Astronauts and scientists are scheduled to stay aboard the International Space Station (ISS) for three-month periods, and various problems relating to the human ability to live in space for such long periods of time, as well as medical problems, are being studied. For the crews that have operated and worked on the US space shuttle, the longest time spent in the gravity-free (accurately speaking, microgravity) environment of space has been about two weeks. Even such short periods have generated reports of various physical changes and symptoms caused by the absence of gravity. Particularly striking effects are circulatory system changes, muscular atrophy and decalcification of bones. In addition, serious problems arise during the time in space due to the symptoms of space motion sickness, caused by neuro-otological changes. Space motion sickness is experienced by nearly 70% of first-time astronauts, in the form of such symptoms as nausea, and vomiting. It is said that space motion sickness develops at the time of adaptation of the body to the gravity-free environment. Unlike motion sickness on Earth, space motion sickness is characterized by a feeling of fullness of the head, a hot face and reduced sweating. The provocative factors include movement of the head in the pitch and roll directions and the unusual visual field. This paper reviews the research that has been carried out to date on space motion sickness. It also discusses the need to consider the mechanism of the development of space motion sickness and its counter measures comprehensively, in terms of the changes in the otolith organ as well as asynchronization of information between the movements of the head and eyeballs, the deep sensations and body fluid shifts. Other problems, which may be encountered as a result of yet longer stays in space, are also discussed.
In our previous reports we hypothesized that both vertigo and deafness in Meniere's disease could be explained by high potassium levels in the scala tympani, not in the scala vestibuli. High potassium levels in the scala tympani may be caused mainly by the increased diffusion of potassium through the distended Reissner's membrane. A relative decrease in the perilymphatic space due to endolymphatic hydrops might also play an important role in the elevation of potassium levels in the scala tympani. Thus, the aggravation of vertigo and deafness is closely linked to the degree of hydrops. In Meniere's disease, vertigo and deafness is often induced by stress. Stress is well known to promote the release of vasopressin, resulting in an increase in plasma vasopressin. We previously reported that an increase in plasma vasopressin was observed in Meniere's disease. Although histological and surgical findings support the hypothesis that the dysfunction of the endolymphatic sac is one of the important factors in Meniere's disease, we speculated that a high concentration of plasma vasopressin may be the other causative factor in the formation of endolymphatic hydrops.
Numerous studies have been performed to elucidate the mechanism of hair cell death in the inner ear following various ototoxic treatments, and a predominant role of apoptosis in the deletion of damaged hair cells has been revealed. In addition, recent investigations have indicated involvement of caspases, Bcl-2 family, cytochrome c and c-Jun in the process of apoptosis of inner ear hair cells. Oxidative stresses and nitric oxide were also hypothesized to play a certain role in the induction of apoptosis after ototoxic treatments. However, the precise relationships among these molecules in the apoptotic pathway of hair cells still remain unclear. Future studies are necessary to clarify the signaling cascades of apoptosis in either vestibular or auditory hair cells. This may contribute to the elucidation of the mechanisms of ototoxicity and the establishment of new therapeutic strategies for inner ear disorders.
The purpose of this study was to investigate whether Magnetic Resonance Angiography (MRA) with single photon emission computed tomography using I-123 iodoamphetamine (IMP-SPECT) can distinguish peripheral vestibular disorders (PVD) from central vestibular disorders (CVD) in elderly vertigo patients. Of a total of 65 patients, 30 patients who were clinically diagnosed with PVD, and 35 patients diagnosed with CVD were enrolled in this study. We investigated blood flow in the posterior brain consisting of the upper medulla, bilateral hemisphere and occipital lobe using IMP-SPECT and compared blood flow with MRA findings. Posterior brain blood flow (BBF) in PVD patient's was significantly higher than that in CVD patients (P<0.05). The number of patients in MRA types, I, II, III and IV was 34, 18, 4 and 9 cases, respectively. BBF in each area of the posterior brain in patients, with type IV was significantly lower than that in patients with other MRA types (P<0.05). All of the type II cases revealed hypo form of vertebral artery. The number of PVD patients was significantly higher than that of CVD (P<0.05) in type II. From these findings, we suggested that the pathogenesis of CVD is closely connected to the insufficiency of the posterior BBF and that MRA with SPECT findings in the diagnosis of vertigo patients is very effective in distinguishing CVD from PVD. Some patterns of MRA with SPECT may correspond to insufficiency of vertebrobasilar blood flow. We consider that in vertigo patients, MRA with IMP-SPECT examination is useful not only to assist in the elucidation of etiology but also to predict the stage of vertebro-basillar insufficiency in each patient.
In this study we used the trapezoid rotation test to evaluate vestibular function in normal guinea pigs or guinea pigs with peripheral vestibular disorder. Post-rotatory nystagmus (PRN) was recorded on videotape under dark conditions with an infrared charge-coupled device camera. The analysis was performed using the pubic domain NIH Image program, and the horizontal and vertical components were calculated automatically. The mean value of maximum slow phase velocity (MSPV) in the normal guinea pigs and guinea pigs with vestibular disorder was 37.288±9.423 degree/sec and 9.786±2.758 degree/sec respectively. There was a significant correlation between the PRN number and MSPV. We consider that this system makes it possible to evaluate vestibular function in animal models easily and inexpensively.
In this study we classified stabilograms to elucidate the characteristics of sway in the body center of the gravity using principal component analysis and neural network (NN) in 826 healthy subjects. Stabilography was performed with eyes open and closed with both feet close together for 60 seconds using a stabilometer. The area, length/time, length/area, power spectrum, position and velocity vectors and standard deviation and kurtosis of amplitude histogram were measured. Principal component analysis and classification using NN were conducted using the measurement values. Principal components were calculated by 80% of the cumulative proportion, and 5 components were obtained. From the eigenvectors of the 5 components, 8 sway types were found and these were used to classify the sways of the 826 subjects. Learning by NN was carried out with measurement values obtained from the sways represented by each pattern, and a weighted NN was obtained with an error of 0.005. Stabilograms of healthy subjects were classified using the weighted NN into 9 sway types; large sway type, low frequency type, high frequency type, forward-backward enlargement type, right-left enlargement type, centripetal type, forward-backward sway type, right-left sway type, and non-specific type. We considered that the NN classification of stabilograms was useful for the observation of daily fluctuation of equilibrium function in healthy subjects.
We report 5 patients who complained of dizzy sensations while driving on the freeway. All 5 patients were male and had no history of dizziness or vertigo in daily living other than automobile driving. On neuro-otological examinations, direction-fixed nystagmus was observed in three patients, and unilateral low-tone hearing loss was suspected in three. Body equilibrium tests, caloric test, electronystagmographic examination (ENG), and vestibular evoked myogenic potential (VEMP) showed no definite abnormalities. Visual, vestibular, proprioceptive and psychological factors are considered to be important to maintain equilibrium during driving, and in all 5 cases there was some evidence of vestibular disorders. Driving on the freeway induces a narrow visual field in proportion to automobile speed, and reduced visual information. Visual sight plays more important role in maintenance of the body balance in patients with peripheral vestibular disorders; thus, a slight imbalance of vestibular tone may cause dizziness during driving on the freeway.