Muscle membrane polarisation after provocative tests, and after cooling: the normal CMAP changes to be expected.
OBJECTIVE
To know the range of changes of compound muscle action potentials (CMAPs) in the muscles innervated by the ulnar nerve after diverse provocative tests, 14 healthy patients were studied with the same protocol.


METHODS
CMAPs were measured at rest, just after a short exercise test (SET), during short 5 and 10c/s repetitive nerve stimulation (RNS) trains, at approximately 32 and approximately 20 degrees C.


RESULTS
At 32 degrees C, the SET induced a significant but transient enlargement of the CMAPs (amplitude increased by 8.3%, duration decreased by 9%) that was only partially reproduced by RNS trains, except for a significant shortening of the CMAPs at 10c/s. At 20 degrees C without exercise, CMAPs increased significantly by approximately 30% in amplitude, duration and area, and after the SET the inverse of what has been seen at 32 degrees C was observed (amplitude decreased by 1.7% and duration increased by 9%). RNS at 20 degrees C produced a marked interpatient heterogeneity except for a significant shortening of the CMAPs at 10c/s. In one pure autonomic failure patient, the infusion of norepinephrine induced potentiation of the responses at rest and a decrease in the expected changes after provocative tests.


CONCLUSIONS
CMAP amplitude and duration are significantly modified just after the SET at 32 degrees C, at rest at 20 degrees C and after RNS at 10c/s but not at 5c/s. Although providing indirect evidence, these findings indicate that provocative tests make the muscle membrane hyperexcitable by the way of a direct influence on the electrical events and by an indirect local catecholamine spillover.
Kuntzer
Thierry
T
Service de Neurologie, Centre Hospitalier Universitaire Vaudois, rue du Bugnon, CHUV BH 07/306, 1011 Lausanne, Switzerland. thierry.kuntzer@chuv.hospvd.ch
Michel
Patrik
P
D000200:Action Potentials / Q000502:physiology*; D000328:Adult; D001342:Autonomic Nervous System Diseases / Q000503:physiopathology; D002462:Cell Membrane / Q000502:physiology*; D003080:Cold Temperature; D004558:Electric Stimulation; D004576:Electromyography; D015444:Exercise / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000294:innervation*; D014459:Ulnar Nerve / Q000502:physiology*