Gordon, Ralph, Stevens, Charlotte, Worsley, Pete and Filingeri, Davide (2025) Repeated pressure and shear stress at the posterior heel following localised skin cooling: protocol for a repeated measures cohort study. JMIR Research Protocols, 14, [e73250]. (doi:10.2196/73250).
Abstract
Background: pressure in combination with shear forces can deform soft tissues and lead to development of pressure ulcers. The prevalence rate of pressure ulcers in the UK remains unacceptably high and can occur across the human lifespan. The posterior heel represents a common anatomical site for pressure ulcers, due to soft tissues lying adjacent to bony prominences and exposed to pressure and shear during lying postures. Localised cooling and interface materials which reduce shear may offer potentially therapeutic benefits in the development of pressure ulcers. Yet, the physiological mechanisms underpinning the potential benefits of localised cooling are not fully understood.
Objectives : this study protocol aims to investigate how localised cooling influences the skin’s microvascular, inflammatory, structural, and perceptual tolerance to repeated shear loading at the heel.
Methods: the protocol will be tested on individuals of different age, sex, skin tone and comorbidities, using a repeated-measure design. Three cohorts will be recruited: i) young healthy (n=35); ii) older healthy (n=35); iii) spinal cord injured (n=35). Participants will complete three testing sessions using a custom-built shearing rig with integrated thermal plate, during which the posterior aspect of the heel will be exposed to a standardised mechanical stimulus to elicit repeated pressure and shear loading. The experimental condition of each session will be determined by the temperature of the thermal plate, which will be set to either 36 °C (no cooling), 24 °C (mild cooling), or 16 °C (strong cooling). Continuous measurements will include kinetic coefficient of friction (CoF) and skin blood flow (via Laser Doppler Flowmetry; 40 Hz). Pro- and anti-inflammatory biomarkers in skin sebum (Sebutape), structural skin properties (Optical Coherence Tomography), skin conductance (µs) and ratings of thermal sensation, comfort, and acceptance (Likert Scales) will also be assessed before and after the shear stress protocol.
Results: recruitment began in January 2024. As of February 2025, 43 participants have been enrolled on to the study. Data collection and analysis are ongoing, published findings are expected to be available in early 2026.
Discussion: this analysis will help identify mechanisms of skin damage following repeated shear stress at the heel, furthering our understanding of superficial pressure ulcers. It will also establish physiological and perceptual thresholds for the protective effects of cooling from shearing-induced damage at the heel.
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