Evaporative heat loss insufficient to attain heat balance at rest in individuals with a spinal cord injury at high ambient temperature

The aim of the study was to determine whether climatic limits for achieving heat balance at rest are affected by spinal cord injury (SCI). Twenty-three males (8 able-bodied (AB), 8 with paraplegia (PP) and 7 with tetraplegia (TP)) rested in 37°C and 20% relative humidity (RH) for 20 mins. With the ambient temperature held constant, RH was increased by 5% every 7 mins, until gastrointestinal temperature (Tgi) showed a clear inflection or increased by >1°C. Tgi, skin temperatures, perceptual responses and metabolic energy expenditure were measured throughout. Metabolic heat production (AB: 123 (21) W, PP: 111 (15) W, TP: 103 (29) W) and required rate of evaporative cooling for heat balance (Ereq, AB: 113 (20) W, PP: 107 (17) W, TP: 106 (29) W) were similar between groups (p = 0.22 and p = 0.79). Compared to AB, greater increases in Tgi were observed in TP (p = 0.01), with notable increases in mean skin temperature (Tsk) for TP and PP (p = 0.01). A Tgi inflection point was demonstrated by 7 AB, only 3 out of 8 PP and none of TP. Despite metabolic heat production (and Ereq) being similar between groups evaporative heat loss was not large enough to obtain heat balance in TP, linked to a shortfall in evaporative cooling potential. Although PP possess a greater sweating capacity, the continual increase in Tgi and Tsk, in most PP, while lower than for TP, implies that latent heat loss for PP is also insufficient to attain heat balance.