With the aid of diffusion computer the Fourier transform has generally been used to analyze the frequency responses of various bioelectric signals. We have introduced this method in the analysis of the following equilibrium tests 1) Frequency analysis of the body sway test. 2) Quantitative analysis of the galvanic body sway test. In this analysis the inverse Fourier transform is used to detect frequency components of body sway responses corresponding to galvanic stimulations. 3) Computation of the gain and phase lags of the vestibulo-ocular reflex in the pendular rotatory test. 4) Analysis of the influence of linear acceleration on caloric nystagmus. Although the Fourier transform can be applied simply by computer, a wrong diagnosis can result of analysis if it is applied without a full understanding this method. This paper describes the fundamental theory and practice of the Fourier transform in equilibrium tests.
Convergence nystagmus was obserbed in a 54-year old man with familial spinocerebellar degeneration. Neurological findings showed cerebellar ataxia including dysmetria with scanning speech, gait disturbance and horizontal diplopia. The mother, 4 of the 7 siblings and her maternal grandmother had a similar history. NMR-CT revealed significant atrophy of the brainstem and cerebellum. Convergence nystagmus was present in the primary position and was accentuated by convergence on ENG. Other neurotological findings showed bilateral horizontal gaze nystagmus, which was marked in adducent eyes, direction-changing positional nystagmus to the lower ear on the upper eye only, impaired OKN in the horizontal planes which was marked in abducent eyes during quick phase and saccadic pursuit. Cold caloric stimulations elicited tonic eye deviation in the direction of the slow phase on each side. Neurotological findings suggested impairment of the bilateral eye movement system in the midbrain, pons and vestibulocereberum. There was no case of spinocerebellar degeneration among the 74 cases of convergence nystagmus reported in the literature.
In this investigation of the interactions between the optokinetic and vestibular systems, a pendular optokinetic nystagmus (P-OKN) test was carried out on 34 normal subjects and compared with the pendular rotation tests (VOR and VVOR tests) and OKN tests used previously. The subjects sat in a pendular sinusoidal rotating chair in an optokinetic drum, which provided pendular sinusoidal optokinetic stimulation. The optokinetic stimuli were at an amplitude of 120 degrees (total amplitude of 240 degrees) at frequencies of both 0.05Hz and 0.1Hz. With this stimulation there was no response decline phenomenon. The VVOR is considered to be the result of a synergistic interaction of the VOR and OKN. In our investigations the contribution from the vestibular system was 7 per cent with 0.1Hz frequency rotation. However, with 0.05Hz frequency rotation the contribution was very small. The gain of P-OKN, with slow phase velocity as a measure, was higher than that of OKN during linear acceleration and approximately equal to that of OKN induced by constant velocity stimuli. The P-OKN test is a simple and useful test of the function of the oculomotor system, so it may become a screening test for central nervous system disorders.
We otoneurologically analyzed patients with vertigo and/or dizziness associated with unilateral or bilateral occlusive disorders of vertebral artery system, and the results were compared with those of healthy age-matched controls. More than half of the vertiginous and/or dizzy attacks were induced by postural change and/or neck torsion. The results of the ETT test revealed more abnormalities in the bilateral disorders than in unilateral disorders. The slow phase velocities of OKN at higher target speeds were significantly reduced in the patients compared with the control groups. Thus further otoneurological and vertebral arteries examinations are required to detect abnormalities of the vertebral artery system in the younger vertiginous patients who show reduction of slow phase velocities of OKN at higher target speed.
The purpose of this study is to investigate the quantitatively characteristics of body sway in older subjects standing in Romberg' posture. We compared body sway of older subjects with that of young subjects. 1. The area and locus length traced by the body's center of gravity (CG) was increased in older subjects and especially with eyes closed. 2. Normal variations were large in older subjects. 3. The standard deviations of each amplitude of CG movement increased in the antroposterior (A/P) direction. 4. The average spectoral frequencies (0-1.0Hz) increased in A/P direction. 5. The average spectoral frequencies (0.12-1.0Hz) decreased in the lateral direction with eyes open and increased in the A/P direction with eyes closed.
We examined postrotatory nystagmus in 43 patients with vertigo. The slow phase of postrotatory nystagmus was analyzed by a second order system represented by the following equation. y (t) =A (e-t/T2-et/T1) /T2-T1 y (t) =slow phase of postrotatory nystagmus (°/sec). T1=short time constant of system of postrotatory nystagmus (sec). T2=long time constant of system of postrotatory nystagmus (sec). Calculation was done by the most-least square method and values A, T1, T2 were determined. The values of 15 healthy subjects without any ear or brain disease were used to determine the normal range. In 43 patients with vertigo the short time constant had no relation to the attacks of vertigo; however, the long time constant was shortened in parallel with the degree of vertigo. Ampllopetal flow in the affected ear, especially during vertigo, showed a shorter than normal long-time constant. We conclude that patients with vertigo have a shorter long-time constant and a low AP value. This means that patients with vertigo are intolerate of longer stimuli.
We report here a rare case of fourth ventricular ependymoma in an adult. A 42-year-old woman has complained of vertigo vomiting and headache for three months duration. Vertigo gradually worsened and she admitted to our hospital. Neurootological findings were : retrolabyrinth hearing impairment on the left side, continuous-right-directional gaze nystagmus and positioning nystagmus, and saccadic eye movement in the eye tracking test. Slow phase velocity of OKN was limited bilaterally, especially on the left side. Base on these findings, a diagnosis of forth ventricular tumor was made. Surgery revealed an ependymoma. Now, two years have gone after our treatment. Ependymoma was no recurrence.
Modulation by head and trunk positions of the vestibulo-spinal reflexes was studied with respect to soleus muscle activities induced by galvanic stimulation of the labyrinth (labyrinthine evoked EMG). A subject was asked to stand with eyes closed and was stimulated with galvanic current by a bipolar-biaural method with the cathode on the right ear and the anode on the left ear. The intensity was 1mA and duration was 3s. The vestibulo-spinal responses induced by the stimulation were examined in terms of the activities of both soleus muscles. When the labyrinth was stimulated with the head facing forward, soleus muscle activities increased on the right side and decreased on the lift side with a latency of about 100ms. When the head was rotated to the right, both soleus muscle activities decreased. When the head was rotated to the left, both soleus muscle activities increased. Despite the same labyrinthine stimulation, soleus muscle activities provoked by galvanic stimulation with the head turned to the right were opposite to those with the head turned to the right. Changes by upper-body rotation of the labyrinthine evoked EMGs was similar to those by head rotation. When the trunk was rotated to the right and left with the head and lower body kept stationary, galvanic induced soleus activities were similar to those with the trunk facing forward in 3 of 6 subjects. However, 3 other subjects showed modulated response induced by head rotation, indicating that the influence of head position was stronger than that of waist position. We speculate that the properties of the vestibulo-spinal responses are due to interaction of vestibular and proprioceptive inputs on the interneuron of the spinal cord.
We recorded repeated caloric tests of 53 patients treated with streptomycin sulfate (SM) and measured the maximum slow phase velocity of caloric nystagmus. The maximum slow phase velocity often decreased below 10°/sec before the patient noted symptoms. However, it increased again above 10°/sec in one month when SM injections were stopped within 1 week after it had decreased below 10°/sec. On the other hand, no such increase was observed after 4 months of treatment. When it was above 10°/sec at the time of drug cessation, it showed no further change. These results suggest that 10°/sec of maximum slow phase velocity of caloric nystagmus is a critical level for the detection of subclinical functional damage of the vestibule in patients receiving SM injections but not complaining of subjective symptoms, and that this functional damage, if present, seems to be reversible with prompt discontinuation of SM injections.
A 41-year-old woman suddenly noticed hearing loss and tinnitus of the left ear. She did not experience any vertigo. Sudden deafness was suspected, and she was treated with steroid hormone intravenously 4 days after the onset of hearing loss. Audiometric testing revealed a sensorineural deafness with an average of 63 dB. The response to caloric stimulation was normal in both ears. Stenvers view showed no abnormalities. Two weeks after treatment the hearing in her left ear recovered to 26 dB. in pure tone average. Twenty seven months later she consulted an ophthalmologist with a complaint of headache and myodysopsia. Papilledema was noted. CT disclosed masses in the right frontal lobe and left cerebelloportine angle. Stenvers view showed normal internal auditory canal in both ears. Pure tone audiogramas revealed sensorineural hearing loss with an average of 72 dB. in the left ear. Caloric response was absent in both ears. A meningioma in the right frontal lobe and an acoustic neurinoma in the left cerebellopontine angle were removed by neurosurgeons. The authors stress that patients with sudden deafness should be followed after treatment for as long as possible, even if hearing is improved by medical treatment, and that ABR is desirable in the diagnostic evaluation of acoustic neurinoma.
A cell culture study was performed using vestibular ganglion cells from 10 chick embryos and 64 fetal rats. Vestibular ganglion cells of various shapes could be incubated. Bipolar cells and two types of multipolar cells, small round cells and large cells, were observed. Vestibular ganglion cells were found to be very irregular in size.
Seventy-four healthy subjects between the ages of 65 and 88 years (mean=75 years), 21 men and 53 women, underwent the caloric test. The subjects were divided into two groups; 65-74 and 75-88 years of age. The caloric test was also performed in 20 healthy young individuals 20-29 years of age as a control group. The ears were irrigated with 20ml of ice water for 20 seconds. Caloric nystagmus was recorded by ENG with the eyes kept open in darkness. The total number of beats, the duration of nystagmus, the maximum velocity of the slow phase and the latent time of the nystagmus were recorded. The results in the elderly subjects were compared with the findings in the control group. 1) The caloric reaction, measured by the duration of nystagmus and maximum velocity of the slow phase, appeared to be significantly decreased in the 75-88 years age group. 2) Functional asymmetry of caloric response was revealed at the parameter maximum velocity of the slow phase in 5 subjects over 65 years of age. 3) All the members of the control group complained of definite rotatory vertigo, but 12 subjects (8.1%) more than 65 years of age had no sensation of dizziness. 4) Our investigation indicates that the caloric response is generally well preserved up to a highly advanced age.
Thirty-three patients with positional vertigo caused by peripheral vestibular lesions were divided into two types of positional nystagmus on the basis of the direction of nystagmus (horizontal or rotatory) and head positions which induced positional vertigo. One type of positional nystagmus was characterized by direction-changing horizontal positional nystagmus, directed towards the lower part of the ear when the right side was down or the left side was down. This type of positional vertigo was provoked by turning over in bed. The other type of positional nystagmus was characterized by direction-changing rotatory positional nystagmus, which was induced mainly by head positioning in the sagittal plane. This type of positional vertigo was provoked by lying down or getting up. Furthermore, horizontal positional nystagmus was induced strongly only by head rotation in the supine position and not induced (or only weakly induced) by head rotation in the sitting position or the hanging position. The electrophysiological experiments of Fernández and Goldberg showed that the right side down and left side down positions were typical positions in which utricular neurons were very sensitive to gravity. It was specurated that horizontal positional nystagmus might be caused by utricular dysfunction.
Using Contraves' computerized rotary chair system, sinusoidal harmonic acceleration (SHA) test and trapezoid rotation (TR) test were performed on the same day on 25 normal subjects and 110 patients with the peripheral vestibular disorders, to evaluate the meaning of “phase lag” detected by the SHA test. The patients tended to show lower “gain” of VOR by TR test, and a more dominant “phase lag” was recorded by SHA test. A “phase lag” was detected by SHA test in 56.5% of the subjects, and this incidence was similar to that of “vestibular asymmetry” detected by TR test. Although “vestibular asymmetry” was frequently detected in the vertiginous stage, “phase lag” was noted not only in the vertiginous stage but also in the non-vertiginous stage of the peripheral vestibular disorder. “Phase lag” was thought to be a useful parameter of abnormality of the vestibular system.
Hearing and vestibular function tests were performed before and after hemodialysis in 14 patients with renal failures. In 3 cases, transient hearing disturbances at 4, 6 and 8kHz were observed after hemodialysis. In 2 of them, hyper-lipidemia were detected. Peripheral positional nystagmus was observed in 5 patients, and, after hemodialysis, it tended to change in the direction of the undermost ear. This suggest that direction changing nystagmus was caused by alteration of the specific gravity of the inner ear fluid. After hemodialysis, the optokinetic nystagmus pattern (=OKP) became worse in 3 patients, and 2 of them had episodes of hypotension during hemodialysis.