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H Reflex (h + reflex)
Selected AbstractsSoleus T reflex modulation in response to spinal and tendinous adaptations to unilateral lower limb suspension in humansACTA PHYSIOLOGICA, Issue 3 2008O. R. Seynnes Abstract Aim:, To investigate the influence of tendinous and synaptic changes induced by unilateral lower limb suspension (ULLS) on the tendon tap reflex. Methods:, Eight young men underwent a 23-day period of ULLS. Muscle cross-sectional area (CSA), torque and electromyographic (EMG) activity of the plantar flexor muscles (normalized to the M wave), Achilles tendon,aponeurosis mechanical properties, soleus (SOL) H and T reflexes and associated peak twitch torques were measured at baseline, after 14 and 23 days of ULLS, and 1 week after resuming ambulatory activity. Results:, Significant decreases in muscle CSA (,9%), in maximal voluntary torque (,10%) and in the associated SOL EMG activity (,16%) were found after ULLS (P < 0.05). In addition to a 36% (P < 0.01) decrease in tendon,aponeurosis stiffness, normalized H reflex increased by 35% (P < 0.05). An increase in the slope (28%, P < 0.05) and intercept (85%, P < 0.05) of the T reflex recruitment curve pointed to an increase in the gain and to a decrease in the sensitivity of this reflex, possibly resulting from the decrease in the tendon,aponeurosis stiffness at low forces. Following ULLS, changes in tendinous stiffness correlated with changes in neuromuscular efficiency (peak twitch torque to reflex ratio) at higher tendon tap forces. Conclusion:, These findings point out the dual and antagonistic influences of spinal and tendinous adaptations upon the tendon tap reflex in humans under conditions of chronic unloading. These observations have potential implications for the sensitivity of the short-latency Ia stretch response involved in rapid compensatory contractions to unexpected postural perturbations. [source] The changes in neuromuscular excitability with normobaric hyperoxia in humansEXPERIMENTAL PHYSIOLOGY, Issue 1 2010Christelle Brerro-Saby Based on previous observations in hyperbaric hyperoxia, we hypothesized that normobaric hyperoxia, often used during general anaesthesia and resuscitation, might also induce a neuromuscular excitability. In heathy volunteers, we studied the consequences of a 50 min period of pure oxygen breathing on the neuromuscular conduction time (CT), the amplitude of the compound evoked muscle potential (M-wave), the latency and amplitude of the Hoffman reflex (H reflex) and the electromyographic tonic vibratory response (TVR) of the flexor digitorum superficialis muscle to explore the proprioceptive reflex loop. Hyperoxia-induced oxidative stress was measured by the changes in blood markers of lipid peroxidation (thiobarbituric acid reactive substances, TBARS) and antioxidant response (reduced ascorbic acid, RAA). During hyperoxia, the M-wave amplitude increased, both CT and H reflex latency were shortened, and the H reflex amplitude increased. By contrast, TVR significantly decreased. Concomitantly, an oxidative stress was assessed by increased TBARS and decreased RAA levels. This study shows the existence of dual effects of hyperoxia, which facilitates the muscle membrane excitability, nerve conduction and spinal reflexes, but reduces the gain of the proprioceptive reflex loop. The activation of the group IV muscle afferents by hyperoxia and the resulting oxidative stress might explain the TVR depression. [source] Caffeine increases spinal excitability in humansMUSCLE AND NERVE, Issue 3 2003C. Walton MSc Abstract The Hoffman reflex (H reflex) has long been established as a measure of spinal excitability. Caffeine is one of the most widely consumed drugs in the world. Because it is known to increase excitatory neurotransmission, we hypothesized that caffeine would increase spinal excitability and thus alter the H reflex by increasing its amplitude. Seven subjects each attended the laboratory on 2 days. Caffeine (6 mg/kg) was administered on one day and a placebo was administered on the other. The tibial nerve was stimulated at incremental intensities to create an H-reflex recruitment curve prior to capsule administration (pretest) and 1 h later (posttest) on each day. The slope of H-reflex recruitment curve normalized to that of the M wave (Hslp/Mslp) was compared (pretest to posttest). Caffeine increased spinal excitability 43 ± 17% (P < 0.05). Thus, caffeine may be used to safely increase spinal excitability in electrophysiological studies of the human neuromuscular system. Our results also suggest that caffeine intake should be controlled when the H reflex is used in diagnostic and experimental situations. Muscle Nerve 28: 359,364, 2003 [source] Excitability of human muscle afferents studied using threshold tracking of the H reflexTHE JOURNAL OF PHYSIOLOGY, Issue 2 2002Cindy S.-Y. In human peripheral nerves, physiological evidence has been presented for a number of biophysical differences between cutaneous afferents and , motor axons. The differences in strength-duration properties for cutaneous afferents and motor axons in the median nerve have been attributed to greater expression of a persistent Na+ conductance (INa,P) on cutaneous afferents. However, it is unclear whether the biophysical properties of human group Ia afferents differ from those of cutaneous afferents. The present studies were undertaken to determine whether the properties of human group Ia afferents can be studied indirectly using ,threshold tracking' to measure the excitability changes in the H reflex, and to determine whether the excitability of group Ia afferents differs from that of cutaneous afferents. The strength-duration properties of the soleus H reflex and soleus motor axons were measured at rest and during sustained voluntary contractions. Similar experiments were performed on the median nerve at the wrist to study the strength-duration properties of cutaneous afferents, , motor axons and H reflex of the thenar muscles. In addition, the technique of ,latent addition' was used to determine whether there was a difference in a low-threshold conductance on soleus Ia afferent and motor axons. The present findings indicate that the strength-duration time constant (,SD) for the H reflex is longer than that for , motor axons, but similar to that for cutaneous afferents. There were no differences in ,SD for the soleus H reflex at rest and during contractions, suggesting that ,SD for the H reflex is largely unaffected by changes in synaptic or motoneurone properties. Finally, the difference in latent addition suggests that the longer ,SD of the soleus H reflex may indeed be due to greater activity of a persistent Na+ conductance on Ia afferents than on soleus , motor axons. [source] Chronic sensorimotor polyradiculopathy with antibodies to P2: An electrophysiological and immunoproteomic analysisMUSCLE AND NERVE, Issue 1 2008Ricard Rojas-Garcia MD Abstract In this study we report a patient with chronic progressive sensory ataxia, proximal weakness, immunoglobulin M (IgM) monoclonal gammopathy, and elevated protein levels in the cerebrospinal fluid, who showed a good response to prednisone. Electrophysiological study disclosed abnormalities predominantly of late responses (F waves and H reflexes), with no evidence of demyelination in the peripheral nerves, suggesting motor and preganglionic sensory nerve roots as the site of the lesion. An immune-mediated pathogenesis was considered and, to identify possible target antigens, we performed bidimensional electrophoresis and a Western blot study. Based on the suspected lesion site, we used human anterior and posterior root extracts. We identified IgM reactivity against peripheral nerve myelin protein P2. Enzyme-linked immunosorbent assay confirmed IgM reactivity toward one synthetic peptide from P2. To our knowledge, reactivity against P2 has not been reported previously in a paraproteinemic neuropathy. Furthermore, we demonstrated that bidimensional electrophoresis and Western blot of the tissue involved, as determined by clinical and electrophysiological studies, may be useful to establish clinical,immunological correlations in paraproteinemic neuropathies. Muscle Nerve, 2008 [source] Medial dorsal superficial peroneal nerve studies in patients with polyneuropathy and normal sural responsesMUSCLE AND NERVE, Issue 3 2005Mark Kushnir MD Abstract We studied medial dorsal superficial peroneal (MDSP) nerves in 52 patients with clinical evidence of mild chronic sensorimotor polyneuropathy and normal sural nerve responses, in order to assess the diagnostic sensitivity and usefulness of MDSP nerve testing in electrodiagnostic practice. To determine the effect of age on MDSP nerve parameters, 98 normal subjects were also examined. Electrodiagnostic evaluation involved studies of motor nerve conduction in tibial, peroneal, and median nerves; sensory nerve conduction in sural, MDSP, median, and radial nerves; tibial and peroneal nerve F waves; H reflexes from the soleus muscles; and needle electromyography of gastrocnemius and abductor hallucis muscles. Among the patients, 49% had low-amplitude sensory responses in MDSP nerves and 57% had either slowing of sensory conduction velocity or no sensory responses on proximal stimulation. MDSP nerve amplitude, tibial nerve motor velocity, and H reflexes were the most sensitive for detection of mild chronic symmetrical axonal sensorimotor polyneuropathy. MDSP nerve testing should be included in the routine electrodiagnostic evaluation of patients with suspected polyneuropathy and normal sural nerve responses. Muscle Nerve, 2005 [source] Time-varying changes in corticospinal excitability accompanying the triphasic EMG pattern in humansTHE JOURNAL OF PHYSIOLOGY, Issue 3 2000Colum D. MacKinnon 1Nine healthy subjects performed single rapid wrist movements from neutral to targets at 20 deg of flexion or extension in response to an auditory cue. Surface EMG was recorded from the wrist flexors and extensors together with wrist position. Movements in both directions were characterised by the usual triphasic pattern of EMG activity in agonist (AG1), antagonist (ANTAG) and again in agonist (AG2) muscles. 2Single pulses of transcranial magnetic stimulation (TMS) were applied over the motor cortex at an intensity of 80 % of resting threshold at random times between 80 and 380 ms after the cue. We measured the peak-to-peak amplitude of the evoked motor potential (MEP) and the integrated EMG (IEMG) activity that preceded the MEP. In a separate set of experiments H reflexes were elicited in the wrist flexors instead of MEPs. 3MEP amplitudes in the agonist muscle increased by an average of 10 ± 8 ms (range ,1 to 23 ms) prior to the onset of the AG1 burst and were associated with an increase of over sevenfold in the MEP:IEMG ratio, irrespective of movement direction. Agonist H reflex amplitudes were linearly related to, and increased at the same time as, changes in agonist IEMG. 4The principal ANTAG burst was not preceded by an increase in the antagonist muscle MEP:IEMG ratio. No relationship was found between the amplitude of the antagonist H reflexes and the preceding antagonist IEMG. 5Five subjects showed an increase in the MEP:IEMG ratio preceding and during the initial part of the AG2 burst. 6Our method of analysis shows that changes in motor cortical excitability mediating the initiation of movement occur much closer to the onset of EMG activity (less than 23 ms) than the 80,100 ms lead time previously reported. The lack of such changes before the onset of the ANTAG burst suggests that this may be initiated by a different, perhaps subcortical, mechanism. [source] | ||||||||||