Neurophysiologic responses of peripheral nerve to anoxia: Effects of hypothermia and age

ObjectiveQuantify how temperature and age modulate the effects of multiple periods of anoxia on peripheral nerve.MethodsNerve action potentials (NAP) recorded from rat sciatic nerve in vitro. Effects of multiple cycles of anoxia on the NAP are evaluated as functions of temperature and age. In some experiments, the nerve was held at constant temperature and others the nerve was hypothermic only during anoxia and returned to 36 °C with restoration of oxygen.ResultsHypothermia mitigates the effect of anoxia on the NAP, an effect that increases with multiple cycles of anoxia. Preservation of the NAP waveform after 5 cycles of anoxia is best when hypothermia is delivered only during anoxia. Hypothermia reduces the rate at which the NAP disappears during anoxia but has a limited effect on the rate of recovery. With intermittent hypothermia the amplitude of the NAP is best preserved with temperatures of 15–22 °C. Velocity and duration are best preserved below 25 °C. The loss of the NAP during anoxia is slower in the older nerves.ConclusionsLower temperatures improve the recovery of the NAP from anoxia and increase the time it takes for the NAP to disappear during anoxia as does increasing age.SignificanceDocument the effects of hypothermia on the anoxia response as a step toward understanding its nerve protectant effect.

► Temperature modulates the effect of anoxia with hypothermia only during anoxia producing better recovery to baseline than constant hypothermia. ► The effects of age on the response of the nerve to temperature and anoxia are relatively small and mainly confined to increases in the time to disappearance of the NAP during anoxia in older nerves. ► Hypothermia has two different effects on the preservation of the NAP: amplitude is optimally preserved at roughly 17 °C while the velocity/duration are optimally preserved at temperatures below roughly 22 °C.