Studies in man and cat of the significance of the H wave

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Abstract
A study was made of H waves recorded from the calf muscles in 20 adult subjects without spinal cord or peripheral nerve dysfunction, patients with peripheral nerve abnormalities and 20 adult cats. Results showed that the H wave is reflex in origin. It has a monosynaptic linkage through large fibers and a polysynaptic linkage through small fibers. The H wave can easily be recorded in other muscles. Conduction velocities in the fast afferrent and efferent fibers are the same and indicate that the monosynaptic discharge is via the large fibers, 13-14 micra in diameter. The conduction velocity in these fibers was reduced in patients with peripheral neuropathies. Alterations in the H-wave response could be used in estimating disturbances of the proximal conduction in peripheral neuropathies and altered motor neuron excitability in upper motor neuron lesions.