TY - JOUR
T1 - Strength-duration properties and their voltage dependence at different sites along the median nerve
AU - Mogyoros, Ilona
AU - Lin, Cindy
AU - Dowla, Shareef
AU - Grosskreutz, Julian
AU - Burke, David
N1 - Funding Information:
This work was supported by the National Health and Medical Research Council of Australia and GlaxoWellcome Australia Ltd. Julian Grosskreutz was supported by the Deutsche Forschungsgemeinschaft, Germany.
PY - 1999/9/1
Y1 - 1999/9/1
N2 - Objectives: There is some evidence that the ease with which ectopic activity can be induced varies systematically along the course of a nerve and is greater at more proximal sites. Recent studies have implicated a non-inactivating threshold conductance, possibly due to persistent Na+ channels, in ectopic activity associated with ischaemia and hyperventilation. This conductance is largely responsible for the voltage dependence of strength-duration time constant (τ(SD)), and changes in it can explain the time constant changes that occur during hyperventilation and ischaemia. Methods: To determine whether the strength-duration properties of motor axons of the median nerve vary along the course of the nerve, τ(SD) and rheobase were calculated at wrist, elbow and axilla in 15 healthy subjects, and the relationship of these properties to threshold was assessed using DC polarizing current to change axonal excitability. Results: τ(SD) was similar at the 3 stimulating sites but increased less at the axilla with depolarizing current. Conclusions: These data indicate that the greater tendency for ectopic activity to arise from proximal segments of motor axons cannot be explained by differences in the conductances that contribute to τ(SD) and underlie its dependence on axonal excitability. The findings provide further support for the view that the precise relationship of the stimulating electrodes to the nerve has little effect on τ(SD), at least when it is measured in the forearm.
AB - Objectives: There is some evidence that the ease with which ectopic activity can be induced varies systematically along the course of a nerve and is greater at more proximal sites. Recent studies have implicated a non-inactivating threshold conductance, possibly due to persistent Na+ channels, in ectopic activity associated with ischaemia and hyperventilation. This conductance is largely responsible for the voltage dependence of strength-duration time constant (τ(SD)), and changes in it can explain the time constant changes that occur during hyperventilation and ischaemia. Methods: To determine whether the strength-duration properties of motor axons of the median nerve vary along the course of the nerve, τ(SD) and rheobase were calculated at wrist, elbow and axilla in 15 healthy subjects, and the relationship of these properties to threshold was assessed using DC polarizing current to change axonal excitability. Results: τ(SD) was similar at the 3 stimulating sites but increased less at the axilla with depolarizing current. Conclusions: These data indicate that the greater tendency for ectopic activity to arise from proximal segments of motor axons cannot be explained by differences in the conductances that contribute to τ(SD) and underlie its dependence on axonal excitability. The findings provide further support for the view that the precise relationship of the stimulating electrodes to the nerve has little effect on τ(SD), at least when it is measured in the forearm.
UR - http://www.scopus.com/inward/record.url?scp=0032847145&partnerID=8YFLogxK
U2 - 10.1016/S1388-2457(99)00087-5
DO - 10.1016/S1388-2457(99)00087-5
M3 - Journal articles
C2 - 10479029
AN - SCOPUS:0032847145
SN - 1388-2457
VL - 110
SP - 1618
EP - 1624
JO - Clinical Neurophysiology
JF - Clinical Neurophysiology
IS - 9
ER -