Sleutjes BTHM, Ruisch J, Nassi TE, Buitenweg JR, van Schelven LJ, van den Berg LH, Franssen H, Stephan Goedee H. Impact of stimulus duration on motor unit thresholds and alternation in compound muscle action potential scans.
Clin Neurophysiol 2021;
132:323-331. [PMID:
33450554 DOI:
10.1016/j.clinph.2020.10.026]
[Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2020] [Revised: 09/30/2020] [Accepted: 10/26/2020] [Indexed: 11/17/2022]
Abstract
OBJECTIVE
To investigate the impact of stimulus duration on motor unit (MU) thresholds and alternation within compound muscle action potential (CMAP) scans.
METHODS
The stimulus duration (0.1, 0.2, 0.6, and 1.0 ms) in thenar CMAP scans and individual MUs of 14 healthy subjects was systematically varied. We quantified variability of individual MU's thresholds by relative spread (RS), MU thresholds by stimulus currents required to elicit target CMAPs of 5% (S5), 50% (S50) and 95% (S95) of the maximum CMAP, and relative range (RR) by 100*[S95-S5]/S50. We further assessed the strength-duration time constant (SDTC). Experimental observations were subsequently simulated to quantify alternation.
RESULTS
RS, unaffected by stimulus duration, was 1.65% averaged over all recordings. RR increased for longer stimulus duration (11.4% per ms, p < 0.001). SDTC shortened with higher target CMAPs (0.007 ms per 10% CMAP, p < 0.001). Experiments and simulations supported that this may underlie the increased RR. A short compared to long stimulus duration recruited relative more MUs at S50 (more alternation) than at the tails (less alternation).
CONCLUSIONS
The stimulus duration significantly affects MU threshold distribution and alternation within CMAP scans.
SIGNIFICANCE
Stimulation settings can be further optimized and their standardization is preferred when using CMAP scans for monitoring neuromuscular diseases.
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