Evaluation of the presynaptic inhibition by comparing the amplitudes of H reflexes and F waves. Is it possible?

The H reflexes depend on presynaptic inhibition, but not the F waves. The aim of this study was to explore the possibility for using the comparison of F wave and H reflex amplitudes (F/H ratio) for indirect evaluation of the presynaptic inhibition. An examination of 130 patients with old spastic hemiparesis was performed. The neurophysiological examination included F wave evaluation after stimulation of the tibial nerve, evaluation of soleus H reflex maximal amplitude before (Hmax) and after vibration (Hvibr) applied on the Achilles tendon. The Hvibr/Hmax and F/H amplitude ratios were calculated. Our data revealed that the F/H amplitude ratio is quite different from the Hvibr/Hmax amplitude ratio widely used for evaluation of the presynaptic inhibition. In conclusion comparison of F wave and H reflex amplitudes for indirect evaluation of the presynaptic inhibition is not a valid tool. The differences between H reflexes and F waves do not concern only the presynaptic inhibition.