Temporospatial effects on orthodromic sensory potential propagation during ischemia

Abstract

Sensory potentials recorded at two to four sites along the median nerve during ischemia in normal subjects were analyzed with respect to the effects of conduction distance and duration of ischemia. Latency increased rectilinearly with the squared duration of ischemia in minutes, and the rate of the latency increase along the nerve was a power of the preischemic latency, a measure of conduction distance. This finding indicates a temporospatial slowing of sensory conduction velocity of ischemic nerves. Calculated latencies fitted with measured values within +/- 0.2 msec in 95% of 385 recordings. The compound potential amplitude decreased exponentially with the concomitant increase in temporal dispersion, which was the major cause for the decrease in amplitude during the first 20 minutes of ischemia. The nerve conduction pattern during ischemia may serve as a model for biochemical axon membrane dysfunction, a possible factor in the pathogenesis of toxic-metabolic neuropathies.

Why Are Sensory Axons More Vulnerable for Ischemia than Motor Axons?

“…Fifth, we cannot completely exclude the effects of temporal dispersion. It has been found that temporal dispersion is an important factor underlying CSAP amplitude reduction during the first 20 minutes of ischemia [40] and its effects are probably larger on CSAP than on CMAP amplitudes [41]. However, according to figure 1, it seems unlikely that temporal dispersion was a major factor causing the quicker reduction in CSAP amplitude during ischemia in our study, although we cannot exclude the effects of phase cancellation.…”

Hemodynamic Consideration in Intraoperative Neurophysiological Monitoring in Neuromuscular Scoliosis Surgery

“…Before the demonstration of the effect of ischemic condition on the SEPs along with the posterior column, ischemia had already been revealed to prolong the latency and reduce the amplitude of the peripheral nerves in conduction study [19]. Temporal dispersion was reported to follow after the anoxia in peripheral nerves, and with the previous evidence that the reduction in a single-fiber spike amplitude does not exceed 16%, the major cause of the amplitude reduction in peripheral nerves is explained by temporal dispersion [19][20][21].…”

Electrophysiologic Monitoring during Surgery to Repair the Thoracoabdominal Aorta

“…Similar to the SSEP, ischemia in a peripheral nerve causes the MEP recorded in the muscle to drop over 20 minutes, 15 with more rapid deterioration following ischemia in the spinal grey matter. MEP responses recorded epidurally are sensitive to ischemia but not as sensitive as responses recorded distal to the anterior horn cell, perhaps because the anterior horn has a higher metabolic rate than posterior horn.…”