of 0.05 degrees C/s gave the smallest standard deviation for temperature threshold in normal subjects. This deviation had the narrowest normal limits of all ordinary caloric tests when the coefficient of variation was compared (standard deviation/mean x 100). No discomfort was observed during or after the air caloric test with continuous thermal change at this rate.

Hearing is assumed to be altered during or immediately after a change in atmospheric pressure, although this has not been tested experimentally. We used a soundproof pressure chamber to examine the effect of alterations in atmospheric pressure on hearing in 26 normal healthy subjects. The subjects were placed in the soundproof pressure chamber in a supine position and instructed to actively equilibrate middle ear pressure or to abstain from doing so. When the pressure was changed to +/- 500 mmH2O at 33 mmH2O/s the results were as follows: When subjects did not equilibrate middle ear pressure, air conduction at low frequency tones increased more than bone conduction. The degree of deterioration in hearing was greater when the chamber pressure was increased (descent) than where pressure was decreased (ascent). When the subjects equilibrated middle ear pressure, little change in the levels of air or bone conduction was observed. Most of the deterioration in bone conduction was considered to reflect functional loss due to increased stiffness and damping of the sound transmission mechanism.

A swimming test was used to evaluate vestibular function in guinea pigs. We first observed tracings of the swimming patterns of 20 healthy guinea pigs to establish the normal range. Then the same test was used in a group of 49 guinea pigs with endolymphatic hydrops induced by immunologic techniques. They did not show spontaneous nystagmus or body deviation while walking, but a total of 20 out of 49 animals displayed abnormal swimming patterns, with 8 swimming clockwise and 4 counterclockwise. This swimming test is easily able to detect mild vestibular dysfunction in guinea pigs, and can be repeated, so that we consider it useful for examining vestibular function in these animals.

Global balance of inner and middle ear pressure is controlled by the cerebrospinal fluid inside and the atmospheric pressure outside. The cochlear and vestibular aqueducts and the Eustachian tube, connected by a one-way communication, provide a fine control over inner and middle ear pressure.

In the last 15 years, a pressure chamber able to generate negative air pressure has been used to treat patients with Menière's disease. In this study we sought to clarify whether the underpressure chamber can be used to diagnose Menière's disease. We studied 45 ears from patients with neurotological diseases. The subjects were placed supine in a soundproof pressure chamber. The pressure was first decreased to -500 mmH2O, and after 5 min to -700 mmH2O. The pressure was kept at this level for another 5 min and then increased to 0 mmH2O. This procedure was done three times in succession. While the chamber pressure was below 0 mmH2O, the subjects were instructed to abstain from actively equilibrating middle ear pressure. When the chamber pressure was raised to 0 mmH2O, they were instructed to equilibrate middle ear pressure, and if necessary Politzerization or catheterization of the Eustachian tube was done. As a result, hearing was improved after this procedure only in patients with Menière's disease (50%) and/or cochlear Menière's disease (32%) in which endolymphatic hydrops was suspected.

The responses of primary vestibular neurons and perilymphatic pressure changes to middle ear pressure were investigated in guinea pigs with obstructed vestibular or cochlear aqueduct (closed VA or closed CA group) in order to clarify the influence of VA and CA on pressure-induced vestibular response. Although the neural response rates and the amount of perilymphatic pressure change in the closed VA group resembled those in the control group, these values in the closed CA group were higher than in the control group. Patency of the CA had a more significant effect on the vestibular response to middle ear pressure change than patency of the VA.

Although bilateral involvement of Meniere's disease is serious enough to produce deafness in both ears, actually little attention has been directed to such involvement. Recently, several reports have been made concerning the bilateral aspects of this disease (1-8). However, lacking mutual agreeable diagnostic criteria for making these reports and differences in characteristics of patients with Meniere's disease among institutes makes it difficult to establish definitive interpretations. In 1988, the Vestibular Disorder Research Committee made a survey among 15 committee member institutes using the same diagnostic criteria of bilateral involvement of Meniere's disease. Based on the results obtained, in this paper, incidence and characteristics of bilateral cases in Meniere's disease will be discussed.