Velocity recovery cycles of human muscle action potentials: Repeatability and variability

Muscle velocity recovery cycles: Effects of repetitive stimulation on two muscles

“…We assessed the reliability of VRC measurements at rest and during activation between 2 investigation centers and demonstrated that the excitability parameters were consistent between the centers (i.e., between investigators). Altogether, these findings combined with the previously published repeatability study (same subjects recorded twice by the same investigator)12 further confirm the validity of the technique. These findings, therefore, indicate that it is reasonable to combine muscle excitability studies in multi‐center clinical trials, which may be particularly useful in the study of rare muscle disorders.…”

“…The CMAPs are recorded by means of surface electrodes and result from stimulation of the motor nerve. In contrast, direct stimulation of the muscle fibers5, 6, 11 bypasses the neuromuscular junction and provides an assessment of muscle properties alone. Furthermore, electrically evoked stimulation presents several advantages: (i) it can be easily standardized; (ii) it is not influenced by the motivation of the subjects or patients; and (iii) it does not require patient cooperation and can, therefore, be applied in intensive care.…”

“…First it was found that muscle VRCs were altered in patients with chronic renal failure in a way that suggested membrane depolarization. The changes were related to hyperkalemia which was only transiently reversed by dialysis 5. More recently it was found that muscle excitability was also altered in patients with critical illness myopathy, as evidenced by a prolonged MRRP and a reduced ESN, which were interpreted as evidence of membrane depolarization and/or increased sodium channel inactivation 6…”

“…This study was undertaken to test the feasibility of extending the method to increase its sensitivity to muscle pathology. The original method,3 which was used unchanged in the first 2 clinical studies,5, 6 was, therefore, modified in several ways. First, we recorded VRCs with a train of 5 conditioning stimuli (in addition to 1 and 2 conditioning stimuli) to increase the late component of supernormality.…”

“…Furthermore, because some muscle disorders preferentially affect the lower limb, we compared the recordings from BR with those from tibialis anterior (TA), which has previously been found to be suitable for measurements of conduction velocity by direct muscle stimulation 11. Finally, we have previously provided evidence of satisfactory repeatability of VRC recordings within subjects 12. We have now compared recordings on the same muscle in different subjects at different investigation centers (London and Bern), to test whether they would be sufficiently consistent to combine in a multi‐center study.…”