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PubMedDate not supplied

Initial and delayed circulatory responses to orthostatic stress in normal humans and in subjects with orthostatic intolerance.

Gravitational stresses, which are common daily event for humans, result in a diminution in central blood volume, due to displacement of blood to the lower parts of the body. They demand complex adjustments in the cardiovascular system to offset the decrease in cardiac filling pressure. Such changes are necessary to sustain arterial blood pressure at an appropriate level so that there is adequate perfusion of vital organs, especially the brain. These adjustments must compensate for both the initial and sustained orthostatic stress. The rapid short-term adaptations are mediated primarily by the cardiovascular reflexes with humoral agents reinforcing these reflexes during severe and prolonged orthostatic stress. Understanding these complex reflex adjustments in normal humans is necessary in order to appreciate subjects with orthostatic intolerance.

Atrial Natriuretic Factor↗
PubMedDate not supplied

[Comparative evaluation of the Fitzgerald-Hallpike caloric test and the monothermal Torok test in lesions of the cerebellar hemispheres].

The Fitzgerald-Hallpike caloric test and the monothermal Torok test were done in 58 patients with damage to the cerebellar hemispheres. In the Fitzgerald-Hallpike test symmetric vestibular reactions were obtained in 79.3% of cases. In the monothermal test vestibular decruitment of only type I and II according to Torok was demonstrated in 68.9% of all cases. This suggests that Torok test may be of great value in the diagnosis of damage to the cerebellar hemispheres. In the light of these results the author concludes that cerebellar hemispheres are responsible for stabilization of vestibulo-ocular reflexes and regulate the adequacy of the vestibulo-ocular responses in relation to the stimulus.

Adolescent↗
PubMed2001

Adaptive motor control in crayfish.

This article reviews the principles that rule the organization of motor commands that have been described over the past five decades in crayfish. The adaptation of motor behaviors requires the integration of sensory cues into the motor command. The respective roles of central neural networks and sensory feedback are presented in the order of increasing complexity. The simplest circuits described are those involved in the control of a single joint during posture (negative feedback-resistance reflex) and movement (modulation of sensory feedback and reversal of the reflex into an assistance reflex). More complex integration is required to solve problems of coordination of joint movements in a pluri-segmental appendage, and coordination of different limbs and different motor systems. In addition, beyond the question of mechanical fitting, the motor command must be appropriate to the behavioral context. Therefore, sensory information is used also to select adequate motor programs. A last aspect of adaptability concerns the possibility of neural networks to change their properties either temporarily (such on-line modulation exerted, for example, by presynaptic mechanisms) or more permanently (such as plastic changes that modify the synaptic efficacy). Finally, the question of how "automatic" local component networks are controlled by descending pathways, in order to achieve behaviors, is discussed.

Adaptation, Physiological↗
PubMed2006

Modulation of muscle sympathetic bursts by sinusoidal galvanic vestibular stimulation in human subjects.

There is controversy as to whether the vestibulosympathetic reflexes demonstrated in experimental animals actually exist in human subjects. While head-down neck flexion and off-vertical axis rotation can increase muscle sympathetic nerve activity (MSNA) in awake subjects, we recently showed that bipolar galvanic vestibular stimulation (GVS) does not. However, it is possible that our stimuli (2 mA, 1 s)-although capable of causing strong postural and occulomotor responses-were too brief. To address this issue we activated vestibular afferents using continuous sinusoidal (0.5-0.8 Hz, 60-100 cycles, +/-2 mA) bipolar binaural GVS in 11 seated subjects. Sinusoidal GVS evoked robust vestibular illusions of "rocking in a boat" or "swinging from side to side." Cross-correlation analysis revealed a cyclic modulation of MSNA ranging from 31 to 86% across subjects (mean +/- SE 58 +/- 5%), with total MSNA increasing by 156 +/- 19% (P = 0.001). Furthermore, we documented de novo synthesis of sympathetic bursts that were coupled to the sinusoidal input, such that two bursts-rather than the obligatory single burst-could be generated within a cardiac interval. This demonstrates that the human vestibular apparatus exerts a potent facilitatory influence on MSNA that potentially operates independently of the baroreceptor system.

Action Potentials↗
PubMed1979

Alteration of plasma ketamine levels in mice by probenecid.

Probenecid increases plasma ketamine levels in mice concurrently with an enhancement of duration of loss of righting reflex. The magnitude of these changes is directly related to the dose of ketamine and intervals between administration of compounds. Plasma levels of anesthetic are similar for all animals upon termination of hypnosis.

Animals↗
PubMed1990

The postnatal development of the air-righting reaction in albino rats. Quantitative analysis of normal development and the effect of preventing neck-torso and torso-pelvis rotations.

The aim of this study was to describe the ontogenesis of the air-righting reaction (ARR) in rats. The first experiment was performed on 6 newborn albino rats of both sexes and followed the development of the ARR over postnatal days 1-21. The degree of rotation achieved after falling from different heights was quantified according to a rating scheme. It appeared that the air-righting reaction is effected by a spiral movement which spreads in a cranio-caudal direction. The reaction develops between postnatal day 8 and 18. On postnatal day 10 only a few animals are able to turn their heads, this being possible only from a falling height of 60 cm and corresponding to a falling time of 350 ms. A rapid development of the reaction was found between days 10 and 14. The second experiment on 8 rats involved the use of immobilization in order to isolate the mechanisms that trigger the ARR. The immobilization prevented neck-torso rotation, torso-pelvis rotation, and both rotations in different animals. Despite the disruption of important (afferent) feedback systems, the reaction developed within the same age period as in control rats. Thus, the Magnus "chain reflex hypothesis' as basis for the ARR is rejected in favor of a central motor program hypothesis.

Age Factors↗
PubMed1997

[Carving and ski technique--aspects of biological regulation].

Based on theoretical calculations the effects of skis with great sidecuts on the biological regulation are shown. Of main interest is the overload of the biological system by unexpectedly catching an edge. The calculations show that a great sidecut using the same edge ankle causes a greater lateral deviation compared to a normal ski. The correction of unexpected incidents is done by reflex mechanisms. Remarkable consequences for the reflex time can be calculated for the various sidecuts only. It can be concluded that problems in using carving skis mainly occur in combining high velocities and/or weak movement experiences.

Acceleration↗
PubMed1994

Modulation of the triceps surae H-reflex with training.

Thirteen neurologically healthy adults were asked to balance on a specially designed balance board. This board allowed rotation in the sagittal plane only. Muscle activity of the triceps surae and tibialis anterior was sampled at 2 kHz and recorded. When the subject was balanced, soleus H-reflexes were elicited in the right leg with a constant-current stimulus pulse. The peak to peak amplitude of the soleus H-reflex served as the perturbation to the subject's balance as well as the dependent variable in question. Subjects performed three blocks (7 H-reflexes/block) of standing control trials with the balance board supported, and seven blocks of balancing trials. Prior to each block, maximal M-waves were recorded to ensure electrode stability across blocks. Results indicated that the subjects were able to significantly reduce (p < .001) the gain the soleus H-reflex while balancing and after the balance training. As a group, the subjects decreased their peak to peak amplitude of the soleus H-reflex by 26.2 percent from the initial standing block to the last balancing block. Moreover, subjects were also able to significantly reduce the gain of their standing control H-reflexes, supporting the notion of longer-term adaptability of the spinal stretch reflex. It is concluded that the progressive reduction in the H-reflex gain with short-term training may represent functional adaptation in the central nervous system.

Adolescent↗
PubMed2005

Repeated visually-guided saccades improves postural control in patients with vestibular disorders.

One of the most recent and promising theoretical hypotheses for compensation of persistent asymmetry of dynamic vestibulo-ocular gain is sensory substitution. As a switch between oculomotor and vestibulo-ocular systems, saccadic eye movements are engaged in humans to compensate the angular displacement of the head towards the labyrinthine defective side thus preserving the foveal fixation of the target. This study focused on the possibility that saccadic eye movements might also compensate for the impaired vestibulo-spinal reflexes and force the postural system to a more effective control on upright stance and verified whether this sway-stabilizing effect could be applied to patients with vestibular disorders and balance dysfunction. In the first experiment, 27 patients with unilateral labyrinthine hypofunction, 24 patients with central vestibular disorders and 24 healthy volunteers were evaluated by static posturography in 3 different visual conditions: (a) eye open with fixation of a steady target, (b) eye closed, and (c) while performing horizontal visually-guided saccades. The percentage of individuals with a decreased body sway area during the oculomotor task was found to be higher in labyrinthine-defective patients as compared to those with central vestibular disorders and controls. In the second experiment, 46 patients with vestibular disorders both of central and peripheral origin, whose postural control improved by eye-tracking, as assessed by posturography, were later submitted to 12 consecutive training sessions based on repeated visually-guided saccades. Both the saccadic performances and postural control improved in all patients but a more pronounced effect was observed in those with peripheral vestibular disorders. Outcome of this rehabilitation technique was also corroborated by a general reduction of the perceived overall impairment from balance disorders as tested by a specific questionnaire.

Adult↗
PubMed1983

Vestibular-proprioceptive functions in 4 year olds: normative and regression analyses.

Normative data were obtained for 156 pre-school children's performances on measures of muscle tone, muscle co-contraction, standing balance, prone extension posture, flexion supine posture, asymmetrical tonic neck reflex, and postrotary nystagmus. Regression analysis indicated that these combined variables accounted for only 13.5 percent of the variance of postrotary nystagmus of 145 four year olds. However, if the data are examined only for children exhibiting nystagmus that is lower than 1 standard deviation below the mean, then these variables account for 50 percent of the variance of nystagmus. Prone extension posture, standing balance-eyes closed, and muscle tone account for 37 percent of the variance within this low-nystagmus population. These results are considered in light of the authors' previous studies demonstrating that, in learning-disabled children, vestibular-proprioceptive measures can be used clinically to predict which children will respond to sensory integration therapy with changes in postrotary nystagmus. These changes, according to sensory integration theory, reflect positive responses to therapy.

Child, Preschool↗
PubMed1999

Visual-vestibular interaction during transparent optokinetic stimulation in the rabbit.

Transparent motion is a visual stimulus condition that generates multiple motion vectors on the retina that can differ in speed, direction, and/or luminance. Transparent motion creates a conflict for retinal stabilization. In this study we investigated the effect of transparent visual motion on the oculomotor reflexes that provide retinal stabilization in the rabbit. In the first experimental condition, the animals were stationary. We presented one stationary and one oscillating visual pattern to the animals while varying the luminance of the patterns. We found that the optokinetic eye movement responses were fully determined by the luminance of the individual visual inputs, weighted for the total luminance. No effect of absolute stimulus intensity was found. In the second experimental condition we oscillated the animals, while using an identical visual stimulation paradigm. The contribution of the vestibulo-ocular reflex enhanced the response to the visual pattern, which was in agreement with the vestibular stimulus. This effect of vestibular stimulation was independent of the absolute intensity of the visual stimuli. From this result we conclude that the weighting process of the transparent visual patterns occurs upstream from the site of the visual-vestibular interaction. Both the visual weighting and the visual-vestibular interaction were dependent on stimulus frequency. In line with the properties of the visual and vestibular stabilization reflexes in isolation, the contribution of the vestibular system increased, whereas the influence of the optokinetic system decreased with increasing stimulus frequency.

Animals↗
PubMed1983

[Postnatal development of static vestibulo-ocular reactions in the rabbit--electromyographic studies].

The changes in the electric activity of the extraocular muscles as a consequence of static tilt stimulation were investigated in rabbits of different postnatal ages by the registration of the electromyogram. The postnatal development of the tonic vestibulo-ocular reflex in the rabbit runs parallel with the transition from an irregular fluctuating eye muscle activity during the first postnatal days to a constantly tonic muscle activity depending on the tilt position.

Animals↗
PubMed2002

Cerebellar nodulectomy impairs spatial memory of vestibular and optokinetic stimulation in rabbits.

Natural vestibular and optokinetic stimulation were used to investigate the possible role of the cerebellar nodulus in the regulation and modification of reflexive eye movements in rabbits. The nodulus and folium 9d of the uvula were destroyed by surgical aspiration. Before and after nodulectomy the vertical and horizontal vestibuloocular reflexes (VVOR, HVOR) were measured during sinusoidal vestibular stimulation about the longitudinal (roll) and vertical (yaw) axes. Although the gain of the HVOR (G(HVOR) = peak eye movement velocity/peak head velocity) was not affected by the nodulectomy, the gain of the VVOR (G(VVOR)) was reduced. The gains of the vertical and horizontal optokinetic reflexes (G(VOKR), G(HOKR)) were measured during monocular, sinusoidal optokinetic stimulation (OKS) about the longitudinal and vertical axes. Following nodulectomy, there was no reduction in G(VOKR) or G(HOKR). Long-term binocular OKS was used to generate optokinetic afternystagmus, OKAN II, that lasts for hours. After OKAN II was induced, rabbits were subjected to static pitch and roll, to determine how the plane and velocity of OKAN II is influenced by a changing vestibular environment. During static pitch, OKAN II slow phase remained aligned with earth-horizontal. This was true for normal and nodulectomized rabbits. During static roll, OKAN II remained aligned with earth-horizontal in normal rabbits. During static roll in nodulectomized rabbits, OKAN II slow phase developed a centripetal vertical drift. We examined the suppression and recovery of G(VVOR) following exposure to conflicting vertical OKS for 10-30 min. This vestibular-optokinetic conflict reduced G(VVOR) in both normal and nodulectomized rabbits. The time course of recovery of G(VVOR) after conflicting OKS was the same before and after nodulectomy. In normal rabbits, the head pitch angle, at which peak OKAN II velocity occurred, corresponded to the head pitch angle maintained during long-term OKS. If the head was maintained in a "pitched-up" or "pitched-down" orientation during long-term OKS, the subsequently measured OKAN II peak velocity occurred at the same orientation. This was not true for nodulectomized rabbits, who had OKAN II peak velocities at head pitch angles independent of those maintained during long-term OKS. We conclude that the nodulus participates in the regulation of compensatory reflexive movements. The nodulus also influences "remembered" head position in space derived from previous optokinetic and vestibular stimulation.

Animals↗
PubMedDate not supplied

Augmentation of cardiopulmonary baroreflex control of forearm vascular resistance in borderline hypertension.

Arterial baroreflex control of heart rate is impaired in young men with borderline or mild hypertension. Despite this impairment, these subjects often have exaggerated increases in vascular resistance during orthostatic stress. We considered the possibility that this exaggerated reflex vasoconstriction might reflect augmented cardiopulmonary baroreflex control of vascular resistance in borderline hypertension (BHT). Accordingly, we studied cardiopulmonary baroreflex control of forearm vascular resistance in nine BHT men with blood pressure intermittently above 150/90 mm Hg and in seven normotensive (NT) men. Cardiopulmonary baroreceptor input was reduced with lower body negative pressure (LBNP-5 to-20 mm HG), which decreases cardiac filling pressures. Baseline mean arterial pressure was 99 /+- 3 mm Hg (mean /+- SE) in BHT vs 83 /+- 2 mm Hg in NT (p less than 0.05). Baseline forearm resistance was also higher in BHT than in NT: 19 /+- 2 vs 13 /+-1 mm Hg/ml/min/100 ml or units (p less than 0.05). Reflex increases in forearm resistance during LBNP were greater (p less than 0.05) in BHT than in NT 8.6 /+- 1.7 vs 4.5 /+- 1.1 units during LBNP-20). Increases in arterial pressure and forearm resistance during a cold pressor test were not significantly different in the two groups. Thus, the augmented response to LBNP could not be attributed to a nonspecific influence of increased baseline resistance or a generalized abnormality in reflex control. In summary, the results of this study suggest that there is augmentation of the tonic inhibitory influence of cardiopulmonary baroreceptors in humans with BHT.

Adult↗
PubMed1999

Cervical root compression monitoring by flexor carpi radialis H-reflex in healthy subjects.

STUDY DESIGN: One-group, pretest-postest experimental research with repeated measures. OBJECTIVE: To determine the effect of head postural modification on the flexor carpi radialis H-reflex in healthy subjects. SUMMARY OF BACKGROUND DATA: H-reflex testing has been reported to be useful in evaluating and treating patients with lumbosacral and cervical radiculopathy. The idea behind this technique is that postural modification can cause further H-reflex inhibition, indicating more compression of the impinged nerve root, or recovery, indicating decompression of the root. Such assumptions cannot be supported unless the influence of normal head postural modification on the H-reflex in healthy subjects is studied. METHODS: Twenty-two healthy subjects participated in this study (14 men, 8 women; mean age, 39 +/- 9 years). The median nerve of the subjects at the cubital fossa was electrically stimulated (0.5 msec; 0.2 pulses per second [pps] at H-max), whereas the flexor carpi radialis muscle H-reflex was recorded by electromyography. The H-reflexes were recorded after the subject randomly maintained the end range of head-forward flexion, backward extension, rotation to the right and the left, lateral bending to the right and the left, retraction and protraction. These were compared with the H-reflex recorded during comfortable neutral positions. Data were recorded after the subject maintained the position for 30 seconds, to avoid the effect of dynamic postural modification on the H-reflex. Four traces were recorded in each position. During recording, the H-reflex was monitored by the M-response to avoid any changes in the stimulation-recording condition. RESULTS: Repeated multivariate analysis of variance was used to evaluate the significance of the difference among the H-reflex, amplitude, and latency, in various head positions. The H-reflex amplitude showed statistically significant changes (P < 0.001) with head postural modification. All head positions, except flexion, facilitated the H-reflex. Extension, lateral bending, and rotation toward the side of the recording produced higher reflex facilitation than the other positions. These results indicate that H-reflex changes may be caused by spinal root compression-decompression mechanisms. It may also indicate that relative spinal root decompression occurs in most head-neck postures except forward flexion. CONCLUSIONS: Head postural modification significantly influences the H-reflex amplitude but not the latency. This indicates that the H-reflex is a more sensitive predictor of normal physiologic changes than are latencies. The H-reflex modulation in various head positions may be-caused by relative spinal root compression-decompression mechanisms.

Adult↗
PubMed1996

Gait disturbance in Alzheimer's disease: a clinical study.

Gait disturbance is common in patients with Alzheimer's disease (AD). The aim of this study was to analyse the clinical gait syndromes of patients with AD using Nutt's classification. Fifty-five patients who satisfied the NINCDS-ADRDA criteria for probable AD and 55 controls were recruited from a geriatric and a psychogeriatric unit. Patients with classical musculoskeletal or neurological syndromes causing gait disturbance were excluded. A standardized neurological examination was carried out in all subjects. Twenty-two (40%) patients and ten (18%) controls had a higher level gait disorder (p < 0.01). The pattern of gait disturbance in AD patients varied according to the stage of the disease. Cautious gait was the commonest gait disorder in AD patients with mild dementia, while frontal gait disorder was the commonest disturbance in patients with severe dementia. The prevalence of frontal release signs (gegenhalten or any primitive reflex) was highest among patients with frontal gait disorder.

Activities of Daily Living↗
PubMed1988

Cardiopulmonary reflex before and after regression of left ventricular hypertrophy in essential hypertension.

Studies that have examined the cardiopulmonary receptor control of circulation in hypertension have produced conflicting results. In 10 normotensive subjects and in age-matched essential hypertensive subjects without (n = 10) or with left ventricular hypertrophy (n = 12), as well as in seven subjects of the latter group restudied after 1 year of treatment that induced regression of cardiac hypertrophy, we examined the cardiopulmonary reflex by increasing central venous pressure and stimulating cardiopulmonary receptors through passive leg raising and by reducing central venous pressure and deactivating cardiopulmonary receptors through nonhypotensive lower body negative pressure. Reflex responses were measured as changes in forearm vascular resistance (mean blood pressure divided by plethysmographically measured blood flow), plasma norepinephrine concentration, and plasma renin activity. In hypertensive subjects without left ventricular hypertrophy, stimulation and deactivation of cardiopulmonary receptors caused changes in forearm vascular resistance, norepinephrine concentration, and plasma renin activity that were modestly reduced as compared with those in normotensive subjects. However, all these changes were markedly reduced in hypertensive subjects with left ventricular hypertrophy. Following regression of left ventricular hypertrophy, the changes in vascular resistance, plasma norepinephrine, and plasma renin activity induced by cardiopulmonary receptor manipulation all improved markedly. These results demonstrate that cardiopulmonary receptor regulation of peripheral vascular resistance and of neurohumoral variables is impaired in essential hypertension and that the impairment is much more pronounced when this condition is associated with cardiac structural alterations. Therapeutic regression of these alterations, however, leads to a marked improvement of this reflex, with consequent favorable effects on circulatory homeostasis.

Adult↗
PubMed1986

Early neuromotor reflexes in infancy.

While motor milestones--the neurodevelopmental functional end point of the transitioning of the immature and mature primitive reflexes into volitional activity--have been highlighted in predicting future motor function, the primitive reflexes represent the earliest neurodevelopmental markers available for study. By pediatricians becoming familiar with their quantitative and qualitative aspects coupled with the time of their appearance and suppression, they will have this neuromotor tool available for the early detection of a significant motor handicap. Primitive reflexes II have been highlighted since they are available at birth to be clinically evaluated and followed during sequential office visits during the first 6 months of life, the time during which infants are more closely followed at office visits. Delay or deviancy (nonsequential appearance) of motor milestones are preceded by an exaggeration or delayed suppression of the primitive reflexes. It is anticipated that the study and standardization of an intrauterine primitive reflex profile will eventually lead to the identification of a high-risk fetus. This endeavor will be fostered by the further development and refinement of non-invasive roentgenographic techniques.

Female↗