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

Background It has been shown that progressive neuromuscular blockade (NMB) affects the electromyogram power spectrum and compound muscle action potent ial duration in skeletal muscle. These measures are Linked to the mean musc le action potential conduction velocity (APCV), but no studies have confirm ed a relation between the mean APCV and NMB. The aim of this study was to d etermine whether diaphragm mean APCV is affected by NMB., Methods: The effects of NMB on diaphragm mean APCV were evaluated in five m ongrel dogs. Progressive NMB was induced by slow intravenous infusion of at racurium. During spontaneous breathing, the diaphragm mean APCV was determi ned by electromyogram signals, In the time and frequency domains. The magni tude of NMB was quantified by the amplitude of the compound muscle action p otential and by changes in muscle shortening during supramaximal stimulatio n of the phrenic nerve. Results: Progressive NMB was associated with a decrease in diaphragm mean A PCV. 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 wit hin the diaphragm in an orderly manner, and the blockade first affects musc le fibers with high APCV before it affects fibers with lower APCV.