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Biomedical subjects

R W Baloh

Publications and source records attributed to R W Baloh.

247 records · Page 14Linked to original sources
PubMedDate not supplied

Implications of Ewald's second law for diagnosis of unilateral labyrinthine paralysis.

The feasibility of replacement of the caloric test with sinusoidal rotatory stimulations of differing frequencies was investigated in ten normal subjects and seven patients with unilateral labyrinthine paralysis. Testing was performed at frequencies ranging from 0.0125 to 0.2 Hz at 60 degrees/sec and at 0.05 Hz at peak velocities of 30 degrees/sec to 180 degrees/sec. Gain, phase, and asymmetry of the nystagmic responses were measured in these groups. Results indicated that the rotatory test was not reliable enough to be used as the sole measure for identifying patients with unilateral labyrinthine lesions.

Analog-Digital Conversion↗
PubMedDate not supplied

Ewald's second law re-evaluated.

Patients and experimental animals (cats) with one functioning horizontal semicircular canal were tested with precise rotatory stimuli. Nystagmus responses were quantified with EOG and a laboratory digital computer. After large-magnitude stimuli there was a statistically significant difference between the maximum slow component velocity of nystagmus induced by ampullopetal endolymph flow and that induced by ampullofugal endolymph flow in all patients and cats.

Animals↗
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Voluntary control of the human vestibulo-ocular reflex.

The ability of normal subjects to increase their vestibulo-ocular reflex (VOR) gain with an imagined stationary frame of reference was dependent on their strategy and the test conditions. With large amplitude sinusoidal rotation (greater than 50 degrees) subjects could not increase their VOR gain regardless of the strategy used. With small amplitude excursions (less than 50 degrees) they could significantly increase their VOR gain if they used a 'single stripe' strategy. Accompanying this increase in VOR gain was an increase in the phase lead of VOR slow phase velocity relative to head velocity. Apparently the signal used to augment the VOR gain with an imagined stationary surround had phase characteristics similar to those of primary vestibular afferent neurons.

Eye Movements↗
PubMedDate not supplied

Eye movement abnormalities in a family with cerebellar vermian atrophy.

We report the oculographic findings in a family whose members have a dominantly inherited, early onset, non-progressive syndrome which includes spontaneous upbeating nystagmus and mild cerebellar ataxia associated with cerebellar vermian atrophy seen on magnetic resonance scanning. Eye movements recorded with electro-oculography and a magnetic scleral search coil revealed severely impaired horizontal and vertical smooth pursuit, optokinetic nystagmus and visual-vestibular interaction, symmetrical horizontal but asymmetrical vertical vestibulo-ocular reflex, and normal saccades. The midline cerebellum appears to be essential for both horizontal and vertical visual tracking and visual modification of the vestibulo-ocular reflex in man.

Adult↗
PubMedDate not supplied

The impulsive test in man.

The impulsive test is brief and comfortable to the patient. The SVM is the best discriminator of the variables examined. By using percent differences between CW and CCW responses in the same subject at the same stimulus magnitude, we can define a range for the normal population and indicate patients outside that normal range. The impulsive test gives directional information in patients with unilateral lesions. In patients with severe bilateral loss of vestibular function, measurable responses are still obtainable; while in patients with primary cerebellar disease, responses are increased. The test may also be useful in giving anatomic information about posterior fossa lesions.

Brain Neoplasms↗
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Age-related change of the neuronal number in the human medial vestibular nucleus: a stereological investigation.

An unbiased stereological method was used to assess the effect of aging on the number of neurons in the human medial vestibular nucleus. We studied 13 normal brainstem specimens (age at death from 40 to 93 years) that were part of a prior study that counted neuronal profiles and used a correction factor to estimate the number of neurons in the human vestibular nucleus. On average, we found 151.10(3) (CV = 0.15) neurons in the medial vestibular nucleus, which is 18% more than that in the prior study. Regression analysis showed a significant decrease in the number of neurons with aging. This age-related neuronal loss in the vestibular nucleus could have important functional implications regarding the well-known deterioration in balance that occurs with aging.

Adult↗
PubMedDate not supplied

Vertical optokinetic nystagmus and optokinetic afternystagmus in humans.

Vertical optokinetic nystagmus (OKN) and optokinetic afternystagmus (OKAN) were recorded in 6 normal subjects using the magnetic scleral search coil technique in order to reevaluate the up-down symmetry of these responses. The effects of body position relative to gravity were investigated by comparing OKN and OKAN elicited with the subjects in an erect and in a lateral side position. No consistent up-down asymmetry in vertical OKN was found but OKAN was asymmetric (up slow phase velocity > down slow phase velocity). Most subjects had an immediate reversal in OKAN slow phase velocity after downward stimuli. No significant effects of static head position (upright versus lateral position) on vertical OKN and OKAN were found. These features of human OKAN can be explained by the summation of two oppositely directed velocity storage mechanisms.

Adult↗
PubMedDate not supplied

Recent advances in clinical neurotology.

In recent years, owing to significant technological developments and an increased number of investigators entering the field, there have been spectacular advances in our understanding of the basic anatomy and physiology of the vestibular system. Unfortunately, these advances in basic science are slow to impact the clinical management of patients. We have selected a few important advances in clinical neurotology that have impacted the diagnosis and treatment of patients with vestibular disorders. This material was originally presented at the "Mechanisms of Vestibular Function and Dysfunction" symposium of the 1994 Neural Control of Movement meeting in Waikoloa, Hawaii.

Humans↗
PubMedDate not supplied

The linear vestibulo-ocular reflex in normal subjects and patients with vestibular and cerebellar lesions.

We measured the horizontal linear vestibulo-ocular reflex (LVOR) in normal human subjects and patients with abnormal angular vestibulo-ocular reflexes (AVOR) and abnormal smooth pursuit. Eye movements were induced by sinusoidal linear acceleration along the interaural axis (0.8 Hz, 0.5 g peak acceleration) on a parallel swing. Horizontal movement of each eye was recorded with an infrared limbus tracking device. Normal subjects increased LVOR sensitivity as real or imagined targets moved closer. Perceived target distance was more important than the vergence angle since changing the vergence angle alone with prisms resulted in only a slight change in LVOR sensitivity. Subjects suppressed the LVOR with real or imagined head-fixed targets. Patients with decreased horizontal AVOR responses had decreased horizontal LVOR responses with imagined earth-fixed targets in the dark. They were able to generate normal velocity LVOR responses with real earth-fixed targets. Patients with increased AVOR responses and poor smooth pursuit due to cerebellar atrophy had low LVOR responses that were minimally affected by real or imagined earth-fixed or head-fixed targets. We conclude that the smooth pursuit system and the cerebellum are critical for generating the eye movements required as subjects fixate a near target during translational head movements.

Adult↗
PubMedDate not supplied

Aging and the human vestibular nucleus.

Degenerative changes during aging have been identified in the inner ear and in the vestibular nerve, but not in the human vestibular nuclear complex (VNC). Therefore, the purpose of this study was to document quantitative morphometric changes within the VNC in humans as a function of age. The VNC of normal human subjects was examined for age-related changes using computer-based microscopy. Neuronal counts, nuclear volume, neuronal density, and nuclear length of the 4 vestibular nuclei were determined in 15 normal people, age 40 to 93 years. Based on a linear model, there was approximately a 3% neuronal loss per decade from age forty to ninety. VNC volume and neuronal density also decreased significantly with age, although to a lesser degree than did the number of neurons. Neuronal loss as a percentage of the total number of neurons was greatest in the superior vestibular nucleus and least in the medial vestibular nucleus. Despite the overall loss of neurons, the number of giant neurons (> 500 microns2) increased in older people. This increase in giant neurons could be traced to the accumulation of lipofuscin deposits in the cell somata. The overall rate of neuronal loss with aging in the VNC is comparable to that previously observed in hair cells, primary vestibular neurons, and cerebellar Purkinje cells, but is in contrast to prior reports of no age-related loss of neurons in other brain stem nuclei.

Adult↗