This article describes the basic elements of auditory evoked potentials, including stimulus tone and recording condition, and clinical applications of auditory evoked potentials, such as ECochG, ABR and ASSR. The clinical applications of auditory evoked potentials are roughly classified into (1) objective audiometry and (2) neurological examination. ECochG is applied to the diagnosis of endolymphatic hydrops and inner ear hearing loss. ABR is still an important examination in the diagnosis of acoustic neurinoma, though the prevalence of MRI has reduced its importance. The elongation of the I-V inter-peak latency (I-V IPL) of ABR in lower brainstem lesion is mainly due to I-III IPL elongation, whereas I-V IPL elongation is mainly due to III-V IPL elongation in upper brainstem lesions. Recruitment and conductive hearing loss can be estimated by the finding of the latency-intensity curve of wave V. Although ABR is the most popular device in objective audiometry, the prediction of hearing levels in the lower frequency range using ABR evoked by clicks is less accurate. The most important benefit of ASSR is to provide an accurate assessment of hearing at different frequencies in a frequency specific manner, if stimulation consists of a sinusoidally amplitude-modulated tone. However, ASSR is not appropriate to use as a diagnostic tool in neurological examinations, because the waveforms of ASSR consist of the interference of different wave components. Power spectrum analysis and phase coherence using fast Fourier transformation are useful for the automatic detection of ASSR, because of its sinusoidal waveform configuration. Because the detectability of ASSR changes under different arousal states, 40-Hz ASSR is suitable for waking adults and 80-Hz ASSR for sleeping children in the assessment of hearing. Its advantage is that the thresholds at 4 different frequencies in both ears can be predicted more rapidly than ABR using the multiple simultaneous stimulation technique.
This study was performed to determine if a new treatment was effective for cases with benign paroxysmal positional vertigo (BPPV) suggesting cupulolithiasis of the horizontal semicircular canal as characterized by apogeotropic direction-changing nystagmus. We describe herein our head-tilt hopping (HtH) exercise designed to release and move otoconia adhesive to the cupula. Subjects were trained to hop with their heads tilted laterally. They completed 3-5 training sessions a day over a 4-week period. Each session ended with a 20-hop trial. HtH exercises were performed in 14 cases with intractable horizontal canal BPPV exhibiting persistent nystagmus beating toward the uppermost ear. The spine roll test was tested on all subjects before and immediately after the first trial, as well as after 1 and 4 weeks of the training to evaluate the effect of this treatment on the apogeotropic nystagmus. The nystagmus disappeared or decreased immediately after the first trial with the exercise in 3 and 2 of 14 cases, respectively. The number of subjects showing improvement as assessed by the disappearance or decrease of the nystagmus were in 9 (64.3%) and 11 (78.6%) of all cases tested at 1 and 4 weeks' time, respectively. However the remaining 3 subjects were not affected by this treatment program after 4 week of the training. These results suggest that HtH exercises based on the concepts of release of otoconia from the cupula would appear to be feasible as a new therapy for cupulolithiasis associated with intractable horizontal canal BPPV
The vasovagal reflex (VVR) is a reflex reaction in which abnormal autonomic system activity may be involved, and it has been known as a cause of dizziness and syncope following standing up quickly, drawing blood and after exercise. We report on a case where an exercise test was used to clinically confirm dizziness due to the VVR. A 17-year-old-male visited the clinic complained of recurring dizziness during exercise. He underwent brain computed tomography, ECG, and master ECG at another hospital. The VVR was caused when drawing blood. The head up tilt test was performed, but the test was negative. Thus, an exercise test was performed to confirm the diagnosis. The subject steps up and down on a stair until he complain of sensations such as dizziness nausea and syncope. Heart rate and blood pressure are checked every 5 minutes during exercise and before and after the exercise test. The exercise test was negative. But the VVR attack recurred together with bradycardia (36 beats/min) 4.5 minutes after the test. A diagnosis of the post-exertional syncope type of vasovagal reflex was made.
In our practice, we often encounter dizzy patients in whom organic and functional abnormalities are lacking, as assessed by a variety of clinical examinations. In these patients, anxiety and depression are strongly related to their clinical symptoms. We diagnose these patients as having “psychogenic dizziness” and treat them with antidepressants and anxiolytics. Although therapeutic evaluation of patients' subjective complaints and objective evaluation by doctors are usually performed, an objective measurement is necessary to determine whether the drug treatments are effective. In the present study, we used static posturography to objectively evaluate the therapeutic response to antidepressant and anxiolytic treatments in patients with psychogenic dizziness. Thirty-seven patients with psychogenic dizziness participated in this study. All patients were prescribed antidepressants and anxiolytics. We assessed each patient using static posturography before treatment and 4 weeks after treatment. Static posturography was performed for 60 seconds with the patients' eyes open and closed. The Clinical Global Impressions-Improvement (CGI-I) scale was used for global evaluation. On the basis of the CGI-I scores, the subjects were divided into two groups: I, improved (≤3), and N, not improved (≥4). The following static posturography measurements were used for comparison: length (LNG), environmental area (ENV), and LNG/ENV. For each of these parameters, we determined improvement rates by calculating the difference between before- and after-treatment measurements. We found that CGI-I scores correlated with LNG, ENV with eyes open, and ENV with eyes closed. The improvement rates of groups I and N were significantly different for all parameters. Data obtained from subjects that had lower improvement rates relative to control values were selected for further analysis. Control values were obtained from 2201 normal subjects. Group I subjects that had low LNG/ENV values (with eyes open) before treatment showed significantly increased LNG/ENV values (with eyes open) after treatment. Our analyses revealed statistically significant differences between groups I and N in some static posturography values obtained before and after treatment. Our findings indicate that static posturography values can be used to objectively evaluate psychogenic dizziness in future studies.
The vestibular organs consist of three semicircular canals, which sense angular acceleration, and two otolith organs, which sense linear acceleration. Although we are now exposed to various degrees of linear acceleration with the development of advanced methods of transportation, less is known about the function of the otolith organs relative to the function of the semicircular canals. There are several reasons for this: the morphological and functional characteristics of the otolith organs are complex; the otolith organs respond not only to dynamic head translation but also static head tilt with respect to gravity, and it is difficult to generate sufficient linear acceleration using a compact apparatus. To clarify otolith function, this article introduces recent progress in studies of the linear vestibuloocular reflexes, which are eye movements that compensate for linear translation or tilt.
Since our visual sense performs its best analysis when images remain steady on the retina, the eyes may need to move in order to track an object. To move the eyes, optokinetic and vestibular reflexes evolved to stabilize images on the retina during head movements. The vestibular and optokinetic systems work together to maintain clear vision during head movements. Because natural head movements occur with high frequency, the visual system is impeded by relatively slow retinal processing (about 70 msec), and cannot adjust rapidly enough to produce compensatory eye movements that would hold images steady on the retina. In contrast, the semicircular-ocular reflex (ScOR) has a latency of less than 16 msec. The ScOR promptly produces slow phase eye movements to compensate for head rotations. The vestibular system also contains otolithic receptors that respond to linear accelerations of the head. The otolith-ocular reflex (OOR) becomes important when head translations cause a slip in the image on the retina. Normally occurring head motion has both rotational and translational components so that both the semicircular canals and otolith organs contribute to the generation of compensatory slow phase eye movements. To evaluate the ScOR, caloric and rotational tests are routinely used. However, there is no practical test of the OOR in clinical use. The development of an otolith function evaluation tool is potentially important, because disorder of the otolith organs may underlie the complaints of some undiagnosed vertigo patients. There are many methods of stimulating the otolith organs, all of which include some form of linear acceleration. In this paper, I will describe a linear sled, eccentric VOR (EVOR) and off-vertical axis rotation (OVAR), which are considered useful and practical methods for evaluating the OOR in clinical practice.
In humans, a positive followed by a negative waveform with short latency is reproducibly evoked in the sternocleidomastoid (SCM) muscle in response to intense sound. This sound-evoked vestibulocollic reflex is termed the vestibular evoked myogenic potential (VEMP). We investigated the characteristics of the VEMP as an otolith function test. The human VEMP has its best frequency located between 500 Hz and 1 kHz that resembles a V-shaped tuning curve of the saccular nerve in cats, recorded in the inferior vestibular nerve. The amplitude of the human VEMP was enhanced under microgravity during parabolic flight and was attenuated by the rostro-caudal linear acceleration on Earth. These findings suggest that the human VEMP is an otolith function test and originates from the saccule. After vestibular deafferentiation, unilateral VEMP dysfunction in the affected side appears and lasts for a long time. In patients with inner ear and retrolabyrinthine disorders, abnormality of the VEMP was not always coincident with that of the caloric test. These findings suggested that the VEMP, like the caloric test, is another important tool for the diagnosis of the affected side, and that a test battery of the VEMP and caloric test may help to increase the rate of abnormal findings among patients with the peripheral vestibular disorders. In the human VEMP, activation of acoustically responsive saccular afferents triggers an acoustic reflex in the SCM muscle. Future studies are needed to clarify in detail, the clinical usefulness of the VEMP as an otolith function test.
Many papers had been published regarding clinical applications of the vestibular evoked myogenic potential (VEMP). The most important feature of the VEMP is measureable without specific devices. From a standpoint of the feature, furosemide loading VEMP (F-VEMP) testing and bone conducted VEMP (B-VEMP) are described in this paper. Furosemide loading VEMP testing diagnosis of endolymphatic hydrops: The amplitude of the p13-n23 biphasic wave before (AB) and 60 minutes after (AA) 20mg of furosemide administration were measured. The improved ratio (IR) was calculated by the following formula: IR(%)=100×(AA-AB)/AB. If IR exceeded 43.5% or if a biphasic wave was detected after administration when the wave could not be detected before administration, the result of the F-VEMP test was considered to be positive. Positive results were shown in 40% of the affected ears in Meniere's disease patients. The ratio was similar to that of the conventional examinations for endolymphatic hydrops. Bone conducted VEMP for vestibular examination in patients with perforated ear: The relationship between air-conducted VEMP (A-VEMP) and bone-conducted VEMP (B-VEMP) was studied in patients with unilateral vestibular disorders. The inter-aural ratio of B-VEMP was strongly correlated to those of A-VEMP. B-VEMP in patients with conductive hearing loss due to perforated ear were studied. Abnormal results were not found in any subjects without disequilibrium but were found in 54.0% of subjects with disequilibrium. The perforated ear showed lower responses than the intact ear in all subjects with abnormal results. Vestibular function can be evaluated with B-VEMP in patients with conductive hearing loss. Conclusion: VEMPs are useful to examine the following conditions, 1. Furosemide loading VEMP a. Diagnosis of Meniere's disease b. Diagnosis of endolymphatic hydrops in ears with normal hearing function c. Diagnosis of endolymphatic hydrops in ears with abnormal hearing function 2. Bone-conducted VEMP a. Examination for vestibular function in perforated ears
The author showed variants of the vestibular evoked myogenic potential (VEMP), which have been developed as a myogenic potential evoked on the sternocleidomastoid muscle by air-conducted sound (ACS). The prototype of the VEMP is called the ACS cVEMP (cervical VEMP). Firstly, the author introduced VEMP by bone-conducted vibration (BCV). While ACS VEMP is not applicable to subjects with conductive hearing loss, BCV VEMP can be recorded even in such subjects. Examiners of BCV VEMP should bear in mind that BCV can stimulate wider areas in the vestibular labyrinth than ACS. Secondly, the author described VEMPs recorded using electrodes placed beneath the lower eye lids, which is called oVEMP. While cVEMP is recordable in the SCM ipsilateral to the stimulated ear, oVEMP is clearly recorded in the electrodes beneath the lower eyelid contralateral to the stimulated ear. oVEMP is promising as a new test of vestibulo-ocular reflexes, especially otolith-ocular reflexes. The author also emphasizes that further studies to identify the vestibular end-organs and extra-ocular muscles which participate in formation of oVEMP responses and the neural pathway of oVEMP are required.