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Biomedical subjects

A Bronstein

Publications and source records attributed to A Bronstein.

At least 19 recordsLinked to original sources
PubMed2004

EFNS task force--therapy of nystagmus and oscillopsia.

An overview of possible treatment options for oculomotor disorders that prevent clear vision is given. Downbeat nystagmus, upbeat nystagmus, seesaw nystagmus, periodic alternating nystagmus, acquired pendular nystagmus, and saccadic oscillations such as opsoclonus/ocular flutter are discussed. In addition, superior oblique myokymia and vestibular paroxysmia are reviewed. All treatment recommendations available in the literature are classified as class C only. In general, only some of the patients benefit from the treatment.

Advisory Committees↗
PubMed2001

Interference between postural control and mental task performance in patients with vestibular disorder and healthy controls.

OBJECTIVES: To determine whether interference between postural control and mental task performance in patients with balance system impairment and healthy subjects is due to general capacity limitations, motor control interference, competition for spatial processing resources, or a combination of these. METHOD: Postural stability was assessed in 48 patients with vestibular disorder and 24 healthy controls while they were standing with eyes closed on (a) a stable and (b) a moving platform. Mental task performance was measured by accuracy and reaction time on mental tasks, comprising high and low load, spatial and non-spatial tasks. Interference between balancing and performing mental tasks was assessed by comparing baseline (single task) levels of sway and mental task performance with levels while concurrently balancing and carrying out mental tasks. RESULTS: As the balancing task increased in difficulty, reaction times on both low load mental tasks grew progressively longer and accuracy on both high load tasks declined in patients and controls. Postural sway was essentially unaffected by mental activity in patients and controls. CONCLUSIONS: It is unlikely that dual task interference between balancing and mental activity is due to competition for spatial processing resources, as levels of interference were similar in patients with vestibular disorder and healthy controls, and were also similar for spatial and non-spatial tasks. Moreover, the finding that accuracy declined on the high load tasks when balancing cannot be attributed to motor control interference, as no motor control processing is involved in maintaining accuracy of responses. Therefore, interference between mental activity and postural control can be attributed principally to general capacity limitations, and is hence proportional to the attentional demands of both tasks.

Adult↗
PubMed1999

Human endothelial cell life extension by telomerase expression.

Normal human endothelial cells, like other somatic cells in culture, divide a limited number of times before entering a nondividing state called replicative senescence. Expression of the catalytic component of human telomerase, human telomerase reverse transcriptase (hTERT), extends the life span of human fibroblasts and retinal pigment epithelial cells beyond senescence without causing neoplastic transformation (Bodnar, A. G., Ouellette, M., Frolkis, M., Holt, S. E., Chiu, C. P., Morin, G. B., Harley, C. B., Shay, J. W., Lichtsteiner, S., and Wright, W. E. (1998) Science 279, 349-352; Jiang, X., Jimenez, G., Chang, E., Frolkis, M., Kusler, B., Sage, M., Beeche, M., Bodnar, A., Wahl, G., Tlsty, T., and Chiu, C.-P. (1999) Nat. Genet. 21, 111-114). Here, we show that both human large vessel and microvascular endothelial cells also bypass replicative senescence after introduction of hTERT. For the first time, we report that hTERT expression in these life-extended vascular cells does not affect their differentiated and functional phenotype and that these cells maintain their angiogenic potential in vitro. Furthermore, hTERT(+) microvascular endothelial cells have normal karyotype, and hTERT(+) endothelial cell strains do not exhibit a transformed phenotype. Relative to parental cells at senescence, hTERT-expressing endothelial cells exhibit resistance to induction of apoptosis by a variety of different conditions. Such characteristics are highly desirable for designing vascular transplantation and gene therapy delivery systems in vivo.

Apoptosis↗
PubMed1998

Postural responses to vibration of neck muscles in patients with uni- and bilateral vestibular loss.

Postural responses to vibration applied unilaterally to the dorsal neck muscles were recorded with a sway platform in 11 patients with bilateral vestibular loss (BLD), 13 patients with unilateral vestibular lesions (ULD) and 19 normal subjects. In the normals, the vibration induced a forward postural deviation. Vibration failed to induce postural sway in the BLD patients but induced a backwards head movement in 7 patients. In the ULD patients, vibration contralateral to the lesion induced normal forward sway, whereas ipsilateral vibration resulted in sway directed to the side of the lesion and backwards. The findings demonstrate the importance of concurrent vestibular signals in determining the behavioural response to neck afferent input. We propose that in normal subjects the intact vestibular signal gives no confirmation that a head movement has occurred so it is assumed that the lower body has tilted forwards which provokes a compensatory sway. In the total absence of vestibular function the neck signal may represent a real head movement so the preferential response is a head tilt to restore upright posture. The vestibular imbalance in the ULD patients is roughly equivalent to the asymmetrical signals obtained in a normal subject during head rotation to the intact side. The stretch signal induced by ipsi-lesional vibration confirms possible head rotation, thus provoking a compensatory postural sway. Copyright 1998 Elsevier Science B.V. All rights reserved

Journal Article↗
PubMed1998

Horizontal otolith-ocular responses in humans after unilateral vestibular deafferentation.

We studied horizontal eye movements evoked by lateral whole body translation in nine patients who underwent vestibular nerve section. Preoperatively, all had preserved caloric function on both sides. Testing was performed before, 1 week and 6-10 weeks after surgery. Patients were seated upright in an electrically powered car running on a linear track. The car executed acceleration steps of 0.24 g, randomly to the left and right in the dark. The normal response consisted of a bidirectionally symmetrical nystagmus with compensatory slow phases. Response asymmetry of the slow-phase velocity of the desaccaded and averaged eye position signal was less than 13% in normals (n = 21). Before surgery, patients' responses were mostly symmetrical. Postoperatively, responses were diminished or absent with head acceleration towards the operated ear in all patients, causing a marked asymmetry which averaged 56% after correction for spontaneous nystagmus. On follow-up, responses regained symmetry. Thus, early after vestibular nerve section, a single utricle produces a normal LVOR only with ipsilateral head translation. Therefore, afferents for the LVOR seem to originate from the mid-lateral area of the macula, where hair cells are stimulated in their on-direction during ipsilateral head translation. Compensation may depend on recovery of the off-directional responses from lateral hair cells of the remaining utricle.

Acceleration↗
PubMed1998

Encoding target-trunk relative position: cervical versus vestibular contribution.

The contribution of cervical and vestibular cues in signaling the changes in target-trunk relative positions during self-motion was investigated. Normal subjects (Ss) were shown a LED flashed in the peripheral visual field in a dark room. Ss were then passively rotated about the vertical axis in one of three different conditions: (1) head chair-fixed (vestibular condition); (2) head earth-fixed (relaxed neck condition); and (3) head earth-fixed, but with the Ss actively attempting to turn it (activated neck condition). The Ss were then required to indicate, with their unseen index finger, the position of the previously flashed target. It was found that pointing at the memorized target was similarly accurate in the relaxed neck condition and in the activated neck condition. In the vestibular condition, pointing accuracy dropped significantly. These results suggest that neck proprioceptive signals are more effective than vestibular ones in signaling relative changes in the position of stationary objects with respect to the body during head-trunk motion. The finding that cervically mediated estimates were unchanged during active contraction of the neck muscles may suggests that efference copy signals may help interpret the change in the afferent signals caused by voluntary neck muscle activation.

Adult↗
PubMed1998

Changes in heart rate and respiration rate in patients with vestibular dysfunction following head movements which provoke dizziness.

Patients with vestibular dysfunction often complain of additional symptoms typical of panic disorder and/or hyperventilation. This study investigated whether autonomic and respiratory symptoms reported by patients with vestibular disorders were associated with objective changes in heart and respiration rate following head movements provoking dizziness. Subjective ratings of symptoms and anxiety and objective measures of heart and respiration rate were obtained from 29 patients and 16 healthy controls immediately before and after the subjects performed three standardised sets of vigorous head movements. Within-group analyses revealed greater increases in respiration rate following head movement among patients who complained of more somatic symptoms, both during the previous 2 months and following head movement.

Adult↗
PubMed1997

Dissociation between the perception of body verticality and the visual vertical in acute peripheral vestibular disorder in humans.

Estimates of the subjective visual and postural vertical were obtained from five patients with acute peripheral vestibular lesions and 20 normal subjects. The visual vertical was assessed by asking the subjects to align a target line to earth vertical by means of remote control. Postural vertical judgments were obtained by exposing them to rotational displacements in the roll plane while sitting on a motor-driven chair and requiring them to align their body to vertical using a joystick control. While the patients showed strong deviations of the visual vertical towards the lesion side, their postural vertical judgments remained veridical. We conclude that the above perceptions are not processed identically and that the participating sensory systems are differently weighted during these tasks.

Adult↗
PubMed1997

The functional effectiveness of neck muscle reflexes for head-righting in response to sudden fall.

Reflex head-righting in normal and labyrinthine-defective (LD) subjects was compared to identify the relative functional effectiveness of vestibular-collic and cervico-collic myotactic reflexes. To restrict stimuli largely to the head and neck, subjects lay supine, supported up to the shoulders on a horizontal bed with their head supported in a sling over the edge. The head fell freely as the sling was released with an electromagnetic catch. Head drops were delivered with the subjects instructed to relax and accept the fall passively or to actively right the head as fast as possible. With both instructions, righting responses in normal subjects commenced with electromyographic (EMG) bursts in the sternocleidomastoid (SCM) at 24.5 ms latency, which was reflected in a deceleration of the downwards head velocity. The latency of the earliest EMG responses in LD subjects was 67.4 ms, accompanied by similar deceleration. It is assumed that the earliest response in normal subjects is vestibular, whereas in LDs the SCM stretch reflex is the earliest response. These reflexes are followed at circa 100 ms by more intense EMG activity due to voluntary movement, but braking of head fall is evident before voluntary activity takes effect. Righting was more effective in normal subjects than in LDs, and when "active" normal subjects made more vigorous righting responses than when "passive"; whereas active righting in LDs was no better than passive. The results demonstrate that reflex responses contribute significantly to head-righting. The vestibular contribution gives an advantage over stretch reflexes alone and also assists in voluntary enhancement of reflex responses.

Acceleration↗
PubMed1997

Postural responses to vibration of neck muscles in patients with idiopathic torticollis.

Vibration of the dorsal muscles of the neck, simulating lengthening, in standing man causes a visible forwards tilt of the body shown on posturography as a tonic sagittal sway deviation. According to the theory that posture is organized with respect to a 'body schema' this deviation is a result of an interpretation of the concurrent neck afferent and vestibular signals. Considering the hypothesis that neck afferent signals may be misinterpreted in patients with spasmodic torticollis (ST) causing abnormal postural responses, we recorded body sway induced by unilateral dorsal neck muscle vibration in 22 idiopathic ST patients (19 treated with botulinum toxin) during upright stance with eyes closed. Comparison groups were 19 normal subjects and 11 patients with bilateral loss of vestibular function (labyrinthine defective, LD) in whom neck afference should be intact. Both treated and untreated ST and LD patients had absent or diminished sway deviations. When sway deviation did occur, it was sagitally oriented as with normal subjects and unrelated to ST head turns. In most ST and LD patients, neck vibration induced neck extension, an effect which is observed in normal subjects only if the torso is retrained. The results suggest that neck proprioceptive input retains local postural functions in ST, however, it is relatively ignored in the context of the whole body postural control and spatial orientation. The mild disorders of vestibular function reported in torticollis patients may be due to an inability to calibrate vestibular signals by reference to corroborative signals from neck proprioception.

Achilles Tendon↗
PubMed1996

Postural responses to vibration of neck muscles in patients with unilateral vestibular lesions.

Postural responses to vibration applied unilaterally to dorsal neck muscles were recorded with a sway platform in nine patients with unilateral vestibular lesions and 19 normal subjects. In normals, the vibration induced a forward postural deviation. In patients, vibration of the neck contralateral to the lesion induced normal forward sway, whereas ipsilateral vibration resulted in sway of lower amplitude than normal and predominantly in the direction of the lesion or backwards. It is suggested that the proprioceptive error signal introduced by the neck vibration combined with an asymmetrical vestibular input due to a unilateral vestibular lesion provoked an erroneous representation of head position in patients resulting in a redirection of their body sway.

Humans↗
PubMed1996

Interreader reliability for a new classification of lumbar disk disease.

RATIONALE AND OBJECTIVES: The nomenclature that divides disk herniations into protrusions and extrusions may increase the specificity of magnetic resonance (MR) imaging for clinically important lesions. Our goal was to determine this terminology's interreader reliability. METHODS: Three readers who were unaware of patients' histories independently read MR images of 34 consecutive patients with back pain. Readers classified disks at the lowest three lumbar levels as normal, bulging, protruded, or extruded. Kappa and weighted kappa values were the primary measures of agreement. RESULTS: Weighted kappa values showed fair-to-moderate agreement. Kappas for the dichotomous decision of extrusion present or absent were more variable, ranging from 0 to .78. Major disagreements (greater than a single category) occurred with 6.2% of all comparisons and in 10 of 34 volunteers; five involved extrusions. CONCLUSION: Overall, readers achieved moderate agreement for this new nomenclature. However, agreement for the presence or absence of an extrusion was less reliable.

Adult↗
PubMed1995

Neck muscle responses to abrupt free fall of the head: comparison of normal with labyrinthine-defective human subjects.

1. EMG responses from sternocleidomastoid (SCM) and orbicularis oculi were recorded in subjects who lay supine with their heads cradled in a sling. When the sling released abruptly, their heads fell freely. Normal and bilateral labyrinthine-defective subjects (LDs) were studied. 2. The normal response in SCM was a small burst of excitation at 22-25 ms latency, of 18 ms duration. This merged into a larger, later burst. The drop also produced eye blinks at 22-38 ms. 3. The onset of the SCM response in LDs was delayed (56-73 ms) even though the latency of their eye blinks was normal. 4. We conclude that the early response at approximately 22 ms in normal subjects is mediated by a vestibulocollic reflex. The delayed activity in LDs may be a stretch reflex. This is the first demonstration of the latency of the vestibulocollic pathway to natural stimulation in man.

Acceleration↗
PubMed1994

Click-evoked vestibular activation in the Tullio phenomenon.

Click-evoked vestibulocollic reflexes were studied in a patient with a unilateral Tullio phenomenon (sound induced vestibular symptoms) and the findings were compared with those of a group of normal subjects. Compared with normal subjects, the reflexes elicited from her symptomatic side were large and had an abnormally low threshold, but retained a normal waveform. The click-evoked responses in this patient show changes consistent with her symptomatology and are indicative of a pathological increase in the normal vestibular sensitivity to sound.

Adult↗
PubMed1990

[Evaluation of systolic and diastolic left ventricular function in acute myocardial infarction by aortic echogram].

A noninvasive method for the measurement of the cardiac output and diastolic ventricular function was evaluated by aortic echogram in a group of patients with acute myocardial infarction (AMI). The following parameters were employed: average of initial and late aortic cusp separation (ACS), left ventricular ejection time (EP) and amplitude of aortic posterior wall during ejection (AA). The following formula was used: cardiac output (CO) = (ACS x EP) x 100 + AA x HR. Diastolic ventricular function was evaluated by the left auricle emptying index (LAEI) described by Strunk et al. This last relationship X/OA where X is the movement of the aortic posterior wall (AP) at the first third of passive diastole, and OA is the total aortic movement during the passive diastole. All patients were followed by cardiac output measurements by thermodilution and pulmonary capillary pressure (PCP). Twenty measurements were made in fourteen subjects; for CO a good lineal correlation was found (r = 0.81). As for diastolic ventricular function, LAEI reached a value of 0.49 (+/- 0.23); normal value was 0.82 (p less than 0.01); it was significantly diminished showing the stiffness of the chamber. The utilization of aortic echogram and the analysis of movement of APW result in a non invasive reliable procedure that can be repeated to evaluate the hemodynamic situation in AMI.

Aged↗