Anodal block in F-wave studies.
OBJECTIVE
To determine whether F-wave results differ with the anode proximal or distal to the cathode, ie, if clinical anodal block exists.


METHODS
Prospective study of 30 healthy volunteers undergoing nerve conduction and F-wave studies in one median nerve. A needle cathode electrode was used with a surface anode placed alternately proximal and distal to the cathode. The same electromyographer performed all studies with a Dantec Counterpoint machine.


RESULTS
F-wave latencies were essentially unaffected by distal versus proximal positioning. Minimum, maximum, and mean F-wave latencies correlated extremely highly (r=.973 to .988). For both F-wave and M-response latencies and amplitudes, differences between mean values obtained using the two methods were extremely small and were neither clinically nor statistically significant. The frequency of elicitation of F-waves may (p < .05) have been slightly (3.5%) lower when the anode was in the distal position.


CONCLUSIONS
Anodal block is not seen in F-wave studies when using needle electrode stimulations. Reversing the stimulator does not seem to be required. Further study with surface stimulating electrodes is underway to confirm results.
Kirshblum
S
S
Spinal Cord Injury Services, Kessler Institute for Rehabilitation, West Orange, NJ, USA.
Cai
P
P
Johnston
M V
MV
Shah
V
V
O'Connor
K
K
D000328:Adult; D004558:Electric Stimulation; D004566:Electrodes; D004576:Electromyography; D005260:Female; D006801:Humans; D008297:Male; D008475:Median Nerve / Q000502:physiology*; D008875:Middle Aged; D009046:Motor Neurons / Q000502:physiology; D018482:Muscle, Skeletal / Q000294:innervation*; D009431:Neural Conduction / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology; D012016:Reference Values