The effects of local cooling rates on perfusion of sacral skin under externally applied pressure in people with spinal cord injury: an exploratory study

Study design: Experimental before–after design. Objectives: The objectives of this study were to explore the effects of local cooling rates on perfusion of sacral skin under externally applied pressure in people with spinal cord injury (SCI). Setting: Research laboratory. Methods: Seventeen participants, including seven wheelchair users with SCI and ten able-bodied (AB) controls. Each participant underwent seven protocols, including pressure (60 mmHg) with local cooling (∆t = −10 °C) for 20 min at three cooling rates (−0.5, −4, −10 °C/min), pressure with local cooling for 40 min, pressure with local heating (∆t = +10 °C), local cooling without pressure, and pressure without temperature changes. Each protocol included a 10-min baseline, a 20-min (or 40-min) loading period and a 20-min recovery. A compound sensor head consisting of laser Doppler and heating and cooling probes was used to measure sacral skin blood flow and temperature in the prone position. Blood flow responses were characterized by peak blood flow, recovery time, and total blood flow in the recovery period. Results: The results demonstrated that the cooling rate at −10 °C/min resulted in smaller skin blood flow response compared with −0.5 °C/min (p < 0.05) but were not significantly different to the cooling rate at −4 °C/min. There was a significant difference in the recovery time between the 20-min cooling compared with the 40-min cooling for the SCI group (p < 0.05). Conclusions: Our findings provide initial evidence that local cooling rates affect skin blood flow responses under externally applied pressure in people with SCI.