Increase in conduction velocity in myelinated nerves due to stretch – An experimental verification (original) (raw)
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Bangladesh Journal of Medical Physics, 2019
Analysing published experimental findings this paper revealed that for myelinated nerves the conduction velocity (CV) increases on stretching out of the nerve, which has not been pointed out by anyone before. This apparently contradicts existing concepts since stretching out of a nerve fibre reduces its diameter which is expected to reduce the CV. Besides, the change is reversible and immediate, which cannot be explained with existing knowledge either. In order to explain this anomaly, the present work invoked a new resistance to ion flow between the nerve axon and the extracellular fluid created by interdigitated fingerlike processes of myelin sheaths coming from two sides of a node of Ranvier, analyzing published electron microscopic images. When stretched out, the gaps between the processes increase, decreasing the resistance to ion flow and thereby hastening depolarization, increasing CV in turn. The gaps close immediately on the release of the stretching force because of the pu...
Non-Invasive Evaluation of Nerve Conduction in Small Diameter Fibers in the Rat
Physiology journal, 2013
A novel non-invasive technique was applied to measure velocity within slow conducting axons in the distal extreme of the sciatic nerve (i.e., digital nerve) in a rat model. The technique is based on the extraction of rectified multiple unit activity (MUA) from in vivo whole nerve compound responses. This method reliably identifies compound action potentials in thinly myelinated fibers conducting at a range of 9-18 m/s (Aδ axons), as well as in a subgroup of unmylinated C fibers conducting at approximately 1-2 m/s. The sensitivity of the method to C-fiber conduction was confirmed by the progressive decrement of the responses in the 1-2 m/s range over a 20-day period following the topical application of capsaicin (ANOVA p<0.03). Increasing the frequency of applied repetitive stimulation over a range of 0.75 Hz to 6.0 Hz produced slowing of conduction and a significant decrease in the magnitude of the compound C-fiber response (ANOVA p<0.01). This technique offers a unique opport...
Slowly conducting myelinated fibers in peripheral neuropathy
Muscle & Nerve, 1991
The main component of the compound sensory action potential reflects the activity of large myelinated sensory fibers with diameters of greater than 9 pm. By recording the averaged potential using a needle electrode placed close to the nerve, small late components can be measured. The latency of these late components can be used to calculate minimum conduction velocity (CV); in normal subjects, average minimum CV is 15 m/s, corresponding to conduction in fibers of about 4 pm in diameter. Minimum CV was measured in median, ulnar, and sural nerves of 187 patients with mild to severe neuropathic symptoms. A reduction in minimum CV was a sensitive measure of peripheral nerve dysfunction, often showing abnormalities when measures derived from the main component were normal. Patients with isolated abnormalities in minimum CV tended to have neuropathic symptoms but no signs of neuropathy. In addition, reduced minimum conduction velocity has implications for the pathology of different types of neuropathy. Slowing conducting potentials may originate from regenerating fibers, which may be of particular relevance in patients with neuropathic pain.
Does the conduction velocity distribution change along the nerve?
Medical Engineering & Physics, 2004
Nerve conduction velocity distribution (CVD) is a very useful tool to examine the state and function of nerves. Only one record of compound action potential (CAP) may be sufficient to determine the CVD if the shape functions of the single fiber action potentials (SFAP) of fibers are known. Otherwise, CAP recordings from different locations are necessary to determine CVD. In this case, we confront the problem of whether the shape of the CVD changes along the nerve, because many methods that attempt to determine the CVD are based on the assumption that the CVD is invariant along the nerve. There is not a complete solution to this problem, but there are many suggestions allied with the recording conditions to minimise this effect. The other effect that may influence both shapes of CAP and CVD along the nerve is the volume conductor effect. If a suitable model could isolate and eliminate the volume conductor effect, then the spatial variation of CVD may be attributed to the natural conditions of the nerve. In this study, we followed a procedure to eliminate volume conductor effect and then applied our previously published model to examine the spatial variations in CVD. The results show that CVDs estimated at discrete points along the nerve trunk have significantly different patterns. Consequently, it may be concluded that CVD is not uniform along an isolated nerve trunk contrary to the assumptions of the most CVD estimation methods.
In vivo measurement of conduction velocities in afferent and efferent nerve fibre groups in mice
Physiological research / Academia Scientiarum Bohemoslovaca, 2012
Electrophysiological investigations in mice, particularly with altered myelination, require reference data of the nerve conduction velocity (CV). CVs of different fibre groups were determined in the hindlimb of anaesthetized adult mice. Differentiation between afferent and efferent fibres was performed by recording at dorsal roots and stimulating at ventral roots, respectively. Correspondingly, recording or stimulation was performed at peripheral hindlimb nerves. Stimulation was performed with graded strength to differentiate between fibre groups. CVs of the same fibre groups were different in different nerves of the hindlimb. CVs for motor fibres were for the tibial nerve (Tib) 38.5±4.0 m/s (Agamma: 16.7±3.0 m/s), the sural nerve (Sur) 39.3±3.1 m/s (12.0±0.8 m/s) and the common peroneal nerve (Per) 46.7±4.7 m/s (22.2±4.4 m/s). CVs for group I afferents were 47.4±3.1 m/s (Tib), 43.8±3.8 m/s (Sur), 55.2±6.1 m/s (Per) and 42.9±4.3 m/s for the posterior biceps (PB). CVs of higher thres...
Reference data for ulnar nerve short segment conduction studies at the elbow
Muscle & Nerve, 2011
Introduction: The aim of this study was to generate reference data for ulnar nerve short segment conduction studies (SSCSs) at 2-cm intervals. Methods: Ulnar nerve SSCS data were collected from dominant and non-dominant arms of 200 healthy volunteers. The effects of age, gender, weight, height, and body mass index (BMI) on SSCSs were also investigated. Results: High percentile values for short segment latency changes varied from 0.4 to 0.7 ms. Ulnar nerve conductions were slower in the segments 2 cm below and above the elbow compared with the other segments. The amplitude was found not to decrease by >15% in subsequent short segments. There were no significant effects of age and gender on the SSCS parameters. Conductions over the short segments tended to be faster as BMI increased. Conclusions: Reference values should be determined separately over each 2-cm segment, and the effect of BMI should be considered when interpreting SSCSs.
Clinical Neurophysiology, 2006
Objective: To study physiological changes of the compound muscle action potential (CMAP) obtained from stimulation at different sites over the full length of a motor nerve and to study possible effects of anthropometrical factors. Methods: Multicentre study of ulnar motor nerve conduction in five segments to Erb's point performed bilaterally on 100 healthy subjects aged 17-83 years. Results: CMAP amplitude decreased linearly with conduction distance (0.31%/cm) from wrist to Erb's point. CMAP area decreased with the square of conduction distance. Decrease in area was smaller than decrease in amplitude especially distally. CMAP duration increased linearly (0.17%/cm). Amplitude decay correlated with age, height and BMI and dispersion correlated with age and height. There were no correlations between area decay and anthropometrical factors. There was no significant inter-examiner variation. Conclusions: Area decay may be preferred to amplitude decay in the evaluation of conduction block over short segments due to smaller physiological changes and independence of anthropometrical factors. The absence of inter-examiner variation indicates that the results are robust and may be used by other laboratories. Significance: This study provides knowledge of physiological changes of CMAP parameters that may be of importance in the evaluation of nerve pathology, in particular conduction block.
Journal of Orthopaedic …, 2002
Using an animal model, the in vivo visco-elastic properties of peripheral nerve in continuity were examined. The nerves were stretched by either 1 cm -Group A (8.8'%, strain) or 1 cm -Group B (16.1% strain). At constant strain, the stress-relaxation curves were plotted. Maximal relaxation was observed in the first 30 min. After 1 h, the decrease in tensions in Groups A and B were 36.8%) and 41.8'!,:1, respectively. Throughout this hour and for 30 min after the release of tension, regular recordings of nerve blood flow using laser doppler flowmetry and peak nerve conduction velocity were taken. Nerve blood flow was reduced by similar amounts (Group A, 70%; Group B, 78%) by application of traction. On release, however, Group A displayed a reactive hyperaemia (blood flow 151"/0 starting value) while Group B failed to recover (50%) starting value at 30 min). Peak nerve conduction velocity was not significantly altered in Group A in response to traction, whereas in Group B the result was a gradual, but significant reduction in peak velocity to 66% starting value. The lack of correlation between blood flow and peak nerve conduction velocity in these studies suggests that ischaemia is not solely responsible for the increased latency.
A Quantitative Investigation on the Peripheral Nerve Response within the Small Strain Range
Applied Sciences
Peripheral nerves are very complex biological structures crucial to linking the central nervous system to the periphery of the body. However, their real behaviour is partially unknown because of the intrinsic difficulty of studying these structures in vivo. As a consequence, theoretical and computational tools together with in vitro experiments are widely used to approximate the mechanical response of the peripheral nervous tissue to different kind of solicitations. More specifically, particular conditions narrow the mechanical response of peripheral nerves within the small strain regime. Therefore, in this work, the mechanical response of nerves was investigated through the study of the relationships among strain, stress and displacements within the small strain range. Theoretical predictions were quantitatively compared to experimental evidences, while the displacement field was studied for different values of the tissue compressibility. This framework provided a straightforward c...