Ratio of maximum H reflex to maximum M response as a measure of spasticity.

The clinical investigation of the nature and treatment of spasticity has been greatly impeded by the lack of any simple and precise method of measurement of the increased resistance to passive movement of the limbs, most investigators relying on arbitrary clinical grading of severity. Elaborate methods of measurement are still in an experimental stage and are not universally available (Timberlake, 1965; Erdman and Heather, 1965). Angel and Hofmann (1963) therefore explored the possibility of using the ratio between the maximum H reflex and the maximum M response as a simple and precise method of measurement. The M response (Magladery and Mc-Dougal, 1950) is simply the response of a muscle as recorded electromyographically (E.M.G.) to stimulation of the motor nerve. The H reflex was first described by Hoffmann (1918) and its general characteristics have been reviewed in detail by Mayer and Mawdsley (1965). There is general agreement that the major component is a monosynaptic reflex elicited by submaximal stimulation of a mixed motor and sensory nerve and, in a normal adult, it can usually only be elicited in the triceps surae from stimulation of the medial popliteal nerve. In many respects the reflex resembles the ankle jerk with the important difference that the peripheral receptor organs are not involved, fast-conducting afferent fibres being stimulated directly. The H reflex is usually increased in a spastic lower limb while the M response is unaffected. Both responses can be elicited using the same stimulating and recording electrodes and, for purposes of comparison, it is essential that they should be so. Pinelli and Valle (1960) had found the relationship between the height of the two responses at different stimulus strengths and between different individuals to be so variable that they rejected the H/M ratio as a measure of spasti-city. Angel and Hofmann (1963) hoped that by using the ratio between the height of the maximum H reflex and that of the maximum M response the effect of such factors as electrode placement, thickness of skin and, in particular, stimulus strength, might be excluded. They did not, in fact, demonstrate that with different electrode placements a constant ratio could be obtained during the period of the experiment, nor did they clearly establish that an investigation of purely monosynaptic reflex stimulation of the motor pool could provide a valid index of the complex phenomenon of spasticity. Nevertheless, the method was simple and ingenious and might well have …