Flow-mediated dilatation following wrist and upper arm occlusion in humans: the contribution of nitric oxide.
(41/534)
Flow-mediated dilatation (FMD) of the brachial artery assessed by high-resolution ultrasound is widely used to measure endothelial function. However, the technique is not standardized, with different groups using occlusion of either the wrist or the upper arm to induce increased blood flow. The validity of the test as a marker of endothelial function rests on the assumption that the dilatation observed is endothelium-dependent and mediated by nitric oxide (NO). We sought to compare the NO component of brachial artery dilatation observed following wrist or upper arm occlusion. Dilatation was assessed before and during intra-arterial infusion of the NO synthase inhibitor N(G)-monomethyl-L-arginine (L-NMMA) following occlusion of (i) the wrist (distal to ultrasound probe) and (ii) the upper arm (proximal to ultrasound probe) for 5 min in ten healthy males. Dilatation was significantly greater after upper arm occlusion (upper arm, 11.62+/-3.17%; wrist, 7.25+/-2.49%; P=0.003). During L-NMMA infusion, dilatation after wrist occlusion was abolished (from 7.25+/-2.49% to 0.16+/-2.24%; P<0.001), whereas dilatation after upper arm occlusion was only partially attenuated (from 11.62+/-3.17% to 7.51+/-2.34%; P=0.006). The peak flow stimulus was similar after wrist and upper arm occlusion. We conclude that dilatation following upper arm occlusion is greater than that observed after wrist occlusion, despite a similar peak flow stimulus. L-NMMA infusion revealed that FMD following wrist occlusion is mediated exclusively by NO, while dilatation following upper arm occlusion comprises a substantial component not mediated by NO, most probably related to tissue ischaemia around the brachial artery. FMD following wrist occlusion may be a more valid marker of endothelial function than dilatation following upper arm occlusion. (+info)
Distal radial fractures in young goalkeepers: a case for an appropriately sized soccer ball.
(42/534)
OBJECTIVES: To assess the rate of wrist fractures in young goalkeepers sustained by the specific mechanism of "saving the ball" and the potential influence of ball size and environmental conditions. METHODS: A prospective, clinic based study in one institution over a 17 month period. Patients were identified by specific questioning. Information on play circumstances and subsequent clinical progress was documented. RESULTS: Twenty nine fractures of the distal radius were identified in young goalkeepers (age range 6-15 years) as a direct result of saving the ball. Most were managed simply in a plaster cast. Three patients required minor surgical interventions, and all fractures went on to unite without significant complications. Where ball size was known, 12 of the 15 fractures in children aged 11 years or less occurred as the result of impact with an adult sized ball compared with three when a junior ball was involved. This is statistically significant (p = 0.039). In the 10 children aged 12-15 years, only one fracture involved a junior ball; this is also statistically significant (p = 0.027). Six of the injuries (21%) occurred when the ball was kicked by an adult. Injuries occurred in both organised and informal games throughout the year. CONCLUSIONS: This specific mechanism of injury has not been widely acknowledged nor has the potential influence of ball size as a causative factor been examined. Recommendations for an appropriately sized soccer ball for young players exist but are not in universal use. Increased awareness of this particular injury mechanism is required. (+info)
Delayed and prolonged effects of a near threshold EPSP on the firing time of human alpha-motoneurones.
(43/534)
In order to investigate the effects of near-threshold excitatory inputs on the precise timing of the action potentials during the tonic discharge of human motoneurones, the activity of single motor units was recorded in the extensor carpi radialis muscles while tendon taps (indentation, 0.1 mm; duration, 1 ms) were being delivered irregularly at a mean rate of 0.8 s(-1). New methods of analysis, such as the phase response function, were used to study the relative changes in the interspike interval (ISI1) during which the stimulus was being delivered and in the three subsequent intervals (ISI2, ISI3, ISI4) as a percentage of the pre-stimulus interspike interval (ISI0). The consistency of the effects of the actual stimulus as regards the spontaneous variability was assessed by comparing the data with those obtained with virtual stimulation. When the stimulus occurred at the end of ISI1, and triggered a spike, ISI1 and ISI3 were generally shortened, whereas ISI2 was lengthened, probably due to the negative correlation induced by the summation of the after-hyperpolarisations (AHPs). When the stimulus occurred in the middle of ISI1 without triggering a spike, ISI1, ISI2 and more rarely ISI3 were shortened. Lastly, when the stimulus occurred during the AHP scoop in ISI1, ISI2 was shortened although ISI1 remained unchanged. ISI4 was not consistently affected in any of these cases. The present results show that the tendon tap-induced inputs (probably from muscle spindle primary endings) mediated delayed and prolonged shortening effects of the ISIs on most of the alpha-motoneurones tested (n = 16). These effects undetected in classic peri-stimulus histogram analysis may involve long-lasting conductance changes although the contribution of polysynaptic pathways cannot be excluded. The changes in ISI were quite moderate (< 15% of ISI) but highly consistent. Their functional involvement in the synchronisation or desynchronisation processes and/or the mechanisms of optimisation of muscle contraction still remains to be explored. (+info)
Superficialization of the wrist native arteriovenous fistula for effective hemodialysis vascular access construction.
(44/534)
BACKGROUND: It is commonly known that the best type of vascular access for chronic hemodialysis, defined as the one with the lowest number of complications and longest use, is the primary (Brescia-Cimino) radiocephalic fistula. One reason for the impossibility of its creation is that the vein vessel on the forearm is located too deeply, which is primarily caused by the patients' obesity. METHODS: In 24 obese patients the superficialization procedure of the venous part of fistula under the skin was performed. RESULTS: In 23 patients of this group, an easy and uncomplicated fistula puncturing was achieved. One patient had the complication of fistula clotting. CONCLUSION: Subcutaneous transposition of the arterialized median antebrachial vein is a simple and effective method of an adequate distal native fistula creation in patients with deeply located forearm veins. (+info)
Common drive in motor units of a synergistic muscle pair.
(45/534)
The interaction among the motor units of the extensor carpi radialis longus (ECRL) and the extensor carpi ulnaris (ECU) muscles in man was studied during wrist extensions in which the two muscles acted as synergists. Intramuscular recordings were obtained using special quadrifilar needle electrodes. Isometric wrist extensions at 20-30% of the maximal effort were studied. The electromyographic (EMG) signals were decomposed into the individual motor-unit action potential trains comprising the signal. The interaction among motor units were characterized by the estimated time-varying mean firing rate and the cross-correlation between the time-varying mean firing rates of pairs of motor units. Pairs of motor units within each muscle as well as pairs of motor units across the muscles were considered. In-phase common fluctuations, termed common drive, were observed in the mean firing rates of motor units within each muscle, consistent with earlier work on other muscles. Common fluctuations were also observed between the firing rates of ECU and ECRL motor units albeit with a variable phase shift. The existence of common drive across synergistic muscles was interpreted as implying that the CNS considers the muscles as a functional unit when they act as synergists. (+info)
Treatment of bone and soft tissue sarcomas of the hand and wrist.
(46/534)
We studied 13 consecutive patients with bone and soft tissue sarcomas of the hand and wrist. Chondrosarcoma, Ewing's sarcoma, synovial sarcoma and epithelioid sarcoma were the most frequent histological diagnoses. Limb-sparing surgery was performed in ten patients but eventually three patients required an amputation. Surgical margins were wide in nine patients and marginal in four. Adjuvant therapy for nine patients consisted of chemotherapy in five and chemotherapy with radiation in four. Local recurrence occurred in two patients with epithelioid sarcoma. There was no significant relationship between surgical margin and local recurrence. Distant metastasis occurred in four patients. The 5-year survival rate was 66%. The mean functional score was 87%. Our study indicates that treatment consisting of resection of these tumours with either a wide margin or a marginal margin followed by adjuvant radiation appeared to be safe and resulted in an acceptable degree of limb function except in the patients with epithelioid sarcoma. (+info)
Internally simulated movement sensations during motor imagery activate cortical motor areas and the cerebellum.
(47/534)
It has been proposed that motor imagery contains an element of sensory experiences (kinesthetic sensations), which is a substitute for the sensory feedback that would normally arise from the overt action. No evidence has been provided about whether kinesthetic sensation is centrally simulated during motor imagery. We psychophysically tested whether motor imagery of palmar flexion or dorsiflexion of the right wrist would influence the sensation of illusory palmar flexion elicited by tendon vibration. We also tested whether motor imagery of wrist movement shared the same neural substrates involving the illusory sensation elicited by the peripheral stimuli. Regional cerebral blood flow was measured with H215O and positron emission tomography in 10 right-handed subjects. The right tendon of the wrist extensor was vibrated at 83 Hz ("illusion") or at 12.5 Hz with no illusion ("vibration"). Subjects imagined doing wrist movements of alternating palmar and dorsiflexion at the same speed with the experienced illusory movements ("imagery"). A "rest" condition with eyes closed was included. We identified common active fields between the contrasts of imagery versus rest and illusion versus vibration. Motor imagery of palmar flexion psychophysically enhanced the experienced illusory angles of plamar flexion, whereas dorsiflexion imagery reduced it in the absence of overt movement. Motor imagery and the illusory sensation commonly activated the contralateral cingulate motor areas, supplementary motor area, dorsal premotor cortex, and ipsilateral cerebellum. We conclude that kinesthetic sensation associated with imagined movement is internally simulated during motor imagery by recruiting multiple motor areas. (+info)
Integrated motor cortical control of task-related muscles during pointing in humans.
(48/534)
A large body of compelling but indirect evidence suggests that the motor cortex controls the different forelimb segments as a whole rather than individually. The purpose of this study was to obtain physiological evidence in behaving human subjects on the mode of operation of the primary motor cortex during coordinated movements of the forelimb. We approached this problem by studying a pointing movement involving the shoulder, elbow, wrist, and index finger as follows. Focal transcranial magnetic stimulation (TMS) was used to measure the input-output (I/O) curves-a measure of the corticospinal pathway excitability-of proximal (anterior deltoid, AD, and triceps brachii, TB) and distal muscles (extensor carpi radialis, ECR, and first dorsal interosseus, 1DI) during isolated contraction of one of these muscles or during selective co-activation with other muscles involved in pointing. Compared to an isolated contraction of the ECR, the plateau-level of the ECR sigmoid I/O curve increased markedly during co-activation with the AD while pointing. In contrast, the I/O curve of AD was not influenced by activation of the more distal muscles involved in pointing. Moreover, the 1DI I/O curve was not influenced by activation of the more proximal muscles. Three arguments argue for a cortical site of facilitation of ECR motor potentials. First, ECR motor potentials evoked by a near threshold TMS stimulus were facilitated when the AD and ECR were co-activated during pointing but not those in response to a near threshold anodal electrical stimulus. Second, the ECR H reflex was not found to be task dependent, indicating that the recruitment gain of the ECR alpha-motoneuron pool did not differ between tasks. Finally, in comparison with an isolated ECR contraction, intracortical inhibition tested at the ECR cortical site was decreased during pointing. These results suggest that activation of shoulder, elbow, and wrist muscles involved in pointing appear to involve, at least in part, common motor cortical circuits. In contrast, at least in the pointing task, the motor cortical circuits involved in activation of the 1DI appear to act independently. (+info)