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At least 523 records · Page 29Linked to original sources
PubMedDate not supplied

Neuroanatomical correlates of vestibular function.

Neuroanatomical data revealed by new neuroanatomical techniques over the past decade, have clarified the central connections of the peripheral vestibular sense organs. A knowledge of this information is important in the clinical evaluation of vestibular disorders. The reflex connections of the semicircular canals serve vestibulocerebellar, vestibulo-ocular, commisural, and vestibulospinal pathways. The central connections of the utricular macula are primarily in a descending direction to the motor neurons of the entire length of the spinal cord. These form the basif for vestibulospinal reflexes which are characteristically associated with utricular function. Additional central connections provide the basis for vestibulo-ocular responses to utricular activity. Finally, the saccule has reflex connections both to the upper spinal cord to a minor degree and to extraocular nuclei that serve vertical and oblique eye movements. The minor vestibular group Y nucleus provides a commissural reflex connection for the saccule.

Acoustic Maculae↗
PubMedDate not supplied

Implications of Ewald's second law for evaluation of vestibular function.

The significance of Ewald's second law in the evaluation of the vestibulo-ocular reflex (VOR) was investigated using the transfer characteristics of the vestibular and VOR systems in normal rabbits and rabbits in which one horizontal semicircular canal had been blocked. The transfer characteristics of the vestibular system were derived from the experimental results reported by Goldberg and Fernández in 1971. A comparison was made of the properties of the bilateral and monolateral VOR systems with the predictions of a piecewise linear model of the vestibular system. The data received quantitatively collaborate the prediction of Ewald's second law as it applies to the VOR responses.

Animals↗
PubMed1988

Unilateral loss of peripheral vestibular function in patients: degree of compensation and factors causing decompensation.

Unilateral surgical ablation of peripheral vestibular function has been suggested for the treatment of a number of diseases that involve vestibular dysfunction. The postoperative distressing symptoms usually subside with time, whereupon the patient is said to have clinically compensated. However, even in well-compensated patients, the initial symptoms may reappear--under certain conditions that are briefly discussed (decompensation)--and, in addition, vestibular gaze stabilization deficits, (apparently permanent) appear whenever moderately rapid head movements are imposed. Thus, surgical ablation of unilateral peripheral vestibular function should not be considered "a treatment of choice," and should be performed in only carefully selected cases.

Animals↗
PubMed1990

Free amino acid analysis of guinea pig perilymph: a possible clinical assay for the PLF enigma?

Controversy prevails regarding the accuracy of the clinical diagnosis of perilymphatic fistula (PLF). The diagnosis of PLF has been based on the subjective evaluation of vestibular function tests and the intraoperative macroscopic visualization of "clear fluid" from the oval/round windows at the time of exploratory tympanotomy. However, the subjective visual characterization of PLF varies among observing surgeons. Furthermore, perilymph can be "contaminated" with serum, blood, cerebrospinal fluid (CSF), and local anesthesia. This article presents a scientific biochemical microassay for the free amino acid profile of perilymph. Microaliquots of uncontaminated perilymph were sampled from the bilateral round windows (scala tympani) of 20 guinea pigs and analyzed for 19 free amino acid concentrations (FAAC) by high-performance liquid chromatography (HPLC). These samples were compared with the FAAC of guinea pig serum samples. Perfect predictor value ranges were nonoverlapping for 12 of 19 free amino acids in perilymph vs. plasma. Amino acid microassay of middle ear fluid for verification of "true" perilymph vs. nonperilymph fluids by the identification of nonoverlapping FAA markers may allow scientific verification of the existence of PLF in "suspected" patients.

Amino Acids↗
PubMed1993

Bilateral vestibular neurectomy for treatment of vertigo.

The effects of bilateral vestibular neurectomy on equilibrium and vestibular function were clinically evaluated in two patients more than 15 years after surgery. Both patients had bilateral Menière's disease and their vertiginous spells were permanently resolved after the second vestibular neurectomy. Symptoms of disequilibrium were absent in one patient and mild in the other. Reflexive horizontal eye movements on whole body rotation in darkness were absent on low angular accelerations (2 degrees/s2), but could be elicited with angular accelerations of 20 degrees/s2 or higher. Extravestibular cues generating these eye movements seemed to be unlikely because a "control" patient with complete peripheral vestibular ablation after bilateral subtotal petrosectomy did not present reflexive eye movements under the same stimulus paradigms. An incomplete deafferentiation of the vestibular end organ (rather than regeneration of vestibular nerve fibers) and a consecutive impairment of the central velocity storage mechanism may explain the good functional outcome in our bilateral neurectomized patients.

Activities of Daily Living↗
PubMed1997

Clinical-pathologic correlation in a patient with selective loss of hair cells in the vestibular endorgans.

We found a selective loss of vestibular hair cells in a patient followed for more than 10 years with imbalance and oscillopsia due to idiopathic progressive loss of vestibular function. Hearing function and cochlear hair cells were normal. The vestibulo-ocular reflex (VOR) gain at high frequencies was relatively maintained despite marked shortening of the dominant VOR time constant (to less than 500 ms). Ultrastructural examination of remaining hair cells showed mitochondrial abnormalities. The ultrashort VOR time constant probably resulted from changes in firing patterns of the primary afferent nerves due to loss of hair cells and impaired energy metabolism in remaining hair cells.

Adult↗
PubMed1998

Disequilibrium in older people: a prospective study.

OBJECTIVE: To identify the clinical and neuroimaging features in older people with disequilibrium of unknown cause. BACKGROUND: Many older people show a deterioration of balance without an identifiable cause. Whether the disequilibrium is a normal aging phenomenon, the result of yet unidentified neuropathology, or a combination of the two is unknown. METHODS: Twenty-nine patients who complained of disequilibrium (ages 75 to 92) and 29 age- and sex-matched control subjects completed five yearly examinations including history and semiquantitative neurologic examination, activities of daily living, visual acuity, mini-mental status, bedside gait and balance score (Tinetti), Purdue pegboard, and vestibular function testing. Concerns about falling and number of falls were quantified. Subcortical white matter lesions (WML) and frontal atrophy (FA) were graded (blindly), and the ventricular-brain ratio (VBR) was measured from MRIs of the brain. RESULTS: On entry, patients differed from control subjects only in measures of balance, concerns about falling, and falls. Over the 5 years, patients were four times more likely to fall than control subjects. The number of falls was highly correlated with measures of balance (p < 0.001). The VBR as well as the frequency of WML and FA were all significantly (p < 0.001) greater in patients than in control subjects. CONCLUSION: Disequilibrium of unknown cause in older people is associated with frequent falls, concerns about falling, brain atrophy, and WML on MRI. Some cases are probably caused by small-vessel ischemic disease.

Accidental Falls↗