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At least 1,081 records · Page 60Linked to original sources
PubMed2006

Influence of vision and static stretch of the calf muscles on postural sway during quiet standing.

The purpose of this experimental study was to evaluate the effects of vision and stretching of the calf muscles on postural sway during quiet standing. Under pre-stretch conditions, participants stood on a force plate for 30s and the sway of the ground reaction force center of pressure was recorded. The following postural sway variables were calculated off-line: sweep speed, sway speed, standard deviation, maximal mediolateral range, maximal anteroposterior range, mean mediolateral position and mean anteroposterior position. For post-stretch conditions, participants stood quietly on a device that was utilized to impose a static 3 min ankle joint dorsiflexion stretch. Immediately thereafter, participants moved onto the force platform where postural sway parameters were again recorded. Randomized eyes-open and eyes-closed conditions were tested in both cases. Results showed that postural sway significantly increased due to stretch (sweep speed, sway speed, standard deviation, maximal anteroposterior range, mean anteroposterior position), as well as eye closure (sweep speed, sway speed, standard deviation, maximal mediolateral range, maximal anteroposterior range). The interaction between stretch and eye closure was also significant (sweep speed, sway speed, standard deviation, maximal mediolateral range), suggesting that there were only minor increases in postural sway after stretch under the eyes-open condition. It was suggested that stretching of the calf muscles has the effect of increasing postural sway, although this effect can be greatly compensated for when vision is included.

Adult↗
PubMed2006

Deficient limb support is a major contributor to age differences in falling.

Older adults are more likely than young to fall upon a loss of balance, yet the factors responsible for this difference are not well understood. This study investigated whether age-related differences in movement stability, limb support, and protective stepping contribute to the greater likelihood of falling among older adults. Sixty young and 41 older, safety-harnessed, healthy adults were exposed to a novel and unexpected forward slip during a sit-to-stand task. More older than young adults fell (76% vs. 30%). Falls in both age groups were related to lesser stability and lower hip height at first step touchdown, with 97.1% of slip outcomes correctly classified based on these variables. Decreases in hip height at touchdown had over 20 times greater effect on the odds of falling than equivalent decreases in stability. Three age differences placed older adults at greater risk of falling: older adults had lower and more slowly rising hips at slip onset, they were less likely to respond to slipping with ample limb support, and they placed their stepping foot less posterior to their center of mass. The first two differences, each associated with deficient limb support, reduced hip ascent and increased hip descent. The third difference resulted in lesser stability at step touchdown. These results suggest that deficient limb support in normal movement patterns and in the reactive response to a perturbation is a major contributor to the high incidence of falls in older adults. Improving proactive and reactive limb support should be a focus of fall prevention efforts.

Accidental Falls↗
PubMed2005

Effects of immersion in virtual reality on postural control.

In the present study, we examined the effects of the time lag between visual scene and the head movement in the virtual reality (VR) world on motion sickness and postural control in healthy volunteers. After immersion in VR with additional time lags (from 0 to 0.8 s) to the inherent delay (about 250 ms), the visual-vestibular conflict induced a slight motion sickness in experimental subjects, but no change was noticed in the body sway path with eyes open and closed. However, Romberg ratio of body sway path with eyes closed divided by that with eyes open after immersion in VR was significantly decreased in comparison with that before immersion in VR. Since Romberg ratio is an index of visual dependency on postural control, this finding indicates that the immersion in VR decreases the visual dependency on postural control. It is suggested that adaptation to visual-vestibular conflict in VR immersion increases the contribution of vestibular and somatosensory inputs to postural control by ignoring the conflicting delayed visual input in the VR world. VR may be a promising treatment for visual vertigo in vestibular patients with unsuccessful compensation by its ability to induce vestibular and somatosensory reweighing for postural control.

Adult↗
PubMed2004

Brain activation patterns during imagined stance and locomotion in functional magnetic resonance imaging.

Posture and gait are sensorimotor actions that involve peripheral, spinal, and supraspinal structures. To investigate brain activity during stance and locomotion, 13 healthy subjects were asked to stand, walk, run, and lie down; subsequently, they were trained to imagine standing, walking, running, and lying [imagined lying as rest condition in functional magnetic resonance imaging (fMRI)]. Separate and distinct activation/deactivation patterns were found for the three imagined conditions: (1) standing imagery was associated with activation in the thalamus, basal ganglia, and cerebellar vermis; (2) walking imagery was associated with activation in the parahippocampal and fusiform gyri (areas involved in visuospatial navigation), occipital visual areas, and in the cerebellum; (3) running imagery caused a predominantly cerebellar activation in the vermis and adjacent hemispheres (six times larger than during imagination of walking or standing), but activations in the parahippocampal and fusiform gyri were smaller than during walking. Deactivations were found for walking and running, but not for standing imagery. They were located in the vestibular (posterior insula, superior temporal gyrus, supramarginal gyrus) and somatosensory (postcentral gyrus) cortex with right-hemispheric dominance. These findings support the concept of a hierarchical organization of posture and locomotion. Automated locomotion, for example, running, is based on spinal generators whose pace is driven by the cerebellar locomotor region. Deactivation in the vestibular and somatosensory cortex prevents adverse interactions with the optimized spinal pattern and sensory signals; this confirms earlier findings of a multisensory inhibition during unhindered locomotion. During slow walking, spatial navigation, mediated by the parahippocampal cortex, becomes more important. Postural control during standing involves a low intensity cerebellar activity and sensorimotor control via the thalamus and basal ganglia.

Adult↗
PubMed2005

The role of vestibular rehabilitation in the treatment of Meniere's disease.

OBJECTIVE: To study the role of vestibular rehabilitation is treating patients with Meniere's disease. METHODS: We examined all Meniere's patients presenting to our tertiary care specialized vestibular clinic during a 1-year period. All patients underwent a standardized history and physical examination, a complete auditory-vestibular test battery, and a set of physical therapy tools to measure balance function. RESULTS: A subset of patients suffered from disequilibrium or unsteadiness between attacks. Once the acute fluctuating symptoms of Meniere's were controlled in this group of individuals, all of them underwent vestibular physical therapy and demonstrated significant improvement in balance function on both objective and self-report tests. CONCLUSIONS: Due to the fluctuating nature of the disorder, vestibular physical therapy has had a limited role in the treatment of Meniere's disease. In general, rehabilitation has been used only as a postoperative treatment for the acute vertigo seen after vestibular neurectomy or labyrinthectomy. This is the first report advocating the role of vestibular physical therapy in a group of patients receiving medical therapy of intraear medicines (other that gentamicin).

Adult↗
PubMed2005

Intrinsic membrane properties of vertebrate vestibular neurons: function, development and plasticity.

Central vestibular neurons play an important role in the processing of body motion-related multisensory signals and their transformation into motor commands for gaze and posture control. Over recent years, medial vestibular nucleus (MVN) neurons and to a lesser extent other vestibular neurons have been extensively studied in vivo and in vitro, in a range of species. These studies have begun to reveal how their intrinsic electrophysiological properties may relate to their response patterns, discharge dynamics and computational capabilities. In vitro studies indicate that MVN neurons are of two major subtypes (A and B), which differ in their spike shape and after-hyperpolarizations. This reflects differences in particular K(+) conductances present in the two subtypes, which also affect their response dynamics with type A cells having relatively low-frequency dynamics (resembling "tonic" MVN cells in vivo) and type B cells having relatively high-frequency dynamics (resembling "kinetic" cells in vivo). The presence of more than one functional subtype of vestibular neuron seems to be a ubiquitous feature since vestibular neurons in the chick and frog also subdivide into populations with different, analogous electrophysiological properties. The ratio of type A to type B neurons appears to be plastic, and may be determined by the signal processing requirements of the vestibular system, which are species-variant. The membrane properties and discharge pattern of type A and type B MVN neurons develop largely post-natally, through the expression of the underlying ion channel conductances. The membrane properties of MVN neurons show rapid and long-lasting plastic changes after deafferentation (unilateral labyrinthectomy), which may serve to maintain their level of activity and excitability after the loss of afferent inputs.

Action Potentials↗
PubMed2007

Ultrasound evaluation of dynamic responses of female pelvic floor muscles.

Ultrasound imaging of the pelvic floor carries diagnostically important information about the dynamic response of the pelvic floor muscles (PFM) to potentially incontinence-producing stress, which cannot be readily captured and assimilated by the observer during the scanning process. We presented an approach based on motion tracking quantitatively to analyze the dynamic parameters of PFM on the ano-rectal angle (ARA). Perineal ultrasonography was performed on 22 asymptomatic females and nine stress urinary incontinent (SUI) patients with a broad age distribution and parity. The ventral-dorsal and cephalad-caudad movements of the ARA were resolved and kinematic parameters, in terms of displacement, trajectory, velocity and acceleration, were analyzed. The results revealed the possible mechanisms of PFM responses to prevent the urine from incontinence in fast and stress events such as coughs. The statistical analyses showed that the PFM responses of the healthy subjects and the SUI patients are significantly different in both the supine and standing experiments.

Adult↗
PubMed1999

Cardiac positron emission tomography imaging with [11C]hydroxyephedrine, a specific tracer for sympathetic nerve endings, and its functional correlates in congestive heart failure.

The integrative mechanisms of autonomic dysfunction in congestive heart failure (CHF) remain poorly understood. We sought to study cardiac retention of [11C]hydroxyephedrine (HED), a specific tracer for sympathetic presynaptic innervation, and its functional correlates in CHF. Thirty patients with mild to moderate heart failure underwent resting cardiac HED positron emission tomography imaging, spectrum analysis testing of systolic pressure and heart rate variability in the resting supine and 70 degrees head-up tilt positions, and testing of baroreflex sensitivity. Compared with control subjects, global myocardial HED retention index was reduced by 30% (p <0.01) in patients with CHF. The HED retention index did not correlate significantly with heart rate variability. However, it correlated with baroreflex sensitivity at rest (r = 0.43, p = 0.05) and with systolic pressure low-frequency (0.03 to 0.15 Hz) variability at head-up tilt (r = 0.76, p <0.01), as well as with low-frequency systolic pressure variability response from baseline to tilt (r = 0.75, p <0.01). We conclude that cardiac HED retention is reduced in patients with CHF. This correlates with blunted vascular sympathetic effector responses during posture-induced reflex activation and baroreflex control of heart rate, suggesting an interdependence between cardiac presynaptic innervation abnormalities and neural mechanisms important to blood pressure maintenance in CHF.

Blood Pressure↗
PubMed2001

Role of the medial medullary reticular formation in relaying vestibular signals to the diaphragm and abdominal muscles.

Changes in posture can affect the resting length of respiratory muscles, requiring alterations in the activity of these muscles if ventilation is to be unaffected. Recent studies have shown that the vestibular system contributes to altering respiratory muscle activity during movement and changes in posture. Furthermore, anatomical studies have demonstrated that many bulbospinal neurons in the medial medullary reticular formation (MRF) provide inputs to phrenic and abdominal motoneurons; because this region of the reticular formation receives substantial vestibular and other movement-related input, it seems likely that medial medullary reticulospinal neurons could adjust the activity of respiratory motoneurons during postural alterations. The objective of the present study was to determine whether functional lesions of the MRF affect inspiratory and expiratory muscle responses to activation of the vestibular system. Lidocaine or muscimol injections into the MRF produced a large increase in diaphragm and abdominal muscle responses to vestibular stimulation. These vestibulo-respiratory responses were eliminated following subsequent chemical blockade of descending pathways in the lateral medulla. However, inactivation of pathways coursing through the lateral medulla eliminated excitatory, but not inhibitory, components of vestibulo-respiratory responses. The simplest explanation for these data is that MRF neurons that receive input from the vestibular nuclei make inhibitory connections with diaphragm and abdominal motoneurons, whereas a pathway that courses laterally in the caudal medulla provides excitatory vestibular inputs to these motoneurons.

Abdominal Muscles↗
PubMed2003

The effects of pitch tilt on postrotatory nystagmus in cats.

When the head is tilted away from the upright position immediately after termination of earth-vertical axis (EVA) head rotation at a constant velocity, the rotation axis of postrotatory nystagmus (PRN) is gradually directed toward gravity (spatial reorientation). During roll tilt, the extent of the axis shift varies among species. In cats, the reorientation is limited to about 30-45 degrees of head tilt. In the present study, we examined features of PRN during pitch tilt in cats. The animals were rotated about EVA at a constant velocity of 100 degrees /s for 120 s. Within 2 s after stopping EVA rotation, the animals were tilted toward the pitch plane by as much as +/-90 degrees (nose-down or nose-up) in steps of 15 degrees. Eye movements were measured with 3D magnetic search coils. The angle of the PRN plane and its slow phase eye velocity (SPV) were measured. The duration of PRN decreased as pitch tilt increased regardless of whether the direction was nose-up or nose-down. The mean time constant of SPV was significantly longer for nose-up than for nose-down. PRN maintained its horizontal orientation without any vertical drift during pitch tilt, but there was little reorientation toward gravity. That is, no significant torsional component of SPV emerged to reorient the eyes according to gravity. Our results indicate that spatial reorientation depends on head orientation. For the PRN responses after pitch tilts in cats, the interactions of semicircular canal and otolith inputs in the central vestibular system might be vestigial.

Animals↗
PubMed1995

The clinician's role in teaching proper infant feeding techniques.

The species-specific advantages and significant nutritional and health benefits of breast-feeding are widely acknowledged. Less recognized are the advantages of the process of breast-feeding itself. Adherence to the natural mechanics of breast-feeding will preclude many of the problems associated with improper bottle feeding. For example, the semiupright position of the infant during breast-feeding helps eliminate the entry of milk into the middle ear and reduces choking and regurgitation. The action of suckling during breast-feeding minimizes the intake of air. In addition, the direct eye contact that is natural to breast-feeding fosters bonding, and the close body contact promotes a sense of security in the child. These advantages, so natural to breast-feeding, are likely to be absent from bottle feeding unless some of the natural techniques associated with breast-feeding are adopted. This article describes various aspects of the breast-feeding process with the goal of urging practitioners to instruct patients to transfer these techniques to bottle feeding. In so doing, clinicians may help their patients avoid the hazards of improper bottle feeding.

Bottle Feeding↗
PubMed1976

Postural detrusor hyperreflexia.

Postural changes in bladder function have been documented previously only in female incontinent patients without evidence of neurologic or urologic disease. In our study the syndrome of postural hyperreflexia is described in patients of both sexes having a variety of neurological disorders. The investigations showed impaired function of supraspinal control of the sacral micturition center.

Adolescent↗
PubMed2001

Hydromorphone-3-glucuronide: a more potent neuro-excitant than its structural analogue, morphine-3-glucuronide.

In humans, hydromorphone (HMOR) is metabolised principally by conjugation with glucuronic acid to form hydromorphone-3-glucuronide (H3G), a close structural analogue of morphine-3-glucuronide (M3G), the major metabolite of morphine. In a previous study we described the biochemical synthesis of H3G together with a preliminary evaluation of its pharmacology which revealed that it is a neuroexcitant in rats in a manner analogous to M3G. Thus the aims of the current study were to quantify the neuro-excitatory behaviours evoked by intracerebroventricular (icv) H3G in the rat and to define its potency relative to M3G. Groups of adult male Sprague-Dawley rats received icv injections (1 microL) of H3G (1 - 3 microg), M3G (2 - 7 microg) or vehicle via a stainless steel guide cannula that had been implanted stereotaxically seven days prior to drug administration. Behavioural excitation was monitored by scoring fifteen different behaviours (myoclonic jerks, chewing, wet-dog-shakes, rearing, tonic-clonic-convulsions, explosive motor behaviour, grooming, exploring, general activity, eating, staring, ataxia, righting reflex, body posture, touch evoked agitation) immediately prior to icv injection and at the following post-dosing times: 5, 15, 25, 35, 50, 65 and 80 min. H3G produced dose-dependent behavioural excitation in a manner analogous to that reported previously for M3G by our laboratory and reproduced herein. H3G was found to be approximately 2.5-fold more potent than M3G, such that the mean (+/- S.D.) ED50 values were 2.3 (+/- 0.1) microg and 6.1 (+/- 0.6) microg respectively. Thus, our data clearly imply that if H3G crosses the BBB with equivalent efficiency to M3G, then the myoclonus, allodynia and seizures observed in some patients dosed chronically with large systemic doses of HMOR, are almost certainly due to the accumulation of sufficient H3G in the central nervous system, to evoke behavioural excitation.

Animals↗