Recovery of vasomotor response in human spinal cord transection

Vasomotor responses of the skin of the thumb and the big toe were measured in normal subjects and patients with spinal transection at a neutral ambient temperature of 22.0 +/- 0.5 degrees C, and in a cool (12.0 +/- 0.5 degrees C) and warm (32.0 +/- 0.5 degrees C) environment. The vasomotor response of the hand and foot to the cooling and warming of part of the opposite upper or lower extremity was also recorded. Spinal transection at T5-11 abolishes acutely all vasomotor responses in the paraplegic lower extremities, but does not alter the responses in the upper extremities. By 4 months, the vasomotor tone in the lower extremities at a neutral ambient temperature returned to normal values as did the response to a cool and warm environment. The crossed vasomotor reflex to cooling and warming one lower extremity recovers more slowly, requiring a period of 18 months for complete recovery. The slower recovery of the vasomotor reflex in spinally transected man than in similarly treated dogs is though to be due to the greater spinal shock in the former. The recovery of vasomotor responses in the paraplegic limbs to cooling and warming after thoracic transections suggests that these responses are primitive and powerful thermoregulatory mechanisms.