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At least 883 records · Page 49Linked to original sources
PubMed1992

[Nicardipine attenuates the sympathetic reflex of orthostatism: do dihydropyridine-sensitive calcium channels regulate noradrenaline release?].

Twelve hypertensive subjects were treated for 2 weeks with the dihydropyridine calcium channel antagonist nicardipine (40 mg daily) according to a double-blind, placebo-controlled study protocol. Nicardipine treatment significantly decreased systolic and diastolic blood pressure and increased plasma noradrenaline levels measured at supine rest. However, the treatment significantly inhibited the physiological increase of circulating neurotransmitter following sympathetic stimulation induced by orthostatism. These results suggest that dihydropyridine-sensitive calcium channels may modulate the noradrenaline release from nerve terminals of the peripheral sympathetic nervous system.

Adult↗
PubMed1999

Assessing otolith function by the subjective visual vertical.

The effects of peripheral vestibular diseases on the subjective visual vertical (SVV) are resumed and provide the basis for some insights into the otolith pathophysiology. With a normal range of 0 +/- 2 deg (when measured in an upright body position), the SVV was shifted by 11 +/- 6 deg toward the ipsilateral ear in 40 patients following an acute unilateral vestibular deafferentiation (UVD), but in the opposite direction in 9 of 52 patients after stapes surgery. These opposite effects suggest a push-pull mechanism of the pairs of otolith organs with respect to the SVV. The dissociation between the SVV and the perception of body position indicates influences by unconscious reflexive mechanisms such as ocular cyclotorsion on the SVV. In chronic UVD patients, lateral shifts of the subjects during constant angular velocity rotation into various eccentric positions (+/- 16 cm) revealed a shift of the "center of graviception" close to the remaining intact contralateral inner ear. To date, this seems to be the most consistent test for clinical identification of a chronic compensated unilateral loss of otolith function. The findings regarding asymmetries in otolithic sensitivity to medially and laterally directed roll-tilts remain controversial, probably mainly because of influences of extravestibular cues.

Afferent Pathways↗
PubMed1987

Cardiovascular reflexes in Parkinson's disease.

The autonomic nervous system (ANS) function of patients with Parkinson's disease (PD) was investigated in 30 patients with PD, and in 21 healthy subjects of similar age by utilizing cardiovascular reflex measurements as indicators. In deep breathing, in the Valsalva manoeuvre, and in the tilting test the heart rate variability (R-R variation) differed significantly between the patients and the controls: the beat-to-beat variation was clearly decreased in patients with PD. Responses in diastolic pressure to isometric work were also clearly diminished. However, no significant differences in any measured ANS indices were found between the patients who were treated with levodopa and those who were not. Similarly, anticholinergics did not seem to affect the results.

Adult↗
PubMedDate not supplied

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↗
PubMed1986

Receptive fields of motor neurons underlying local tactile reflexes in the locust.

The receptive fields of motor neurons to a hind leg were mapped by recording intracellularly from their cell bodies or from the muscle fibers they innervate while stimulating mechanoreceptors on the surface of that leg. Each motor neuron is affected by a specific array of receptors that make up its receptive field. Boundaries along the anteroposterior or dorsoventral axes of the leg divide the receptive fields into excitatory and inhibitory regions. Proximodistal boundaries may correspond to the articulations between parts of the leg. Motor neurons that innervate antagonistic muscles have complementary receptive fields, so that the region that is excitatory for one is inhibitory for the other. The receptive fields of the motor neurons overlap. Tactile stimulation therefore leads to a specific local reflex that involves the coordinated movement of the segments of a leg. Five local reflexes are described, each of which moves the leg away from the site of stimulation. Afferents from the external mechanoreceptors do not synapse directly on the motor neurons, but instead on spiking local interneurons, some of which then synapse directly on motor neurons. These local interneurons have smaller receptive fields delineated by the same boundaries, so that the receptive fields of the motor neurons can be constructed from appropriate combinations of them. It is suggested that receptive fields are organized as "functional maps" that are appropriate for particular behavioral responses rather than solely to preserve or refine spatial information.

Animals↗
PubMed1999

Vestibular disorders in primary thrombocytosis.

OBJECTIVE: Balance disturbances are some of the most common symptoms among the clinical manifestations of chronic myeloproliferative disorders (MPDs) with a high platelet count, such as essential thrombocythaemia (ET) and polycythaemia vera (PV). In this study, we evaluated the vestibulo-oculomotor and vestibulospinal reflexes in a group of patients suffering from these diseases. DESIGN: Evaluation of balance disturbances. SETTING: Department of Neurosciences, ENT Unit, University of Pisa, Italy. METHOD: In this study, we evaluated 43 patients suffering from ET and PV who underwent otoneurologic examination, based on a study of the vestibulo-oculomotor and vestibulospinal reflexes. RESULTS: There was exclusive central vestibular involvement in 26 cases (60.4%), peripheral and central signs were associated in 8 cases (18.6%), and the involvement was purely peripheral in 1 patient. In six patients (14%), the otoneurologic examination revealed no alterations. CONCLUSIONS: The high percentage of balance disorders in cases of ET and PV probably depends upon disorders of the microcirculation due to platelet dysfunction. We also postulate a full explanation of the involvement of the central vestibular system on the basis of a greater availability of central activated serotonin acting as neuromediator.

Adult↗
PubMed1977

The efficacy of the laryngeal reflex in conscious sedation.

The Jorgensen technique and nitrous oxide-oxygen sedation were evaluated for the risk of aspiration. Volunteers and patients were studied in the supine, semisupine, and Trendelenburg positions. Aspiration occurred in a single patient under the Jorgensen technique and could be related to the presence of a narcotic in the mixture. The incidence of tracheal soiling was lower than that with other intravenous techniques and could be attributed to the use of the semisupine position or the baseline concept of narcotic dosage in the Jorgensen technique. In the nitrous oxide-oxygen sedation technique, aspiration was not noted. The study suggests that use of a narcotic in an intravenous sedative technique increases the hazard of aspiration.

Adolescent↗
PubMed1990

Vestibular function in periodic alternating nystagmus.

The vestibulo-ocular reflex of 4 patients with periodic alternating nystagmus (PAN) was studied in detail. Rotational testing was used to investigate the horizontal semicircular canal-ocular reflex, canal-otolith interaction, and the dynamic otolith-ocular reflex. Results indicated abnormal gain and phase of the horizontal semicircular canal-ocular reflex during sinusoidal rotation and a variable rate of decay of postrotatory responses. Each patient had abnormal canal-otolith interaction. An enlarged modulation component of the dynamic otolith-ocular response was observed in each patient. This study supports the idea that PAN is caused by an instability in the velocity storage element, a hypothetical neural circuit that perseverates the eye movement response to both vestibular and optokinetic stimulation. Further, we postulate that PAN may be caused by lesions of the cerebellar uvula and nodulus or their connections with the brainstem vestibular nuclei.

Adult↗
PubMedDate not supplied

Dysautonomia in Parkinson's disease: relationship to motor disability.

Disturbances of autonomic nervous system functions are common in patients with Parkinson's disease (PD) and may develop as a result of pathology in centers of autonomic regulation such as the hypothalamus, brainstem, and sympathetic ganglia. We examined the relationship between the degree of motor disability, as determined from the Hoehn and Yahr scale (1967), and the presence of pandysautonomia, as determined by the assessment of noninvasive cardiovascular reflexes, in 29 unmedicated PD patients (mean age: 72.0 years, SD = 8.9). In addition, we investigated the relationship of pandysautonomia to CT scan measures of cerebral atrophy and to the presence or absence of pineal calcification. Nine patients (31.0%) were found to have pandysautonomia with deficits in both sympathetic and parasympathetic cardiovascular functions. Pandysautonomia was statistically related only to the degree of motor disability (p < .01). These findings demonstrate a significant association between motor disability and objective impairment of central cardiovascular functions in PD.

Aged↗
PubMedDate not supplied

Three-dimensional characteristics of rhesus monkey vestibular nystagmus after velocity steps.

In rhesus monkeys we have investigated 3-dimensional orientations of angular eye velocity vectors during vestibular step responses about an earth-vertical axis. Monkey body position with respect to the rotation axis was systematically changed between upright, 90 degrees ear-down, and supine positions to induce oblique eye movements with horizontal, vertical, and torsional components, respectively. Angular eye velocity axes deviated from stimulus axes due to two types of anisotropies in the vestibulo-ocular reflex, that is, gain anisotropy and velocity-storage anisotropy. Deviations of eye velocity vectors from stimulation axes at peak slow-phase velocity could well be predicted by vectorial summation of gains obtained for the cardinal directions (horizontal, vertical, and torsional). During nystagmus decay, time constants after oblique velocity steps showed a tendency to be similar in participating components. However, this adjustment of time constants was incomplete for horizontal-torsional and horizontal-vertical-down vestibular responses, leading to an orientation change of eye rotation axes during slow-phase velocity decay with a bias toward the horizontal eye movement component.

Animals↗
PubMed1993

Dynamic visual acuity of normal subjects during vertical optotype and head motion.

PURPOSE: To characterize the effect of passive vertical head motion on dynamic visual acuity of young, normally sighted subjects wearing telescopic spectacles, and to relate this to the velocity of images on the retina. METHODS: Static visual acuity was measured without motion. Dynamic visual acuity was measured during vertical, sinusoidal motion of either optotypes or of a servo-driven rotating chair in which subjects were seated. Dynamic visual acuity for head motion was measured unaided, as well as with 1.9X, 4X, and 6X telescopic spectacles. Vertical eye movements were recorded using magnetic search coils. RESULTS: During optotype motion, acuity declined with increasing velocity to a minimum of approximately 20/200 at 100 degrees/sec. Pursuit gain (eye velocity/optotype velocity) for moving optotypes was low except for optotype velocities of 20 degrees/sec of less. Dynamic visual acuity without telescopic spectacles was not sensitive to head motion. Static visual acuity improved with increasing telescopic spectacle power, but dynamic visual acuity became progressively impaired by head motion as telescopic spectacle power was increased. Compared with static visual acuity, head motion with peak velocity of 40 degrees/sec reduced acuity two-fold for 1.9X telescopic spectacles, fourfold for 4X telescopic spectacles, and eightfold for 6X telescopic spectacles. Visual vestibulo-ocular reflex gain with telescopic spectacles increased to values markedly above 1.0, but was always less than telescopic spectacle magnification. There was visual tolerance of slip velocities of 2 degrees/sec or less, above which acuity declined in proportion to the 0.6 power of retinal slip velocity. Above 2 degrees/sec, retinal slip velocity accounted for 95% of the variance in dynamic visual acuity. CONCLUSIONS: These results confirm that acuity is sensitive to retinal image motion in the vertical direction, and extend this finding to indicate that sensitivity of acuity to vertical head motion during wearing of telescopic spectacles is attributable to retinal image slip velocity.

Adult↗
PubMedDate not supplied

Tilt suppression of vestibulo-ocular reflex in patients with cerebellar lesions.

The effect of tilt on the time constant of post-rotatory nystagmus was determined in a group of normal subjects and patients with cerebellar lesions. The normal subjects showed a vestibular response that decayed with a time constant of 19.6 s when upright and 7.2 s after tilt prone. Patients with midline cerebellar lesions near the uvula and nodulus had time constants that were normal in the upright position but were unaffected by head tilt. Patients with cerebellar lesions due to the Arnold-Chiari malformation showed behavior that was intermediate between that of normal subjects and the patients with midline lesions. These results provide evidence that in humans, the midline cerebellum regulates a neural network in the brainstem that perseverates peripheral vestibular input.

Adolescent↗
PubMed1991

[Experimental research on vestibular compensation using posturography].

Vestibular compensation is a representation of nervous system plasticity which manifests as a gradual recovery of equilibrium function both in vestibulo-spinal system and vestibulo-oculomotor system. In order to assess whether the vestibular compensation is a homogeneous process among the different reflexes, the Authors have studied two groups of subjects affected by peripheral or central lesion. The development of the vestibular compensation has been evaluated by the rotation and posturographic tests. The results demonstrate a constant correlation between rotation and stabilometric parameters in the patients suffering from peripheral dizziness while there isn't any correlation between acceleratory and posturographic tests in patients affected by central vertigo. These results demonstrate that the compensation develops at the different levels of the balance function in a very different and independent way and that comparison of the rotation and posturographic patterns may be useful to establish the peripheral or central site of the lesions.

Adult↗
PubMed1979

Cervical and vestibular afferent control of oculomotor response in man.

Oculomotor response in the absence of vision has been compared in a group of 12 normal humans in two experimental conditions testing (a) the vestibulocular reflex by whole-body oscillation on a turntable, and (b) the cervico-ocular reflex by oscillation of the body with the head held stationary. The stimulus was a sinusoidal oscillation (peak angular velocity +/- 50 degrees/sec) at frequencies between 0.2 and 1.3 Hz. The slow-phase eye movements of the vestibulo-ocular response were compensatory for head movement and showed a mean gain of 0.54--0.90, increasing with frequency. The cervicoocular response was found to be very variable. The slow-phase eye movements were of low velocity (mean gain 0.05) and did not generally compensate for body movement. During neck torsion, some subjects exhibited large overall eye deviations composed of both slow and fast phase eye movements.

Eye Movements↗
PubMed1995

Off-axis rotation as a test of otolith function.

This experiment was performed to determine whether linear acceleration causes a change in the vestibulo-linear reflex (VOR) that could be exploited as a research and/or clinical test of otolith function. The effect of otolith stimulation on the VOR was studied in the horizontal and vertical planes in 10 cats. The VOR was induced by pulses of angular acceleration (velocity ramps). During some of the test runs, a centripetal linear acceleration stimulus was also applied to stimulate the otolith organs. Using the stimuli combination as tested in this project, the authors found that otolith stimulation affected the vertical VOR but not the horizontal VOR. The vertical VOR was asymmetric. While the methods used in this study are useful and the equipment requirements make these techniques generally impractical for clinical testing.

Acceleration↗
PubMed1997

Deviation of the subjective vertical in long-standing unilateral vestibular loss.

We evaluated changes in the subjectively perceived gravitational vertical as an index of imbalance in the function of the right and left otolith organs. In addition to normal subjects (n = 25), we measured patients with a longstanding (mean 4.5 year +/- 3.2 SD; range 0.5-11.5 years) unilateral vestibular loss after surgery for acoustic neuroma (n = 32), patients with partial unilateral vestibular loss (n = 7) and patients with bilateral vestibular hyporeflexia (n = 8). Normal subjects could accurately align a vertical luminous bar to the gravitational vertical in an otherwise completely dark room (mean setting -0.14 degree +/- 1.11 SD). Patients with left-sided (complete; n = 13) or right-sided (complete; n = 19 and partial; n = 7) unilateral vestibular loss made mean angular settings at 2.55 degrees +/- 1.57 (SD) leftward and 2.22 degrees (+/-1.96 SD) rightward, respectively. These means differed highly significantly from the normal mean (p < 0.00001). In the time interval investigated (0.5-11.5 years) the magnitude of the tilt angle showed no correlation with the time elapsed since the operation. The mean setting by patients with clinically bilateral vestibular loss (-1.17 degrees +/- 1.96 SD; n = 8) did not significantly differ from the control group. The systematic tilts of the subjective vertical in patients with a unilateral vestibular impairment were correlated with their imbalance in canal-ocular reflexes, as reflected by drift during head-oscillation at 2 Hz (r2 = 0.44) and asymmetries in VOR-gain for head-steps (r2 = 0.48-0.67). These correlations were largely determined, by the signs of the asymmetries; correlation between the absolute values of the VOR gain asymmetries and subjective vertical angles proved to be virtually absent. We conclude that the setting of the subjective vertical is a very sensitive tool in detecting a left-right imbalance in otolith function, and that small but significant deviations towards the defective side may persist for many years (probably permanently) after unilateral lesions of the labyrinth or the vestibular nerve.

Ear, Inner↗
PubMed1992

Three-dimensional head angular velocity detection from otolith afferent signals.

Afferent signals from the otolith organs can produce compensatory eye position and velocity signals which has been described as linear vestibulo-ocular reflex (LVOR). The afferent otolith signals carry information about head orientation and changes of head orientation relative to gravity. A head orientation (tilt) related position signal can be obtained from population vector coding of tonic otolith afferent signals during static or dynamic head tilts, which in turn could produce compensatory eye position signals in the LVOR. On the other hand, eye angular velocity signals may be extracted, as proposed in this study, from the population response of tilt-velocity sensitive otolith afferents. Such afferents are shown to encode instantaneous head orientation relative to gravity at onset of a head movement and, as the movement continues, the projection of head angular velocity onto the earth-horizontal plane, indicating the instantaneous direction of movement relative to gravity. Angular velocity components along the earth-vertical direction which are not directly encoded by otolith afferents can be detected by central signal processing. Central reconstruction of 3D head angular velocity allows to obtain information about absolute head orientation in space even in the absence of semi-circular canal related information. Such information is important for generating compensatory eye movements as well as for dynamic control of posture.

Afferent Pathways↗
PubMed1998

Longitudinal follow-up of cardiovascular reflex tests in multiple sclerosis.

Several studies have shown various degrees of autonomic dysfunction in patients with multiple sclerosis. Longitudinal follow-up studies are remarkably scarce up to now. We assessed autonomic dysfunction twice with an interval of 1 year in 20 relapsing remitting and 26 secondary progressive MS-patients. Autonomic function was assessed by the heart rate response during deep breathing, standing up and Valsalva manoeuvre. Only the maximum change in heart rate after standing up (in ms and beats/min) and the Max/Min ratio after standing up showed significant worsening over 1 year. The changes in EDSS scores also documented gradual deterioration of the neurological condition over the study period. We conclude that there is progression of autonomic dysfunction in MS over 1 year and that this could correlate with progression in clinical disability.

Adult↗