Independent influence of spinal cord injury level on thermoregulation during exercise

The purpose of this study was to establish the independent influence of SCI level on the change in core temperature and thermoregulatory sweating in athletes with TP (C5-C8), high paraplegia (HP; T1-T5), low paraplegia (LP; T6-L1), and AB controls during exercise in the heat.

At a glance:

• ~50% of the variability in core temperature responses among individuals with paraplegia is explained by injury level.
• There was a reduced individual variability in the core temperature response of individuals with TP whose sweating is completely abolished by injury.
• Central and peripheral control of sweating does not seem to be altered by an SCI in athletes with paraplegia.

Purpose:
This study aimed to establish the true influence of spinal cord injury (SCI) level on core temperature and sweating during exercise in the heat independently of biophysical factors.

Methods:
A total of 31 trained males (8 with tetraplegia [TP; C5-C8], 7 with high paraplegia [HP; T1-T5], 8 with low paraplegia [LP; T6-L1], and 8 able bodied [AB]) performed 3 x 10 min of arm ergometry with 3-min rest at a metabolic heat production of (a) 4.0 W·kg^-1 (AB vs TP) or (b) 6.0 W·kg^-1 (AB vs HP vs LP), in 35°C, 50% relative humidity. Esophageal (T_es) and local skin temperatures and local sweat rate (LSR) on the forehead and upper back were measured throughout.

Results:
Change in T_es was greatest in TP (1.86°C ± 0.32°C vs 0.29°C ± 0.07°C, P < 0.001) and greater in HP compared with LP and AB, reaching 1.20°C ± 0.50°C, 0.66°C ± 0.23°C, and 0.53°C ± 0.12°C, respectively (P < 0.001). Approximately half of the variability in end-trial ΔT_es was described by SCI level in paraplegics (adjusted R² = 0.490, P = 0.005). Esophageal temperature onset thresholds of sweating at the forehead and upper back were similar among HP, LP, and AB, whereas no sweating was observed in TP. Thermosensitivity (ΔT_es vs ΔLSR) was also similar, except for LP demonstrating lower thermosensitivity than AB at the upper back (0.78 ± 0.26 vs 1.59 ± 0.89 mg·cm^-2·min^-1, P = 0.039). Change in skin temperature was greatest in denervated regions, most notably at the calf in all SCI groups (TP, 2.07°C ± 0.93°C; HP, 2.73°C ± 0.68°C; LP, 2.92°C ± 1.48°C).

Conclusion:
This study is the first to show the relationship between ΔT_es and SCI level in athletes with paraplegia after removing variability arising from differences in metabolic heat production and mass. Individual variability in ΔT_es is further reduced among athletes with TP because of minimal evaporative heat loss secondary to an absence of sweating.

Full reference and abstract:
Forsyth, P., Miller, J., Pumpa, K., Thompson, K. & Jay, O. Independent influence of spinal cord injury level on thermoregulation during exercise. Medicine and Science in Sports and Exercise. 51(8):1710-1719.