Effects of Temperature on Adaptive Processes in Simulated Chronic Inflammatory Demyelinating Polyneuropathy at 20°C-42°C

Abstract

The effects of temperature (from 20°C to 42°C) on action and polarizing electrotonic potentials (nodal and internodal) and their current kinetics were previously studied by us in a simulated case of 70% chronic inflammatory demyelinating polyneuropathy (70% CIDP). To complete the cycle of our studies on adaptive processes in this case, the temperature effects on strength-duration time constant, rheobasic current and recovery cycle are investigated. The computations use our temperature dependent multi-layered model of the myelinated human motor nerve fibre and the temperature is increased from 20°C to 42°C. The results show that as the action and polarizing electrotonic potential parameters, these excitability parameters are more sensitive to the hyperthermia (≥40°C) and are most sensitive to the hypothermia (≤25°C), especially at 20°C, than at temperatures in the range of 28°C-37°C. With the increase of temperature from 20°C to 42°C, the strength-duration time constant decreases ~5.2 times, while it decreases ~3.5 times in the physiological range of 28°C-37°C. Conversely, the rheobasic current increases ~3.0 times from 20°C-42°C, while it increases ~1.2 times in the range of 28°C-37°C. As in the normal case, the behavior of axonal superexcitability in the CIDP case is complex in a 100 ms recovery cycle with the increase of temperature. The axonal superexcitability decreases with the increase of temperature during hypothermia and increases with the increase of temperature during hyperthermia, especially at 42°C. However, the superexcitability period in the CIDP case is followed by a late subexcitability period at 37°C only and the recovery cycles are with reduced superexcitability and without relative refractory periods in the range of 20°C-40°C. The present results are essential for the interpretation of mechanisms of excitability parameter changes obtained here and measured in CIDP patients with symptoms of cooling, warming and fever, which can result from alterations in body temperature. They suggest that the adaptive processes in CIDP patients are in higher risk during hypothermia than during hyperthermia.