Repeated Pressure and Shear Stress at the Posterior Heel Following Localized Skin Cooling: Protocol for a Repeated Measures Cohort Study.

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 United Kingdom 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 being exposed to pressure and shear during lying postures. Localized cooling and interface materials that reduce shear may offer potentially therapeutic benefits in the development of pressure ulcers. Yet the physiological mechanisms underpinning the potential benefits of localized cooling are not fully understood.

Objective: This study protocol aims to investigate how localized 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 measures design. Three cohorts will be recruited: (1) young and healthy (n=35), (2) older and healthy (n=35), and (3) with spinal cord injury (n=35). Participants will complete 3 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 standardized 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 (via Sebutape), structural skin properties (via optical coherence tomography), skin conductance (in microsiemens) and ratings of thermal sensation, comfort, and acceptance (via 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 had been enrolled in the study. Data collection and analysis are ongoing, and published findings are expected to be available in early 2026.

Conclusions: 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.

International registered report identifier (irrid): DERR1-10.2196/73250.