Influence of atracurium on the diaphragm mean action potential conduction velocity in canines

Abstract

Background: It has been shown that progressive neuromuscular blockade (NMB) affects the electromyogram power spectrum and compound muscle action potential duration in skeletal muscle. These measures are linked to the mean muscle action potential conduction velocity (APCV), but no studies have confirmed a relation between the mean APCV and NMB. The aim of this study was to determine whether diaphragm mean APCV is affected by NMB. Methods: The effects of NMB on diaphragm mean APCV were evaluated in five mongrel dogs. Progressive NMB was induced by slow intravenous infusion of atracurium. During spontaneous breathing, the diaphragm mean APCV was determined by electromyogram signals, in the time and frequency domains. The magnitude of NMB was quantified by the amplitude of the compound muscle action potential and by changes in muscle shortening during supramaximal stimulation of the phrenic nerve. Results: Progressive NMB was associated with a decrease in diaphragm mean APCV. At approximately 70% reduction in the compound muscle action potential amplitude, diaphragm mean APCV had decreased more than 20%. Recovery after NMB was characterized by a restoration of the mean APCV to control values. Conclusion: This study shows that progressive NMB paralyzes motor units within the diaphragm in an orderly manner, and the blockade first affects muscle fibers with high APCV before it affects fibers with lower APCV.