Noninvasive Invastigation of Excitability Parameters of the Finger Branches of Median Nerve by Threshold Tracking Method

Abstract

To provide a basis for basic and clinical studies, we aimed to establish the excitability properties of thumb, index and medius fingers innervated by median nerve by using threshold tracking methods from both right and left hands of right-handed volunteers. In addition to that, possible differences were investigated between the fingers of left and right hands. Experiments were performed on 21 right-handed healthy volunteers. The protocols of threshold tracking method were applied to all subjects. To conduct excitability measurements, median nerve was stimulated at elbow, then non-invasive muscle compound action potential recordings were performed from medius, index and thumb fingers of left and right hand with ring-shaped electrodes. During an experiment, threshold electrotonus, recovery cycle, threshold current stimulus-response relationship and the amount of threshold charge-stimulus duration relationship curves were plotted. Some of the excitability parameters such as refractoriness (%) at 2 ms, strength duration time constant (ms), resting current-voltage (I-V) slope, rheobase and 50% stimulus intensity required to have the maximal response (mA) did not differ significantly (p <0.05) for three fingers of left and right hand. The stimulus-response, strength-duration relationship, 40% threshold electrotonus, current-threshold relationship and recovery cycle curves were obtained. For all of these curves, there were no significant difference (p < 0.05), either. The results showed that there was no statistical significance between the observed fingers. Detailed analysis of these curves also indicated that the activities of all fast, slow and rectifier K+ channels in the membrane of median nerve that innervate finger muscles were similar. Similarly, no significant differences were seen for activity of Na+ channels