Neurophysiological effects of prolonged cooling of the calf in patients with complete spinal transection.

The neurophysiological effects of prolonged cooling were examined in seven patients with complete spinal lesions. The twitch tension of the soleus muscle, the direct (M-wave) and relfex (H-wave) response to electrical stimulation of the popliteal nerve, the Achilles tendon reflex (ATR) and the degree of inhibition of the H-wave by muscle vibration were recorded before and after a minimum of forty-five minutes cooling of the calf. Changes in the configuration of the M-wave occurred, suggesting that cooling results in slowing of conduction in muscle or motor nerve fibers. Prolongation of the twitch contraction and half relaxation time was observed, implying that the contractile mechanism of the muscle is affected. A significant decrease in the ATR/M ratio was observed, indicating that cooling, in addition, affects the muscle spindle or its connections. No significant alterations in the H/M ratio or in the degree of suppression of the H-wave by vibration were observed.