Sweating and cutaneous vasodilation responses above the lesion during passive heat stress in persons with thoracic spinal cord injuries

Background Sweating and cutaneous vasodilation responses in humans increase with an increase in body core and skin surface temperatures; a ratio of contributions is 10 to 1, respectively, via an excitation of sympathetic nervous system. However, these responses are absent or blunted on the skin below the lesion in persons with a spinal cord injury. The diminished thermoregulatory capacity may contribute to a decline in performance of a competition. In case of able‐body (AB) marathon, the optimum ambient temperature (T opt ) to exert a competitiveness would be around 10°C and a race time tends to be worth once the temperature was over T opt . In our analysis from the past 20 years of the Oita International Wheelchair Marathon, a completion rate was ~8% in marathon and half‐marathon under ambient temperature (T a ) 18.3°C (13.3–26.3, min‐max) and relative humidity 63% (28–96). The rate tended to decrease the more with the more increased and decreased T a on the both sides of 22°C. Thus, competitiveness in wheelchair athletes would be influenced from climate condition beyond developing wheelchair and T opt may not be the same as AB. Diminished thermoregulatory capacity in persons with a spinal cord injury relates their competitiveness and varies T opt . However, information for their thermoregulation is still necessary. Objectives Sweat rate (SR) and cutaneous vasodilation responses to a thermal stress are absent in persons with a cervical spinal cord injury (CSCI) and are not observed distal to the lesion in persons with lower spinal cord injuries. It remains unknown whether the thermo‐effector responses above the lesion in spinal cord injuries are similar to AB, and related to the time since the injury. Methods Seven persons with a thoracic spinal cord injury (TSCI; Th4‐10; time since injury 1–24 yrs) and 10 AB subjects participated in this protocol. While in the supine position, 33‐°C water was circulated through a water‐perfused suit worn by each subject. After 30‐min rest, 10 min of baseline data were obtained. Then, 36‐ and 50‐°C waters were perfused through the upper and lower parts of the suit, respectively, until esophageal temperature increased by 1°C. Results The heat stress increased cutaneous vasodilation and SR on the chest (C4; sensate skin for SCI) in both groups. However, the increase in these variables was suppressed in LSCI. Moreover, the magnitude of the increase in chest SR at the end of heating was positively related to the time since the injury in LSCI (r=0.98; P<0.0001). Conclusion Sweating and cutaneous vasodilation responses at 1‐°C increase in esophageal temperature above the lesion are suppressed in LSCI and sweating responses is possibly affected by time since the injury. The impaired thermoregulatory responses may be associated with the completion rate in a wheelchair marathon. Support or Funding Information This study was funded by the Research Foundation of NachiKatsuura City, the Nakatomi Foundation, and National Heart, Lung, Blood Institute Grant HL‐61388.