Biomedical subjects

S Hamdy

Publications and source records attributed to S Hamdy.

At least 19 recordsLinked to original sources

PubMed2006

Deglutitive laryngeal closure in stroke patients.

BACKGROUND: Dysphagia has been reported in up to 70% of patients with stroke, predisposing them to aspiration and pneumonia. Despite this, the mechanism for aspiration remains unclear. AIMS: To determine the relationship between bolus flow and laryngeal closure during swallowing in patients with stroke and to examine the sensorimotor mechanisms leading to aspiration. METHODS: Measures of swallowing and bolus flow were taken from digital videofluoroscopic images in 90 patients with stroke and 50 healthy adults, after repeated volitional swallows of controlled volumes of thin liquid. Aspiration was assessed using a validated Penetration-Aspiration Scale. Oral sensation was also measured by electrical stimulation at the faucial pillars. RESULTS: After stroke, laryngeal ascent was delayed (mean (standard deviation (SD)) 0.31 (0.06) s, p<0.001), resulting in prolongation of pharyngeal transit time (1.17 (0.07) s, p<0.001) without a concomitant increase in laryngeal closure duration (0.84 (0.04) s, p = 0.9). The delay in laryngeal elevation correlated with both the severity of aspiration (r = 0.5, p<0.001) and oral sensation (r = 0.5, p<0.001). CONCLUSIONS: After stroke, duration of laryngeal delay and degree of sensory deficit are associated with the severity of aspiration. These findings indicate a role for sensorimotor interactions in control of swallowing and have implications for the assessment and management of dysphagia after stroke.

Adult↗

PubMed2006

Neurophysiological evaluation of healthy human anorectal sensation.

Patients with functional gastrointestinal disorders often demonstrate abnormal visceral sensation. Currently, rectal sensation is assessed by manual balloon distension or barostat. However, neither test is adaptable for use in the neurophysiological characterization of visceral afferent pathways by sensory evoked potentials. The aim of this study was to assess the reproducibility and quality of sensation evoked by electrical stimulation (ES) and rapid balloon distension (RBD) in the anorectum and to apply the optimum stimulus to examine the visceral afferent pathway with rectal evoked potentials. Healthy subjects (n = 8, median age 33 yr) were studied on three separate occasions. Variability, tolerance, and stimulus characteristics were assessed with each technique. Overall ES consistently invoked pain and was chosen for measuring rectal evoked potential whereas RBD in all cases induced the strong urge to defecate. Rectal intraclass correlation coefficient (ICC) for ES and RBD (0.82 and 0.72, respectively) demonstrated good reproducibility at pain/maximum tolerated volume but not at sensory threshold. Only sphincter ICC for ES at pain showed acceptable between-study reproducibility (ICC 0.79). Within studies ICC was good (>0.6) for anorectal ES and RBD at both levels of sensation. All subjects reported significantly more unpleasantness during RBD than ES (P < 0.01). This study demonstrates that ES and RBD are similarly reproducible. However, the sensations experienced with each technique differed markedly, probably reflecting differences in peripheral and/or central processing of the sensory input. This is of relevance in interpreting findings of neuroimaging studies of anorectal sensation and may provide insight into the physiological characteristics of visceral afferent pathways in health and disease.

Adolescent↗

PubMed2006

Assessing the temporal reproducibility of human esophageal motor-evoked potentials to transcranial magnetic stimulation.

BACKGROUND: Although the electrophysiological properties and reproducibility of somatic limb motor evoked potentials (MEPs) to transcranial magnetic stimulation (TMS) are well characterized, little is known about the reproducibility of MEPs for viscerosomatic structures such as the esophagus. AIM: To determine the temporal reproducibility of esophageal MEPs to TMS. METHODS: MEPs to TMS were recorded from the proximal esophagus, using a swallowed catheter housing a pair of electrodes, in eight healthy subjects at five stimulus intensities (SI) (motor threshold [MT] to 20% above MT). For each SI, 20 consecutive TMS stimuli at 5-second intervals were delivered over a single scalp site (dominant hemisphere at site exhibiting MT at lowest SI) and repeated 40 and 80 minutes thereafter. MEP amplitudes and latencies were measured, and means were sequentially calculated for each SI and then log-transformed. The repeatability coefficients (RC) for the three time points were calculated across each set of 20 stimuli and presented as an exponential ratio. RESULTS: Best RC (amplitude/latency) were achieved at 120% SI relative to MT, being 1.8/1.2 (optimal = 1.0). For lower intensities of 115%, 110%, 105%, and 100% SI, the RC were 2.1/1.2, 2.1/1.1, 2.4/1.2, and 2.6/1.4, respectively. For all SI, the greatest reductions in RC occurred over the first 10 stimuli, with little additional gain beyond this number. CONCLUSIONS: Latencies of esophageal MEP to TMS across intensities are highly reproducible, whereas amplitudes are more stimulus intensity-dependent, being most reliable and reproducible at the highest stimulus strengths. SIGNIFICANCE: Using careful parameters, TMS can be used reliably in future studies of viscerosomatic structures, although the size of the response variability needs to be taken into account when assessing changes in cortico-fugal activity.

Adult↗

PubMed2006

Dysphagia in stroke patients.

Swallowing musculature is asymmetrically represented in both motor cortices. Stroke affecting the hemisphere with the dominant swallowing projection results in dysphagia and clinical recovery has been correlated with compensatory changes in the previously non-dominant, unaffected hemisphere. This asymmetric bilaterality may explain why up to half of stroke patients are dysphagic and why many will regain a safe swallow over a comparatively short period. Despite this propensity for recovery, dysphagia carries a sevenfold increased risk of aspiration pneumonia and is an independent predictor of mortality. The identification, clinical course, pathophysiology, and treatment of dysphagia after stroke are discussed in this review.

Central Nervous System Diseases↗

PubMed2005

Sacral nerve stimulation reduces corticoanal excitability in patients with faecal incontinence.

BACKGROUND: Sacral nerve stimulation (SNS) can produce symptomatic relief in patients with faecal incontinence. Moreover, peripheral nerve stimulation has been shown to affect brain function. The aim of this study was to determine whether SNS might produce important changes in cortical activity linked to improved continence. METHODS: In an experimental study, ten women with intractable faecal incontinence (mean age 51.3 years) were serially mapped with transcranial magnetic stimulation before and immediately after 14 days of temporary SNS (15 Hz, pulse width 210 micros), and then 2 weeks later. Anal sphincter electromyographic responses were recorded to cortical stimulation of multiple points over a scalp grid covering the bilateral medial cortex. Continence scores, anorectal manometry and rectal sensitivity data were also collected. RESULTS: SNS improved global symptom scores in the majority of patients; mean(s.e.m.) continence scores fell from 16.9(1.6) to 10.6(1.8) (P = 0.042). Cortical mapping showed a consistent decrease in corticoanal representation and overall excitability immediately after SNS compared with baseline (mean(s.e.m.) 38,083(13,669) versus 42,507(13,297) microV s; P = 0.017), which was reversed 2 weeks after SNS wire removal. CONCLUSION: SNS produces symptom benefit in patients with faecal incontinence that is associated with a reversible reduction in corticoanal excitability. SNS therefore drives dynamic brain changes that may play a functional role in influencing anal continence.

Adult↗

PubMed2005

The upper oesophageal sphincter.

The upper oesophageal sphincter (UOS) is a high-pressure zone comprising functional activity of three adjacent muscles together with cartilage and connective tissue. Its primary function is to allow food into the oesophagus and prevent air ingestion. However, it must also allow the reflux of material during belching or vomiting. Cricopharyngeus is the most important muscle with contributions from inferior pharyngeal constrictor and cervical oesophagus. Basal tone within the UOS is contributed to by all three muscles with asymmetry in the axial plane. Relaxation of the UOS occurs during swallowing as well as in sleep while UOS pressure rises with stress, slow oesophageal distension, intra-oesophageal acid infusion and pharyngeal stimulation with air or water. Many physiological characteristics have been attributed to UOS function following videofluoroscopic swallow examinations, manometry and electromyography but a range of normal values remains controversial and their utility uncertain. The result has been that pathological change is inconsistently characterized and management is instigated without a satisfactory evidence base. In this article, we review the anatomy, physiology and pathophysiology of the UOS along with the current opinions on investigation and treatment of UOS dysfunction.

Esophageal Sphincter, Upper↗

PubMed2004

Dissociating the spatio-temporal characteristics of cortical neuronal activity associated with human volitional swallowing in the healthy adult brain.

Human swallowing represents a complex highly coordinated sensorimotor function whose functional neuroanatomy remains incompletely understood. Specifically, previous studies have failed to delineate the temporo-spatial sequence of those cerebral loci active during the differing phases of swallowing. We therefore sought to define the temporal characteristics of cortical activity associated with human swallowing behaviour using a novel application of magnetoencephalography (MEG). In healthy volunteers (n = 8, aged 28-45), 151-channel whole cortex MEG was recorded during the conditions of oral water infusion, volitional wet swallowing (5 ml bolus), tongue thrust or rest. Each condition lasted for 5 s and was repeated 20 times. Synthetic aperture magnetometry (SAM) analysis was performed on each active epoch and compared to rest. Temporal sequencing of brain activations utilised time-frequency wavelet plots of regions selected using virtual electrodes. Following SAM analysis, water infusion preferentially activated the caudolateral sensorimotor cortex, whereas during volitional swallowing and tongue movement, the superior sensorimotor cortex was more strongly active. Time-frequency wavelet analysis indicated that sensory input from the tongue simultaneously activated caudolateral sensorimotor and primary gustatory cortex, which appeared to prime the superior sensory and motor cortical areas, involved in the volitional phase of swallowing. Our data support the existence of a temporal synchrony across the whole cortical swallowing network, with sensory input from the tongue being critical. Thus, the ability to non-invasively image this network, with intra-individual and high temporal resolution, provides new insights into the brain processing of human swallowing.

Adult↗

PubMed2003

Changes in pharyngeal corticobulbar excitability and swallowing behavior after oral stimulation.

Faucial pillar (FP) stimulation is commonly used in swallowing rehabilitation, yet its physiological basis remains uncertain. We investigated the effects of intraoral FP stimulation on human corticobulbar excitability and swallowing behavior, to explore the possibility of a central mechanism for functional change. In 10 healthy subjects, corticobulbar projections to pharynx were investigated with transcranial magnetic stimulation, via intraluminal electrodes, before and up to 1 h after 10 min of electrical FP stimulation with three frequencies (0.2, 1, and 5 Hz) or sham and peripheral (median nerve) stimulation. In a second study, swallowing behavior was assessed with videofluoroscopy before and after FP stimulation. FP stimulation at 5 Hz inhibited the corticobulbar projection (-14 +/- 6%, P < 0.02) and lengthened swallow response time (+114 +/- 24%, P = 0.02). By comparison, FP stimulation at 0.2 Hz facilitated this projection (+60 +/- 28%, P < 0.04), without enhancing swallowing behavior. Neither 1-Hz, sham, nor median nerve stimulation altered excitability. Thus changes in corticobulbar excitability to FP stimulation are frequency dependent with implications for the treatment for neurogenic swallowing dysfunction.

Adult↗

PubMed2003

Modulation of human swallowing behaviour by thermal and chemical stimulation in health and after brain injury.

Few data support thermal or chemical stimulation as therapy for neurogenic dysphagia. Our aims were to explore the behavioural effects of thermal (cold) and chemical (citrus) modalities on water swallowing in health (n = 65, mean age 45 years, 44 females) and acute stroke (n = 22, mean age 67 years, eight females). Multiple randomized timed 50-mL swallowing tests were performed for each of four water conditions: (a) room temperature (RT), (b) cold (CD), (c) citrus (CT) and (d) combined cold and citrus (CD + CT). The inter-swallow interval (ISI), swallowing volume velocity (speed), and volume per swallow (capacity) were measured. In health, compared to RT, only CD + CT slowed the speed (12.3 +/- 0.5 vs 10.3 +/- 0.5 mL s(-1), P < 0.03) and decreased the capacity (16.4 +/- 0.9 vs 14.6 +/- 0.7 mL per swallow, P < 0.02) of swallowing. ISI was unaffected, except by CD + CT in healthy young subjects (<60 years) where it was reduced (1.44 +/- 0.02 vs 1.30 +/- 0.02 s, P < 0.02). Despite smaller volumes ingested by stroke patients, CD + CT, compared to RT, again slowed both the speed (3.8 +/- 0.4 vs 4.5 +/- 0.5 mL s(-1), P < 0.03) and capacity (7.6 +/- 0.7 vs 8.5 +/- 0.7 mL per swallow, P < 0.03) of swallowing but had no effect on ISI. We conclude that combined thermal and chemical modification of water consistently alters swallowing behaviour in health and after cerebral injury. These findings have relevance in the management of neurogenic swallowing problems.

Adult↗

PubMed2001

Magnetoencephalographic response characteristics associated with tongue movement.

Whole-head magnetoencephalography (MEG) was employed to study the sources of activation evoked by both active tongue movement and swallowing in five healthy subjects. Evoked magnetic fields were adequately explained in both paradigms by a time-varying single-dipole model which localized in the tongue in all subjects. No additional brain sources were detectable. Therefore, MEG detects fields associated with tongue movement that best fit a single-dipole source in the tongue. Future electrophysiological brain activation studies where tongue movement is likely should be aware of this observation since the tongue behaves like a strong current dipole.

Adult↗

PubMed2001

Induction of cortical swallowing activity by transcranial magnetic stimulation in the anaesthetized cat.

Transcranial magnetic stimulation (TMS) over human fronto-central areas of scalp can activate short latency responses in the muscles of the face, pharynx and oesophagus. However, the physiological relationship between this early activity and the swallowing activity programmed by the brainstem central pattern generator (CPG) remains unclear. The aim of this study was to explore the relationship between TMS-induced early muscle and late swallowing activities in the feline model. Twelve adult cats were studied under light anaesthesia. Mylohyoid and oesophageal EMG, together with pharyngeal, upper oesophageal sphincter (UOS) and upper oesophageal manometry, were recorded to single-pulse TMS of cat cortex. TMS at low stimulation intensities evoked consistent short latency EMG responses in the mylohyoid and oesophageal muscles (6.1 +/- 1.2 ms and 12.7 +/- 0.7 ms, respectively), and early contractile activity in the UOS (latency 31.8 +/- 3.6 ms). By contrast, TMS at high intensities induced swallowing activity as indicated by mylohyoid EMG, and UOS relaxation (latencies 1.1 +/- 0.4 s and 0.8 +/- 0.1 s, respectively). Both the early muscle and late swallowing activities were intensity-dependent, increasing stimulus strength producing a reduction in latency and greater number of swallows. The characteristics of the early response suggest an oligosynaptic projection from cortex to swallowing muscles. The induction of swallows at high intensities suggests a requisite for greater recruitment of cortical motoneurones, or associated swallowing regions.

Animals↗

PubMed2001

Physiology and pathophysiology of the swallowing area of human motor cortex.

Swallowing problems can affect as many as one in three patients in the period immediately after stroke. Despite this, in the majority of cases, recovery usually occurs to a safe level after a month or two. In this review, we show how the organization of the cortical projections to swallowing muscles can account for many of the clinical observations on swallowing after stroke and explain why recovery is common in the long term. In addition, we examine approaches that may be useful in speeding up recovery of swallowing. Swallowing may be a useful model in which to study central nervous reorganization after injury.

Deglutition↗

PubMed2000

Cortical processing of human somatic and visceral sensation.

Somatic sensation can be localized precisely, whereas localization of visceral sensation is vague, possibly reflecting differences in the pattern of somatic and visceral input to the cerebral cortex. We used functional magnetic resonance imaging to study the cortical processing of sensation arising from the proximal (somatic) and distal (visceral) esophagus in six healthy male subjects. Esophageal stimulation was performed by phasic distension of a 2 cm balloon at 0.5 Hz. For each esophageal region, five separate 30 sec periods of nonpainful distension were alternated with five periods of similar duration without distension. Gradient echoplanar images depicting bold contrast were acquired using a 1.5 T GE scanner. Distension of the proximal esophagus was localized precisely to the upper chest and was represented in the trunk region of the left primary somatosensory cortex. In contrast, distension of the distal esophagus was perceived diffusely over the lower chest and was represented bilaterally at the junction of the primary and secondary somatosensory cortices. Different activation patterns were also observed in the anterior cingulate gyrus with the proximal esophagus being represented in the right midanterior cingulate cortex (BA 24) and the distal esophagus in the perigenual area (BA32). Differences in the activation of the dorsolateral prefrontal cortex and cerebellum were also observed for the two esophageal regions. These findings suggest that cortical specialization in the sensory-discriminative, affective, and cognitive areas of the cortex accounts for the perceptual differences observed between the two sensory modalities.

Adult↗

PubMed2000

Organization and reorganization of human swallowing motor cortex: implications for recovery after stroke.

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 to a safe level in the majority of patients within weeks. This propensity for recovery is likely to relate to how the swallowing motor cortex is organized and then reorganized after cerebral injury. In this review, we examine present knowledge on the cortical control of swallowing in humans, and examine the aspects of its organization that are important for compensating for recovery after damage. In addition, we examine approaches which may be useful in speeding up the process of recovery. Swallowing may turn out to be a useful model for studying central nervous system plasticity.

Animals↗

PubMed1999

The cortical topography of human anorectal musculature.

BACKGROUND & AIMS: The muscles of the anorectum are important in the volitional control of continence, yet virtually no information exists on their cortical representation in humans. METHODS: Topographic cortical mapping of both cerebral hemispheres was performed in 9 healthy subjects by applying suprathreshold transcranial magnetic stimulation to individual points on a scalp grid centered over the vertex and then recording the electromyographic responses from the external anal sphincter, rectum, and tibialis anterior muscles. RESULTS: Cortically evoked anal and rectal response latencies were similar (20.2 +/- 1.7 and 19.8 +/- 1.5 milliseconds, respectively) and were shorter than those from the anterior tibialis muscle (right, 29.7 +/- 2.3 milliseconds; left, 29.9 +/- 1.8 milliseconds; P < 0.0005). Cortical mapping showed that the anal responses were bilaterally represented on the superior motor cortex (Brodmann area 4) of both cerebral hemispheres; a similar topography was found for the rectal responses. By comparison, the tibialis responses showed predominantly contralateral medial motor cortex representation. Subtle but consistent differences in the degree of bilateral hemispheric representation were also apparent both between and within individuals for the anal responses and to a lesser extent for the rectal responses. CONCLUSIONS: The anorectal musculature has bilateral motor cortex representation with similar topography, but there is intersubject variation in the degree of symmetry.

Adult↗

PubMed1999

Laterality effects of human pudendal nerve stimulation on corticoanal pathways: evidence for functional asymmetry.

BACKGROUND: Although motor and sensory pathways to the human external anal sphincter are bilateral, a unilateral pudendal neuropathy may still disrupt anal continence. Anal continence can, however, be preserved despite unilateral pudendal damage, and so to explain those differing observations, we postulated that pudendal innervation might be asymmetric. AIMS: To explore the individual effects of right and left pudendal nerve stimulation on the corticofugal pathways to the human external anal sphincter and thus assess evidence for functional asymmetric pelvic innervation. METHODS: In eight healthy subjects, anal sphincter electromyographic responses, evoked to transcranial magnetic stimulation of the motor cortex, were recorded 5-500 msec after digital transrectal electrical conditioning stimuli applied to each pudendal nerve. RESULTS: Right or left pudendal nerve stimulation evoked anal responses of similar latencies but asymmetric amplitudes in six subjects: dominant responses (>50% contralateral side) from the right pudendal in four subjects and from the left in two. Cortical stimulation also evoked anal responses with amplitude 448 (121) microV and latency 20.9 (1.1) msec. When cortical stimulation was preceded by pudendal nerve stimulation, the cortical responses were facilitated at interstimulus intervals of 5-20 msec. Dominant pudendal nerve stimulation induced greater facilitation of the cortically evoked responses than the non-dominant nerve. CONCLUSIONS: Cortical pathways to the external anal sphincter are facilitated by pudendal nerve conditioning, in an asymmetric manner. This functional asymmetry may explain the presence and absence of anal incontinence after unilateral pudendal nerve injury.

Adult↗

PubMed1999

Cortical activation during human volitional swallowing: an event-related fMRI study.

Functional magnetic resonance imaging (fMRI) provides a safe, noninvasive method for studying task-related cortical neuronal activity. Because the cerebral cortex is strongly implicated in the control of human swallowing, we sought to identify its functional neuroanatomy using fMRI. In 10 healthy volunteers, a swallow event-related paradigm was performed by injecting 5 ml water bolus into the oral cavity every 30 s. Whole brain functional magnetic susceptibility -weighted spiral imaging data were simultaneously acquired over 600 s on a 1.5-T magnetic resonance scanner, utilizing the blood oxygenation level-dependent technique, and correlation maps were generated using both >99% percentile rank and spatial extent thresholding. We observed areas of increased signal change consistently in caudal sensorimotor cortex, anterior insula, premotor cortex, frontal operculum, anterior cingulate and prefrontal cortex, anterolateral and posterior parietal cortex, and precuneus and superiomedial temporal cortex. Less consistent activations were also seen in posterior cingulate cortex and putamen and caudate nuclei. Activations were bilateral, but almost every region, particularly the premotor, insular, and frontal opercular cortices, displayed lateralization to one or the other hemisphere. Swallow-related cortical activity is multidimensional, recruiting brain areas implicated in processing motor, sensory, and attention/affective aspects of the task.

Adult↗

PubMed1999

Identification of the cerebral loci processing human swallowing with H2(15)O PET activation.

Lesional and electrophysiological data implicate a role for the cerebral cortex in the initiation and modulation of human swallowing, and yet its functional neuroanatomy remains undefined. We therefore conducted a functional study of the cerebral loci processing human volitional swallowing with 15O-labeled water positron emission tomography (PET) activation imaging. Regional cerebral activation was investigated in 8 healthy right handed male volunteers with a randomized 12-scan paradigm of rest and water swallows (5 ml/bolus, continuous infusion) at increasing frequencies of 0.1, 0.2, and 0.3 Hz, which were visually cued and monitored with submental electromyogram (EMG). Group and individual linear covariate analyses were performed with SPM96. In five of eight subjects, the cortical motor representation of pharynx was subsequently mapped with transcranial magnetic stimulation (TMS) in a posthoc manner to substantiate findings of hemispheric differences in sensorimotor cortex activation seen with PET. During swallowing, group PET analysis identified increased regional cerebral blood flow (rCBF) (P < 0.001) within bilateral caudolateral sensorimotor cortex [Brodmann's area (BA) 3, 4, and 6], right anterior insula (BA 16), right orbitofrontal and temporopolar cortex (BA 11 and 38), left mesial premotor cortex (BA 6 and 24), left temporopolar cortex and amygdala (BA 38 and 34), left superiomedial cerebellum, and dorsal brain stem. Decreased rCBF (P < 0.001) was also observed within bilateral posterior parietal cortex (BA 7), right anterior occipital cortex (BA 19), left superior frontal cortex (BA 8), right prefrontal cortex (BA 9), and bilateral superiomedial temporal cortex (BA 41 and 42). Individual PET analysis revealed asymmetric representation within sensorimotor cortex in six of eight subjects, four lateralizing to right hemisphere and two to left hemisphere. TMS mapping in the five subjects identified condordant interhemisphere asymmetries in the motor representation for pharynx, consistent with the PET findings. We conclude that volitional swallowing recruits multiple cerebral regions, in particular sensorimotor cortex, insula, temporopolar cortex, cerebellum, and brain stem, the sensorimotor cortex displaying strong degrees of interhemispheric asymmetry, further substantiated with TMS. Such findings may help explain the variable nature of swallowing disorders after stroke and other focal lesions to the cerebral cortex.

Adult↗