[Effects of ischemia on peripheral nerve evoked potential. Experimental and clinical study]

The association between impaired circulation and peripheral nerve disorders has been recognized for many years. Although many experimental and clinical studies have been carried out on the "ischemic neuropathy", the routine examination to certify it may have not yet been established. Peripheral nerve evoked potential measurement has been used to evaluate the function of the peripheral nerve directly. Some electrophysiological findings concerning nerve ischemia were reported. Most authors reported decreased amplitude, slowed conduction rate, and increased refractory period. But a transient increase in amplitude during ischemia is a characteristic phenomenon in the peripheral nerve as well as in spinal cord evoked potential, as reported by the author previously. Since the purpose ot this study was whether this phenomenon could be a indicator of some kind of pathological condition of the peripheral nerve, experimental and clinical studies were designed to obtain the conditions required for the observation of this phenomenon and to establish a practical method for the differentiation of ischemic neuropathy from other ones. Twenty cats were used in the experimental study. The blood supply to the nerve was controlled by tightening a noose around the base of the ascending aorta. In the clinical studies, sixteen healthy subjects 11 diabetics, 3 patients with arteriosclerosis obliterans, and 3 patients with malignant RA were examined. Since a transient reduction in threshold was observed during ischemia simultaneously with a transient augmentation in amplitude, the latter was assumed to be due to the former. In the animal experiment, the amplitude did not increase further even during complete obstruction of the ascending aorta following a 10-minute partial obstruction of the blood supply. In the clinical studies, the augmentation of amplitude during ischemia was statistically higher in healthy persons than in the patients mentioned above. The requisites for observing the transient augmentation in amplitude were: (1) complete ischemia of the peripheral nerve; optimally ten minutes of ischemia, (2) submaximal stimulation; optimally the strength of stimulation with which the amplitude of the evoked potential became 1/3 of the maximum and (3) maintenance of the blood supply to the peripheral nerve before ischemia. The nerve should not be ischemic before complete ischemia or application of the tourniquet.(ABSTRACT TRUNCATED AT 400 WORDS)