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Velocity recovery cycles of human muscle action potentials and their sensitivity to ischemia
Author(s) -
Z'Graggen Werner J.,
Bostock Hugh
Publication year - 2009
Publication title -
muscle and nerve
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.025
H-Index - 145
eISSN - 1097-4598
pISSN - 0148-639X
DOI - 10.1002/mus.21192
Subject(s) - depolarization , refractory period , membrane potential , medicine , anesthesia , stimulation , compound muscle action potential , electrophysiology , brachioradialis , chemistry , interstimulus interval , neuroscience , endocrinology , biophysics , anatomy , biology , forearm
This study was undertaken to test whether recovery cycle measurements can provide useful information about the membrane potential of human muscle fibers. Multifiber responses to direct muscle stimulation through needle electrodes were recorded from the brachioradialis of healthy volunteers, and the latency changes measured as conditioning stimuli were applied at interstimulus intervals of 2–1000 ms. In all subjects, the relative refractory period (RRP), which lasted 3.27 ± 0.45 ms (mean ± SD, n = 12), was followed by a phase of supernormality, in which the velocity increased by 9.3 ± 3.4% at 6.1 ± 1.3 ms, and recovered over 1 s. A broad hump of additional supernormality was seen at around 100 ms. Extra conditioning stimuli had little effect on the early supernormality but increased the later component. The two phases of supernormality resembled early and late afterpotentials, attributable respectively to the passive decay of membrane charge and potassium accumulation in the t‐tubules. Five minutes of ischemia progressively prolonged the RRP and reduced supernormality, confirming that these parameters are sensitive to membrane depolarization. Velocity recovery cycles may provide useful information about altered muscle membrane potential and t‐tubule function in muscle disease. Muscle Nerve, 2008