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The abductor pollicis brevis R1 response: normative data and physiological behavior
C A De Meulenmeester1, P R Bourque, R C Grondin
1Division of Neurology, Ottawa Civic Hospital, University of Ottawa, Canada.
Electromyography and Clinical Neurophysiology
|July 4, 1998
Summary
The R1 response in the abductor pollicis brevis muscle is reliably measurable during voluntary contraction, offering a potential diagnostic tool for nerve damage in the arm. This electrophysiological technique shows promise for assessing demyelinative lesions.
Area of Science:
- Neurophysiology
- Electromyography
- Clinical Neuroscience
Background:
- H reflexes are difficult to record from resting hand muscles.
- A short latency R1 response, similar to the H reflex, is obtainable from upper extremity muscles during voluntary contraction.
Purpose of the Study:
- To assess the reliability of measuring the R1 response in the abductor pollicis brevis muscle.
- To evaluate the potential clinical utility of the R1 response for diagnosing neurological conditions.
Main Methods:
- Repetitive stimulation of median nerves (3 Hz) at various intensities (threshold, 20%, 40%, 60% M response).
- Recording from the abductor pollicis brevis muscle during minimal and moderate voluntary contraction in 20 healthy subjects.
Main Results:
- The R1 response was consistently present at 40% stimulation intensity during moderate contraction.
- Mean latency was 27 ms, correlating with arm length, and showed low intersubject variability.
- Mean amplitude was 1.17 mV, with greater variability than latency.
Conclusions:
- The abductor pollicis muscle R1 response is reliably measurable, with latency being more consistent than amplitude.
- This technique may aid in assessing demyelinative lesions affecting the brachial plexus and C8-T1 nerve roots.