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Amplitude of the F wave: a potential means of documenting spasticity
Abstract:
The amplitude of 32 averaged F responses (F32) recorded with surface electrodes was 1 percent of the amplitude of the M wave. The largest F response (Fmax) was 4.5 percent of the M wave. In spasticity, Fmax did not increase in amplitude but became more persistent, resulting in a significant increase of F32. There was a positive correlation between the amplitude of F32 and the M wave, and this relationship was abnormal in 60 percent of the studies of patients with spasticity.
Insights
In spasticity, F-wave persistence increased, significantly raising averaged F-wave amplitude (F32) despite no change in the largest F-wave (Fmax). This altered F-wave response correlated abnormally with M-wave amplitude in most patients.
Area of Science:
- Neurophysiology
- Clinical Electrophysiology
Background:
- F-wave analysis is crucial for assessing motor neuron excitability.
- Spasticity is characterized by exaggerated muscle stretch reflexes.
- Understanding F-wave alterations in spasticity can reveal underlying neurophysiological changes.
Purpose of the Study:
- To investigate the characteristics of F-waves in patients with spasticity.
- To determine if F-wave amplitude or persistence is altered in spasticity.
- To explore the relationship between F-wave parameters and M-wave amplitude in spasticity.
Main Methods:
- Surface electrodes were used to record F-responses and M-waves.
- The amplitude of the largest F-response (Fmax) and 32 averaged F-responses (F32) were measured.
- F-wave amplitudes were compared to M-wave amplitudes.
- The correlation between F32 and M-wave amplitude was analyzed in patients with spasticity.
Main Results:
- The amplitude of F32 was 1% of the M-wave amplitude, and Fmax was 4.5% of the M-wave amplitude.
- In spasticity, Fmax amplitude did not increase, but F-waves became more persistent.
- This increased persistence led to a significant rise in F32 amplitude.
- A positive correlation between F32 and M-wave amplitude was observed, which was abnormal in 60% of spasticity patients.
Conclusions:
- Increased F-wave persistence, not amplitude, is a key feature in spasticity.
- The relationship between averaged F-wave and M-wave amplitudes is frequently abnormal in spasticity.
- These findings suggest altered motor neuron excitability contributes to spasticity.