Physiological Considerations of Heat Intolerance in People with Multiple Sclerosis

Abstract

Up to 80% of people diagnosed with multiple sclerosis (MS) experience Uhthoff’s phenomenon, which is characterised by a temporary worsening of neurological symptoms and a concomitant onset of fatigue during exercise and/or with exposure to a hot environment. In order to understand the best strategies to mitigate the onset of heat-related MS symptoms and associated fatigue, we need to closer examine the underlying physiological mechanisms responsible for this phenomenon. The purpose of the present thesis was to explore the potential thermo-physiological mechanisms responsible for Uhthoff’s phenomenon in heat-sensitive MS patients during rest and exercise in hot (up to 35°C) environments. Specifically, study 1 sought to determine whether resting core temperature and metabolic rate was elevated in people with relapsing-remitting MS and to assess whether an elevated resting core temperature was associated with subjective measures of physical, cognitive and psychosocial fatigue. Study 2 sought to determine whether a contributing factor to heat intolerance in MS patients, was in part, a greater rise in core temperature by virtue of a blunted thermoregulatory response during exercise in warm (30°C) and hot (35°C) environments. This study measured deep core temperature, alongside sweating and skin blood flow responses in people with relapsing-remitting MS, compared to healthy controls while cycling in climate-controlled chamber. Finally, study 3 assessed whether ingestion of cold-water during exercise in a warm environment could prolong exercise tolerance in heat-sensitive people with MS.