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S Hamdy

Publications and source records attributed to S Hamdy.

33 records · Page 2Linked to original sources
PubMed1998

Sensorimotor modulation of human cortical swallowing pathways.

1. Transcranial magnetic stimulation over motor areas of cerebral cortex in man can activate short latency bilateral cortical projections to the pharynx and oesophagus. In the present paper we investigate the interaction between pathways from each hemisphere and explore how activity in these pathways is modulated by afferent feedback from the face, pharynx and oesophagus. 2. Comparison of unilateral and bilateral stimulation (using interstimulus intervals (ISIs) of 1, 5 or 10 ms between shocks) showed spatial summation of responses from each hemisphere at an ISI of 1 ms, indicating that cortical efferents project onto a shared population of target neurones. Such summation was not evident at ISIs of 5 or 10 ms. There was little evidence for transcallosal inhibition of responses from each hemisphere, as described for limb muscles. 3. Single stimuli applied to the vagus nerve in the neck or the supraorbital nerve, which alone produce intermediate (onset 20-30 ms) and long (50-70 ms) latency reflex responses in the pharynx and oesophagus, were used to condition the cortical responses. Compared with rest, responses evoked by cortical stimulation were facilitated when they were timed to coincide with the late part of the reflex. The onset latency was reduced during both parts of the reflex response. No facilitation was observed with subthreshold reflex stimuli. 4. Single electrical stimuli applied to the pharynx or oesophagus had no effect on the response to cortical stimulation. However, trains of stimuli at frequencies varying from 0.2 to 10 Hz decreased the latency of the cortically evoked responses without consistently influencing their amplitudes. The effect was site specific: pharyngeal stimulation shortened both pharyngeal and oesophageal response latencies, whereas oesophageal stimulation shortened only the oesophageal response latencies. 5. Cortical swallowing motor pathways from each hemisphere interact and their excitability is modulated in a site-specific manner by sensory input. The latter may produce a mixture of excitation and inhibition at both brainstem and cortical levels.

Adult↗
PubMed1998

Recovery of swallowing after dysphagic stroke relates to functional reorganization in the intact motor cortex.

BACKGROUND & AIMS: The aim of this study was to determine the mechanism for recovery of swallowing after dysphagic stroke. METHODS: Twenty-eight patients who had a unilateral hemispheric stroke were studied 1 week and 1 and 3 months after the stroke by videofluoroscopy. Pharyngeal and thenar electromyographic responses to magnetic stimulation of multiple sites over both hemispheres were recorded, and motor representations were correlated with swallowing recovery. RESULTS: Dysphagia was initially present in 71% of patients and in 46% and 41% of the patients at 1 and 3 months, respectively. Cortical representation of the pharynx was smaller in the affected hemisphere (5 +/- 1 sites) than the unaffected hemisphere (13 +/- 1 sites; P </= 0.001). Nondysphagic and persistently dysphagic patients showed little change in pharyngeal representation in either hemisphere at 1 and 3 months compared with presentation, but dysphagic patients who recovered had an increased pharyngeal representation in the unaffected hemisphere at 1 and 3 months (15 +/- 2 and 17 +/- 3 vs. 9 +/- 2 sites; P </= 0.02) without change in the affected hemisphere. In contrast, thenar representation increased in the affected hemisphere but not the unaffected hemisphere at 1 and 3 months (P </= 0.01). CONCLUSIONS: Return of swallowing after dysphagic stroke is associated with increased pharyngeal representation in the unaffected hemisphere, suggesting a role for intact hemisphere reorganization in recovery.

Aged↗
PubMed1998

Gut feelings about recovery after stroke: the organization and reorganization of human swallowing motor cortex.

Swallowing problems can affect as many as one in three patients in the period immediately after a stroke. In some cases this can lead to serious morbidity, in particular malnutrition and pulmonary aspiration. Despite this, swallowing usually recovers completely in the vast majority of patients within weeks. This impressive propensity for recovery is likely to relate to how the area of the motor cortex concerned with swallowing is organized and then reorganized after cerebral injury. Recent studies have indicated that swallowing has a bilateral but asymmetric inter-hemisphere representation within motor and premotor cortex. Damage to the hemisphere that has the greater swallowing output appears to predispose that individual to swallowing problems. However, because there is additional substrate for swallowing in the undamaged hemisphere, the capacity for compensatory reorganization in the contralateral motor cortex might be increased, leading to a greater likelihood of recovery. Swallowing might be an excellent system for studying cortical plasticity, and might prove useful in the development of new therapies aimed at accelerating reorganization in the undamaged hemisphere after unilateral cerebral injury.

Adaptation, Physiological↗
PubMed1998

Long-term reorganization of human motor cortex driven by short-term sensory stimulation.

Removal of sensory input can induce changes in cortical motor representation that reverse when sensation is restored. Here we ask whether manipulation of sensory input can induce long-term reorganization in human motor cortex that outlasts the initial conditioning. We report that for at least 30 minutes after pharyngeal stimulation, motor cortex excitability and area of representation for the pharynx increased, while esophagus representation decreased, without parallel changes in the excitability of brainstem-mediated reflexes. Therefore increased sensory input can drive long-term cross-system changes in motor areas of the cerebral cortex, which suggests that sensory stimulation might rehabilitate dysphagia, a frequent consequence of cerebral injury.

Adult↗
PubMed1998

Spinal and pudendal nerve modulation of human corticoanal motor pathways.

We investigated the effects of lumbosacral and pudendal nerve stimulation on the corticofugal pathways to the human external anal sphincter. In 11 healthy subjects, anal sphincter electromyographic responses, evoked to transcranial magnetic stimulation of the motor cortex, were recorded 5-500 ms after lumbosacral root or pudendal nerve stimulation. Lumbosacral and pudendal nerve stimulation alone evoked responses with amplitudes of 293 +/- 73 and 401 +/- 153 microV and latencies of 3.2 +/- 0.2 and 2.2 +/- 0.2 ms, respectively. Cortical stimulation also evoked responses with amplitudes of 351 +/- 104 microV and latencies of 20.9 +/- 1.1 ms. When lumbosacral or pudendal nerve stimulation preceded cortical stimulation, the cortically evoked responses were facilitated (P < 0.01), with the effect appearing greatest at 5-20 ms after both lumbosacral and pudendal excitation and at 50-100 ms after lumbosacral excitation alone. Our results demonstrate that cortical pathways to the external anal sphincter are facilitated by prior lumbosacral and pudendal nerve stimulation, indicating that sensorimotor interactions are important in the central neural control of sphincter function.

Adult↗
PubMed1998

Experiences with functional magnetic resonance imaging at 1 tesla.

Functional magnetic resonance imaging (fMRI) has been performed on a standard 1 T system using a pulse sequence developed to utilize blood oxygen level dependent (BOLD) contrast and an off-line analysis routine using correlation techniques. The sequence and the data analysis routine have been validated by reproducing the conventional hand movement paradigm studies reported by numerous other workers. Our work has then been extended to investigate cerebral foci for a tonic pain stimulus and the cortical representation of oesophageal stimulation. Both these studies relate to paradigms where the expected BOLD signal is significantly less than that encountered for motor or visual cortex paradigms. The results show good agreement with other modalities (positron emission tomography, magnetoencephalography and cortical evoked potentials). Performing fMRI at 1 T is slightly controversial. However, our successful study of demanding paradigms, using a standard clinical 1 T imaging system, has important implications for many other users operating at this field strength.

Brain↗
PubMed1997

Explaining oropharyngeal dysphagia after unilateral hemispheric stroke.

BACKGROUND: Oropharyngeal dysphagia occurs in up to a third of patients presenting with a unilateral hemiplegic stroke, yet its neurophysiological basis remains unknown. To explore the relation between cortical motor function of swallowing and oropharyngeal dysphagia, mylohyoid, pharyngeal, and thenar electromyographic responses to stimulation of affected and unaffected hemispheres were recorded in dysphagic and non-dysphagic patients. METHODS: The 20 patients studied had unilateral hemispheric stroke confirmed by computed tomography. Eight of them had associated swallowing difficulties. Electromyographic responses were recorded after suprathreshold transcranial magneto-electric stimulation of affected and unaffected hemispheres with a figure-of-eight coil. FINDINGS: Stimulation of the unaffected hemisphere evoked smaller pharyngeal responses in dysphagic patients than in non-dysphagic patients (mean 64 microV, median 48, interquartile range 44-86 vs 118 microV, 81, 73-150) (p < 0.02). With stimulation of the affected hemisphere, the pharyngeal responses were smaller than for the unaffected hemisphere but similar between the two patient groups (26 microV, 0, 0-48 vs 54 microV, 0, 0-80). Dysphagic and non-dysphagic patients showed similar mylohyoid and thenar responses to stimulation of the unaffected hemisphere as well as to stimulation of the affected hemisphere-unaffected mylohyoid (269 microV, 239, 89-372 vs 239 microV, 163, 133-307), thenar (572 microV, 463, 175-638 vs 638 microV, 485, 381-764); affected mylohyoid (60 microV, 41, 0-129 vs 96 microV, 0, 0-195); thenar (259 microV, 258, 0-538 vs 451 microV, 206, 8-717). INTERPRETATION: The findings indicate that dysphagia after unilateral hemispheric stroke is related to the magnitude of pharyngeal motor representation in the unaffected hemisphere.

Adult↗
PubMed1997

Identification of human brain loci processing esophageal sensation using positron emission tomography.

BACKGROUND & AIMS: Brain loci that process human esophageal sensation remain unidentified. The aim of this study was to identify the brain loci that process nonpainful and painful human esophageal sensation. METHODS: In 8 healthy subjects (7 men; age range, 24-47 years), distal esophageal stimulation was performed by repeatedly inflating a balloon at volumes that produced either no sensation, definite sensation, or pain. Two positron emission tomography scans were performed for each sensation using H2(15)O. Magnetic resonance brain scans were also performed in each subject, and the positron emission tomography data were coregistered with magnetic resonance scans. Analysis of covariance-corrected t images showing the contrasts definite sensation-baseline, pain-baseline, and pain-definite sensation were created. RESULTS: Nonpainful stimulation elicited bilateral activations along the central sulcus, insular cortex, and frontal/parietal operculum (P < 0.01). Painful stimulation produced more intense activations of the same areas and additional activation of the right anterior insular cortex and the anterior cingulate gyrus. Multiple areas of decreased activation were also observed; prominent among these was the right prefrontal cortex, which was inhibited during both nonpainful and painful stimulation. CONCLUSIONS: Esophageal sensation activates bilaterally the insula, primary somatosensory cortex, and operculum. The right anterior insular cortex and anterior cingulate gyrus process esophageal pain.

Adult↗
PubMed1997

Topographic mapping of trans-cranial magnetic stimulation data on surface rendered MR images of the brain.

We present a method for the coregistration and topographic mapping of trans-cranial magnetic stimulation (TCMS) data on surface rendered images of the cortex, derived from Magnetic Resonance Images (MRI). We describe the TCMS procedure and the methods used to locate the TCM stimulation sites in the MRI coordinate system, and the algorithms needed to depict the TCMS distribution as a pseudocolour contour map on the cortical surface. The methods are validated using TCMS data from the hand (thenar) and leg (tibialis muscle). The methods used correctly depict the expected motor representations of each of these areas and we therefore propose that this technique may be used as a functional imaging tool in the investigation of cortical function in both normals and patients.

Brain Mapping↗
PubMed1997

Cranial nerve modulation of human cortical swallowing motor pathways.

Animal data indicate that cortical swallowing pathways can be modulated by cranial nerve afferent stimulation. We therefore studied the effects of human trigeminal and vagal nerve excitation on the corticofugal pathways to the oropharynx and esophagus, using electromagnetic stimulation. Unilateral stimulation of either the trigeminal or vagus nerve evoked two distinct reflex electromyographic responses in the pharynx and esophagus, an early response (latency range 19-30 ms) and a late response (latency range 42-72 ms). In the mylohyoid muscles, however, only a single response was seen (latency range 36-64 ms). Cortical stimulation also evoked electromyographic responses in the mylohyoid muscles, pharynx, and esophagus, with latencies of 8.5 +/- 0.3, 9.3 +/- 0.3, and 10.1 +/- 0.4 ms, respectively. When either trigeminal or vagus nerve stimulation preceded cortical stimulation, the cortically evoked responses were facilitated, with maximal effects at interstimulation intervals of 30-200 ms for pharynx and esophagus (P < 0.02) and at interstimulation intervals of 50-100 ms for mylohyoid muscles (P < 0.05). Our results demonstrate that stimulation of human cranial nerve afferent fibers facilitates cortical swallowing motor pathways.

Adult↗
PubMed1996

The topographic representation of esophageal motor function on the human cerebral cortex.

BACKGROUND & AIMS: Corticofugal pathways to the human esophagus have been recently identified in humans using transcranial magnetic stimulation. The aim of this study was to determine the topographic representation of the esophagus on the cerebral cortex. METHODS: Focal magnetic stimulation of 1-cm areas was performed over both hemispheres in 10 healthy subjects. Esophageal electromyographic responses were recorded 2 cm below the upper esophageal sphincter. The studies were repeated to determine reproducibility in 3 subjects; in 2 subjects, esophageal topography was compared with thenar muscle topography. RESULTS: In all subjects, esophageal electromyographic responses were evoked by stimulation of either the right or left hemisphere. Largest amplitude responses were obtained anterior to those of the thenar muscles, indicating that the esophagus may be represented on either the anterior aspect of the motor cortex or on the premotor cortex. In all subjects, the area of response was asymmetric, being more extensive on the right hemisphere than on the left hemisphere in 8 subjects. In 2 subjects, the area of response on the left hemisphere was more extensive than on the right. Repeat studies showed that this asymmetry was consistent. CONCLUSIONS: Esophageal motor function shows bilateral cortical representation with consistent interhemispheric asymmetry.

Adult↗
PubMed1996

The cortical topography of human swallowing musculature in health and disease.

Because no detailed information exists regarding the topographic representation of swallowing musculature on the human cerebral cortex in health or disease, we used transcranial magnetic stimulation to study the cortical topography of human oral, pharyngeal and esophageal musculature in 20 healthy individuals and the topography of pharyngeal musculature in two stroke patients, one with and one without dysphagia. Our results demonstrate that swallowing musculature is discretely and somatotopically represented on the motor and premotor cortex of both hemispheres but displays interhemispheric asymmetry, independent of handedness. Following stroke, dysphagia appeared to be associated with smaller pharyngeal representation on the intact hemisphere, which increases in size with recovery of swallowing.

Adolescent↗
PubMed1995

Early experience with extracorporeal shockwave Dornier lithotriptor "compact".

One of the latest developments in extracorporeal shockwave lithotripsy (SWL) is a combination of an electromagnetic energy source with an upgraded parallel online ultrasound imaging for localization. The device is compact, requiring no significant installation or site preparation. Furthermore, it increases the margin of safety of SWL by virtue of the continuous ultrasound monitoring. A hundred sessions of SWL were performed on 88 patients using the Dornier Compact machine. Ninety three renal units having an average of 1.7 stones were treated (two had upper ureteric stones). Of the 135 stones, 2 (1.5%) were radiolucent and 4 (3%) were of faint opacity. Intravenous sedation was used in all patients except one 13-year-old patient, who required general anesthesia. Patients received an average of 2409 shocks per session, and the maximum power setting ranged from 1 to 6 (average 4.7). A plain film was obtained immediately before and after treatment. Early adverse effects were uncommon, and all were mild. Patients were followed by plain films at 2 weeks and 3 months. In 35 sessions (25 solitary and 10 multiple stones), the stones were considered completely fragmented; in 63 sessions, the stones (43 solitary and 20 multiple) were judged to be partial fragmented; and 2 sessions (solitary stones) resulted in poor fragmentation. The mean (+/- SD) stone dimension in the group with complete fragmentation was 9 +/- 4.8 (range 2-24) mm, compared with 11 +/- 6.3 (range 2-38) mm in those with no or partial fragmentation (P = 0.0095). After 2 weeks, 23 of 69 systems (33%) were stone free, while 46 showed residual stones.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1991

Hormonal changes in headache patients.

Seventy-three patients with headache underwent serum and cerebrospinal fluid (CSF) radioimmunoassays of follicle-stimulating hormone (FSH), luteinizing hormone (LH), cortisol and prolactin. Serum FSH showed significant increases in all headache patients while serum LH increased only in females. Such a rise of serum FSH and LH is attributed to disturbances of the sleep-wake cycle. On the other hand, serum cortisol was significantly decreased in the male headache patients, probably due to altered circadian rhythm. Serum prolactin remained within normal limits. CSF prolactin, FSH and LH showed detectable levels in all headache sufferers compared to undetectable levels in control subjects, while CSF cortisol was significantly reduced.

Chronic Disease↗