Introduction: This study evaluated the repeatability of a heating and pressure protocol using laser Doppler flowmetry to measure the full dynamic range of skin microvascular responses at the sacrum and heel - key sites for pressure injury risk. Methods: Twelve healthy participants (10 male, 2 female; mean age 28 ± 4 years; stature 1.77 ± 0.11 m; body mass 72.6 ± 11.9 kg; body mass index 23 ± 3 kg/m²) completed sacrum assessments. Eleven participants (9 male, 2 female; mean age 28 ± 4 years; stature 1.77 ± 0.57 m; body mass 79.5 ± 9.8 kg; body mass index 20.4 ± 4.5 kg/m²) completed heel assessments. Each participant underwent three identical experimental sessions comprising four phases: baseline, local heating, loading, and pressure release. Skin blood flow was measured continuously. Repeatability was assessed using intraclass correlation coefficients (ICC), with an ICC of 0.75 as a minimum threshold for acceptable repeatability. Four methods were tested to identify the pressure at which blood flow ceased: segmental regression, visual analysis of the initial plateau in blood flow, visual analysis of the final cessation of blood flow, and the plateau that corresponds the final-minute mean. Results: The protocol showed good to excellent repeatability for baseline flow, settled flow at 42°C, and post direct-pressure reactive hyperaemia. Maximum combined thermal and reactive hyperaemia demonstrated excellent repeatability at the sacrum (ICC = 0.93) and heel (ICC = 0.91), while the area under the curve showed good repeatability at the sacrum (ICC = 0.81) and excellent at the heel (ICC = 0.90). Segmental regression showed the strongest repeatability (ICC = 0.90 at the sacrum; ICC = 0.84 at the heel). Visual inspection of the initial plateau in blood flow and absolute cessation of blood flow also exceeded the threshold for acceptable repeatability. Conclusion: This study presents a reproducible protocol for assessing pressure-induced microvascular compromise, capturing responses from complete vascular occlusion to peak thermal-pressure hyperaemic vasodilation. Applied at the sacrum and heel, it offers a quantifiable, non-invasive tool to investigate pressure injury risk in vulnerable populations. It also supports future evaluations of support surfaces, offloading strategies, and novel therapeutic interventions to improve tissue pressure tolerance.
Lloyd et al. (Thu,) studied this question.