The effects of chronic increased lead absorption on the nervous system--a review article.
Explore the source record for details and available documents.
Adult↗
Biomedical subjects
R W Baloh
Publications and source records attributed to R W Baloh.
Intradural arachnoid cyst presenting with cord compression. Report of a case and review of the literature.
Explore the source record for details and available documents.
Adult↗
The vestibular system in the elderly: clinical implications.
Cell loss, changes in synapse morphology, electrophysiologic alterations, and changes in the supporting microenvironment have all been noted in portions of the vestibular systems of aged animals and humans. Increased variability with age is also a prominent finding in many studies. Quantitative vestibular testing in humans has shown alterations with age as well, but decline with aging is not a prominent feature of all measures, and many reported studies are methodogically flawed. The connection between these observed aging changes and the increased incidence of dizziness and falls in the elderly is unproven, however, and clinicians should search carefully for specific disease processes in their elderly patients who present with vestibular symptoms.
Age Factors↗
Habituation of the human vestibulo-ocular reflex with low-frequency harmonic acceleration.
Habituation of the human vestibulo-ocular reflex by prolonged low-frequency (0.01 and 0.005 Hz) harmonic (sinusoidal) angular acceleration was assessed by measuring the phase advance of slow-phase eye velocity at 0.01 Hz and the time constant of slow-phase eye velocity decay after impulses of angular acceleration. A single half-hour test session produced increases in low-frequency phase advance and decreases in time constant values in all 16 normal subjects. Although all subjects showed increases in low-frequency advance from the beginning to the end of the initial test session, only a few maintained the increases between test sessions. These changes are qualitatively similar to but quantitatively less than those observed with similar testing in monkeys. For clinical testing, to minimize the effect of habituation during harmonic accelerations, the testing time at low frequencies (i.e., less than 0.1 Hz) should be as short as possible.
Acceleration↗
Vestibulo-ocular reflexes in peripheral labyrinthine lesions: I. Unilateral dysfunction.
Measurements were made of the lesion-induced changes in vestibulo-ocular reflexes to rotatory stimuli in a group of patients with total unilateral labyrinthine paralysis and in a group with partial unilateral labyrinthine paralysis. Significant differences were found in the amplitude and phase of the response to low-frequency rotation and in the time constant of the post-rotatory response to impulsive rotation between normal subjects and patients with total unilateral labyrinthine paralysis. The results were evaluated by the use of a simplified model of vestibular function that allows the parametric evaluation of the characteristics of vestibular responses. It was found that changes in vestibulo-ocular reflex characteristics take place in parallel in both the time constant and the sensitivity of the system parameters used to describe the responses. The physiologic significance of the changes and their implication for diagnostic purposes are discussed.
Electrooculography↗
Vestibulo-ocular reflexes in peripheral labyrinthine lesions: II. Caloric testing.
In a group of patients with unilateral labyrinthine dysfunction, the maximal velocity of the slow component response to caloric stimulation was compared with that to horizontal vestibular rotatory stimulation by a low-frequency stimulus. It was found that the larger the magnitude of the caloric response, the larger were the gain and sensitivity of the vestibulo-ocular reflex induced by physiologic stimuli. Rotary stimulation of patients with only one functioning inner ear provides information equivalent to that obtained from caloric stimulation and allows more rigorous quantification of the state of the vestibulo-ocular reflex.
Caloric Tests↗
Vestibulo-ocular reflexes in peripheral labyrinthine lesions: III. Bilateral dysfunction.
Measurements were made of the lesion-induced changes in vestibulo-ocular reflexes (VOR) to rotatory stimuli in a group of patients with bilateral peripheral labyrinthine lesions. All the patients had caloric responses that were below the confidence levels used for normal responses in our laboratory. Responses to rotatory stimuli were greatly decreased or absent at low frequencies of stimulation, but present to a much greater degree at the higher frequencies. Phase measurements showed an increase in relationship to the velocity of the stimulus; there was a corresponding shortening of the time constant as obtained from impulse response measurements. A parametric study indicated that the changes in the responses can be described by a decrease in the sensitivity coefficient and in the basic time constant of a simplified pendulum model equation of vestibular function. A theoretical analysis of the data using a new model for the organization of the vestibular pathways indicated that the preservation of the high-frequency responses was the result of adaptive changes brought about in the central vestibular pathways and/or changes in the receptor-neuron transduction characteristics. Thus, despite the almost complete absence of any caloric response, the vestibular system reflexes remained adequate to maintain gaze during normal head movements.
Adult↗
Vertical vestibulo-ocular reflex in patients with benign paroxysmal positional nystagmus.
The vertical vestibulo-ocular reflex (VOR) was tested in 13 patients with benign paroxysmal positional nystagmus and in ten normal subjects. Patients and normal subjects were rotated in the sagittal plane and in the plane of the vertical semicircular canal pairs using sine and step stimuli. Gain, phase, and time-constant measurements of the vertical components of induced nystagmus were not significantly different (P greater than normal 0.05) in the normal subjects and patients for any test condition. At least for the range of test stimuli used in this study, the dynamics of the vertical VOR were normal in patients with benign paroxysmal positional nystagmus.
Electrooculography↗
Direction-changing positional nystagmus: incidence and meaning.
Direction-changing positional nystagmus (DCPN) is a nystagmus that changes its direction with different body and head positions. Many authors consider that it indicates the presence of a central nervous system lesion. Of 1,196 patients whose abnormal electronystagmographic (ENG) traces were reviewed, 46 (3.8 per cent) showed DCPN. Of these, ten (22 per cent) had central neurologic diseases, 14 (30 per cent) had peripheral vestibular diseases, and for 22 (48 per cent) there was no definite clinical diagnosis. Nineteen patients (41 per cent) with DCPN had ENG findings suggesting a peripheral vestibular lesion, while only five (11 per cent) had ENG findings suggesting a central vestibular lesion. Four of 44 control subjects exhibited DCPN. Thus, the presence of DCPN does not necessarily indicate disease of the vestibular system and definitely does not localize the site of a lesion in the vestibular pathways, but more often indicates a peripheral vestibular site. As with spontaneous nystagmus, lack of suppression with fixation suggests a central lesion.
Adult↗
Persistent mal de debarquement syndrome: a motion-induced subjective disorder of balance.
Six patients with a distinct syndrome of persistent sensations of imbalance are presented. Common features included onset following a period of motion exposure, symptoms lasting months to years, mild unsteadiness and anxiety, minimal relief from antivertiginous medication, and normal neurologic and quantitative vestibulo-ocular examinations. One patient experienced recurrent episodes. Mal de debarquement refers to sensations of motion experienced on return to stable land after adaptation to motion lasting from hours to days in normal individuals. The presented patients exemplify a syndrome of persistent mal de debarquement. The entity is found in a relatively small number of dizzy patients. Persistent mal de debarquement is discussed in the context of what is known about long-term vestibulo-ocular adaptation to alterations of visual or vestibular environments.
Adult↗
Aging effects on auditory and vestibular responses: a longitudinal study.
PURPOSE: To identify age-related changes in the auditory and vestibular systems in normal older subjects followed serially over time. METHODS: Pure tone hearing levels, speech reception threshold, speech discrimination scores, and vestibulo-ocular responses were measured in 57 normal older subjects (mean age, 82) on 5 yearly examinations. RESULTS: There was a significant (P < .001) increase in pure tone threshold averages (about 1 dB per year) and speech reception threshold averages (about 2 dB per year), and a significant (P < .001) decrease in discrimination scores (about 2% per year) over the 5 years of follow-up. There was a significant (P < .05) amplitude-dependent decrease in gain and increase in phase lead of the vestibulo-ocular reflex and a significant (P < .01) decrease in gain of visual-vestibular responses at low frequency sinusoidal stimulation over the 5 examinations. Years 1 to 5 differences in individual subjects were significantly (P < .01) correlated across auditory and vestibular tests, but not between auditory and vestibular tests (P > .01). CONCLUSION: This is the first longitudinal study to show age-related decreases in auditory and vestibular responses in normal older subjects. Because the age-related changes in the auditory system were not correlated with age-related changes in the vestibular system, the 2 systems may age at different rates in the same individual. These changes likely result from degeneration in both peripheral and central structures, although age-related changes in the central nervous system probably are more important from a functional point of view.
Aged↗
Neurotology of migraine.
Neurotologic symptoms are common with migraine, yet relatively little is known about the pathophysiology of such symptoms. Motion sensitivity with bouts of motion sickness occurs in about two thirds of patients with migraine. Episodes of vertigo occur in about one fourth of patients and, in some, vertigo is the only symptom (so-called "migraine equivalent"). Phonophobia is the most common auditory symptom, but fluctuating hearing loss and acute permanent hearing loss occur in a small percentage. Migraine can mimic Meniere's disease and so-called "vestibular Meniere's disease" is usually associated with migraine. The recent discovery of a mutation in a brain calcium-channel gene in families with hemiplegic migraine and in families with episodic vertigo and ataxia suggests a possible mechanism for neurotologic symptoms in patients with more common varieties of migraine. A defective calcium channel, primarily expressed in the brain and inner ear, could lead to reversible hair cell depolarization and auditory and vestibular symptoms. This hypothesis is currently being investigated in other families with migraine headaches and neurotologic symptoms. Hopefully, such studies will lead to improved diagnosis and better treatments in the future.
Brain↗
Quantitative measurement of smooth pursuit eye movements.
Smooth pursuit eye movements were quantitatively assessed in 25 normal subjects and 22 patients. A laboratory digital computer was used to compute 200 eye velocity samples per second and to statistically compare these eye velocity measurements for five different object velocities. Of six statistics evaluated, mode eye velocity showed the least variability in normal subjects and was most frequently abnormal in patients. Compared to normal subjects, patients with brain stem degeneration and cerebellar-pontine angle tumors with brain stem compression had significant impairment of smooth pursuit. Patients with peripheral vestibular lesions and C-P angle tumors without brain stem compression did not have impaired smooth pursuit. These preliminary findings suggest that quantitative measurement of pursuit eye velocity can be a sensitive test for brain stem dysfunction.
Adult↗
Eye-tracking and optokinetic nystagmus. Results of quantitative testing in patients with well-defined nervous system lesions.
Eye-tracking and optokinetic nystagmus (OKN) abmormalities in patients with focal lesions of the nervous system are reviewed. Patients with peripheral labyrinthine lesions can have deficits in smooth pursuit and OKN, but they are rapidly compensated after an acute lesion. By contrast, patients with large, cerebellopontine angle tumors have progressive impairment of pursuit and OKN as the tumor enlarges. Abnormalities of saccadic eye movements suggest intrinsic central nervous system (CNS) dysfunction. Saccade accuracy is severely impaired with cerebellar lesions, while brain stem disease frequently results in a slowing of saccade maximum velocity. Smooth pursuit and OKN abnormalities are common with all types of CNS lesions. The pattern of eye-tracking and OKN abnormality can be useful in anatomically localizing nervous system lesions.
Atrophy↗
Caloric testing. 1. Effect of different conditions of ocular fixation.
Twelve normal subjects received standard caloric testing under the following conditions: 1) fixation, 2) Frenzel glasses in a dimly lit room, 3) eyes open in total darkness, and 4) eyes closed. Multiple nystagmus response parameters were evaluated and statistically compared for each condition. Fixation markedly diminished induced nystagmus and produced the largest coefficient of variation for each response parameter. Caloric testing with eyes closed resulted in periodic nystagmus suppression and a less distinct saw-toothed pattern. As with fixation, the coefficient of variation was consistently higher with eyes closed compared to eyes open in darkness or Frenzel glasses. It is concluded that caloric testing of the vestibulo-ocular reflex arc should be performed with eyes open in darkness or with Frenzel glasses.
Central Nervous System Diseases↗
Caloric testing 2. results in normal subjects.
A large number of variables were examined simultaneously for 43 normal subjects over the four irrigations of a caloric test. Care was used for every step of the testing procedure and data analysis to eliminate as much of the variance in the caloric responses as possible. The normality of each variable's distribution was examined using the Wilk-Shapiro W test and corrected if necessary by the best of several transformations. The means, standard deviation, and 95% confidence intervals of the resultant data were derived. Statistical tests of temperature, sidedness, and directionality were done on the variables and several important sources of variance were found and explained.
Electrooculography↗
Caloric testing. 3. Patients with peripheral and central vestibular lesions.
Results of bithermal caloric testing in 83 patients with unilateral peripheral vestibular disease, cerebellopontine angle tumors and vertebrobasilar insufficiency were compared in order to find which response measurements identified the most abnormal responses in each disease category. A laboratory digital computer was used to quantitatively assess each caloric response and a large digital computer was used to statistically compare 110 measurements generated from each caloric test. Of the commonly used response parameters maximum slow component velocity (SVMx) and sum of slow amplitudes (SSA) were most sensitive in each category and duration of response (TDUR) was least sensitive. This order was maintained for the vestibular paresis (VP), directional preponderance (DP) and temperature effect (TE) formulas. The magnitude of DP was significantly correlated with the magnitude of spontaneous vestibular nystagmus and both occurred with approximately the same frequency in peripheral and central disorders. There was no reliable way of separating end-organ from VIII nerve or peripheral from central disorders on the basis of the caloric responses.
Adolescent↗
Comparison of vestibular subjective sensation and nystagmus responses during computerized harmonic acceleration tests.
A comparison was made between the phase of vestibulo-ocular reflex (VOR) responses to sinusoidal rotatory tests and the phase of the subjective sensation (SS) to rotation. A parallelism was found between the results of both sets of data such that they behaved in accordance with the prediction of the pendulum model of vestibular function. The time constant of the VOR (17.5 seconds) was longer, however, than that of the SS (13 seconds). Measurements in patients with unilateral labyrinthine pathology also showed comparable changes in both responses. One group of patients with complete unilateral labyrinthine paralysis showed an advance of the phase of the VOR and of the SS. However, phase measurements in the group of patients with only partial unilateral labyrinthine paralysis were not significantly different statistically from those of normal subjects.
Caloric Tests↗