Effect of Lidocaine Chloride on Group A Nerve Fibers Function

Local anesthetics, such as lidocaine chloride delay or inhibit the occurrence and transmission of impulses along the excitable tissue membranes, but there is not enough information about their effects on types of nerve fibers within the whole nerve. The aim of the study was to determine the function parameters and examine the degree of blocking for each fiber type in group A of isolated frog sciatic nerves in relation to lidocaine chloride concentration. Thirty frog sciatic nerves, divided into three groups of 10, were examined. The nerves were incubated in Ringer solution (2.0 mmol/l calcium solution) for 2 hours and control measurements were made. The nerves were put then in the following lidocaine chloride solutions: group I: 0.5 mmol/l, group II: 1.0 mmol/l and group III: 2.0 mmol/l. Experimental measurements were performed during incubation each minute until response disappearance. The compound action potential was induced by single electrical stimulus and the parameters were measured using the digital oscilloscope. The obtained data were statistically analyzed using the GraphPad Prism 5.0. Conduction velocitities for the respective types of fiber were: Aα = 18.61±1.44 m/s; Aβ = 14.26±1.28 m/s; Aγ = 10.82±1.06 m/s; and Aδ = 6.51±0.51 m/s. The lowest percentage of blocked fiber type was for Aα, and the highest for Aδ in relation to all three concentrations of lidocaine chloride (p≥0.05). Increasing concentrations of lidocaine chloride solution increased the proportion of blocked fibers for each type of group A fibers (p≥0.05). For Aδ fibers decrease of amplitude compared to the decrease of conduction velocity was greater (p≥0.05). All group A fibers were sensitive to the effects of lidocaine chloride, but the most sensitive were Aδ fibers.