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Biomedical subjects

V Honrubia

Publications and source records attributed to V Honrubia.

At least 199 records · Page 11Linked to original sources
PubMedDate not supplied

Evaluation of multiple-frequency rotatory testing in patients with peripheral labyrinthine weakness.

Multiple-frequency rotatory testing was performed in a series of 12 normal subjects and 27 patients who had significant labyrinthine paralysis. Fourteen of the patients had total loss of labyrinthine function. Phase leads of the responses were much greater in the lower-frequency measurements and measured gains of the responses to ampullopetal stimulation were qualitatively greater than those of the responses to ampullofugal stimulation. However, many patients' responses continued to fall within the normal range because of the large variability of the responses of normal subjects. The value of rotatory testing in clinical diagnosis is discussed.

Caloric Tests↗
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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↗
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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↗
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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↗
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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↗
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Evoked responses from peripheral stimulation of the facial nerve.

Evoked responses to electrical stimulation of the facial nerve were recorded in dogs with vertex electrodes placed both inside and outside the skull. Three waveforms were recorded. The first two waveforms appeared to be related to electrical activity carried by antidromic propagation within fibers of the facial nerve. The third waveform appeared to be caused by the muscular response that occurred as a result of orthograde conduction in the nerve. The effects of changing the stimulation site, voltage, duration, and frequency were recorded. It appears that, by means of far-field techniques, it is possible to reliably record evoked responses that reflect antigrade conduction via fibers of the facial nerve.

Animals↗
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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↗
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Arrangement of vestibular nerve fibers in the semicircular canal crista of the chinchilla.

The topographic arrangement of vestibular nerve fibers innervating semicircular canal cristae of the chinchilla was studied using computer-aided video-microscopy and three-dimensional reconstruction. At the level 20 microns proximal to the base of the crista, bundles consisting of 30-50 nerve fibers each were identified. Nerve fibers in bundles were classified into seven categories depending on the diameter. We confirmed that large nerve fibers were more frequently found in the central bundles and small nerve fibers were more frequently found in the peripheral bundles. The central bundle might function as a physiological unit coding various types of head movements, whereas the peripheral bundle might contribute more to the detection of slow and long-lasting movements giving rise to tonus and posture changes. The canalicular nerve may code rotational acceleration of the head via function- and locus-specific nerve fiber bundles.

Animals↗
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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↗
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Physiological basis of cochlear transduction and sensitivity.

Experiments were conducted in the guinea pig cochlea and the Xenopus laevis lateral line organ to obtain information about the electrical impedance properties of the cochlea, the sources and characteristics of the cochlear potentials, and to determine if hair cells are electrically excitable. The significance of the resting and evoked cochlear potentials in the transduction process leading to excitation of the acoustic nerve fibers was evaluated by comparing the results of electrophysiological experiments with the prediction of a model of the cochlea designed after the mechanoelectric theory of hair cell function. The results of these experiments 1) were compatible with the prediction of the mechoelectric theory of cochlear function; 2) made it possible to estimate and compare the energy dissipated in generating and maintaining the cochlear potentials with the stores of biochemical energy available in the cochlea; and 3) showed that the hair cells are electrically excitable, from which it was concluded that interaction between the hair cells is feasible.

Animals↗
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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↗
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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↗
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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↗
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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↗
PubMedDate not supplied

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↗
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A new method for determining impulsive time constants and their application to clinical data.

We have developed an accurate, convenient method for determining unique values of vestibular time constants from impulsive tests. The method was used to determine the mean values and standard deviations of 36 normal subjects. A comparison between these normal values and data from patients with cerebellopontine (CP) angle tumors or unilateral peripheral vestibular lesions showed no significant difference in the values of the time constants. We conclude that shape-descriptive parameters such as time constants cannot differentiate between subjects and patients.

Adaptation, Physiological↗
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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↗