Abstract
Pressure ulcers are one of the most common complications of a spinal cord injury (SCI). Prolonged unrelieved pressure is thought to be the primary causative factor resulting in tissue ischemia and eventually pressure ulcers. Previous studies suggested that local cooling reduces skin ischemia of the compressed soft tissues based on smaller hyperemic responses. However, the effect of local cooling on nonlinear properties of skin blood flow (SBF) during hyperemia is unknown. In this study, 10 wheelchair users with SCI and 10 able-bodied (AB) controls underwent three experimental protocols, each of which included a 10-min period as baseline, a 20-min intervention period, and a 20-min period for recovering SBF. SBF was measured using a laser Doppler flowmetry. During the intervention period, a pressure of 60 mmHg was applied to the sacral skin, while three skin temperature settings were tested, including no temperature change, a decrease by 10 °C, and an increase by 10 °C, respectively. A multiscale entropy (MSE) method was employed to quantify the degree of regularity of blood flow oscillations (BFO) associated with the SBF control mechanisms during baseline and reactive hyperemia. The results showed that under pressure with cooling, skin BFO both in people with SCI and AB controls were more regular at multiple time scales during hyperemia compared to baseline, whereas under pressure with no temperature change and particularly pressure with heating, BFO were more irregular during hyperemia compared to baseline. Moreover, the results of surrogate tests indicated that changes in the degree of regularity of BFO from baseline to hyperemia were only partially attributed to changes in relative amplitudes of endothelial, neurogenic, and myogenic components of BFO. These findings support the use of MSE to assess the efficacy of local cooling on reactive hyperemia and assess the degree of skin ischemia in people with SCI.
Highlights
Pressure ulcers are a common complications of a spinal cord injury (SCI) that can significantly impact patients’ overall quality of life and even be life-threatening [1]
Our results showed that local cooling resulted in a decrease in Ems of blood flow oscillations (BFO) from baseline to reactive hyperemia, which was opposite to that resulted from local heating (Figures 3 and 4)
Our results showed that multiscale entropy could reveal differences in the structural properties of BFO during reactive hyperemia under three conditions, which cannot be revealed by time- or frequency-domain parameters
Summary
Pressure ulcers are a common complications of a spinal cord injury (SCI) that can significantly impact patients’ overall quality of life and even be life-threatening [1]. Elevated skin temperature has been identified as a causative factor of pressure ulcers [4,5]. Previous animal studies [4,6] showed that local cooling can reduce tissue damage under surface pressure. Based on these promising results, human studies were conducted to demonstrated that local cooling may reduce skin ischemia under pressure [7,8]. Our previous study [7] demonstrated that pressure with cooling induced a smaller reactive hyperemic response compared to pressure with no temperature change and pressure with heating both in people with SCI and able-bodied (AB) controls. We further showed that the smaller hyperemic response was attributed to reduced endothelial and neurogenic blood flow controls
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