Using Reactive Hyperemia to Assess the Efficacy of Local Cooling on Reducing Sacral Skin Ischemia Under Surface Pressure in People With Spinal Cord Injury: A Preliminary Report

Objectives: To investigate the efficacy of local cooling on reducing sacral skin ischemia in a weight-bearing position, and to identify the underlying physiological mechanisms using wavelet-based spectrum analysis of reactive hyperemia in people with spinal cord injury (SCI). Design: Repeated-measures and before-after trial design. Setting: University research laboratory. Participants: Wheelchair users with SCI with injury level between C4 and T5 (n=10) and able-bodied controls (n=10). Interventions: Three protocols consisting of pressure without temperature changes, pressure with local cooling (Δt=-10 C), and pressure with local heating (Δt=+10 C) were tested. Each protocol consisted of a 10-minute baseline period, a 20-minute loading period at 60mmHg, and a 20-minute recovery period (reactive hyperemia). A 30-minute washout period was allowed between protocols. Main Outcome Measures: A compound sensor head consisting of laser Doppler and heating and cooling probes was used to measure sacral skin blood flow and control skin temperature. Reactive hyperemic response to pressure and temperature stimuli was characterized in the time and frequency (metabolic [.0095-.02Hz], neurogenic [.02-.05Hz], and myogenic [.05-.15Hz] components) domains. Results: Pressure with local cooling resulted in a smaller reactive hyperemic response in both people with SCI and able-bodied controls as compared with pressure with local heating (P<.017) and pressure without temperature changes (P<.017), and the smaller hyperemia was attributed to reduced metabolic and neurogenic activities. People with SCI showed an attenuated response in reactive hyperemia (P<.017). Conclusions: This study supports the concept of using local cooling to reduce skin ischemia under surface pressure in people with SCI.