Influence of temperature on vascular density at the sacrum and heel

Abstract

Introduction: localised damage to the skin through a combination of sustained pressure and repeated shearing forces can lead to the development of pressure ulcers (PUs). In the UK, the cost of treating PUs and other hard-to-heal (chronic) wounds is ~£8 billion annually.1 Animal studies have identified the use of localised cooling to influence the skin's tolerance to mechanical loading by reducing the tissue's metabolic demands.2 However, the mechanisms by which cooling may enhance skin tolerance to loading and shearing forces remain poorly understood. Furthermore, the efficacy of cooling may differ across populations and anatomical sites. The aim of this study was to examine how different levels of localised cooling influence microvascular properties in younger and older adults.

Method: younger and older adults with no health conditions underwent an in vivo characterisation of vascular density (expressed as a percentage of tissue comprising blood vessels against the depth of detection) at two skin sites: the sacrum and posterior heel. For the evaluation, three different local temperatures were used: 38°C, 24°C and 16°C. Vascular density was assessed using a dynamic optical coherence tomography scanner. The sacrum underwent a protocol to cause pressure-induced ischaemia and post-occlusive hyperaemia.3 The heel underwent a standardised repeated shearing protocol.4 Peak vascular density data were analysed using a two-way analysis of variance to assess the interaction between temperature condition and anatomical site.

Results: in this study, 22 younger (mean age: 25±4 years; mean weight: 71±9kg; mean height: 176±9cm) and 19 older adults (mean age: 65±4 years; mean weight: 70±14kg; mean height: 171±10cm) were included. There was a main effect of temperature (p<0.001) on peak vascular density and an interaction effect with skin site, where vascular density was greater in the sacrum compared to the heel at all temperatures (p<0.001). Post hoc analysis revealed 24°C (8.9±3.5%) at the sacrum was lower in terms of peak vascular density than both 16°C (11.7±4.1%; mean difference: 2.3%; 95% confidence interval (CI): –3.6, 1.0; p<0.001) and 38°C (11.1±5.4%; mean difference: 2.9%; 95% CI: –5.1, 0.6; p=0.008). At the heel, vascular density at 16°C (3.2±2.3%) was lower than 24°C (5.0±4.1%; mean difference: 1.8%; 95% CI: –3.1, 0.5); p=0.005) and 38°C (7.9±8.7%; mean difference: 4.7%; 95% CI: –7.1, 2.4; p=0.005). Depth at peak vascular density was 0.4mm at the sacrum and 0.6mm at the heel.

Conclusion: findings demonstrated there was an effect of temperature on vascular density, which was dependent on skin site. These data also highlight differences in the depth of the vascular density profiles, with more superficial microvasculature observed at the sacrum. These results indicate there were distinct microvascular responses to sustained pressure and shearing forces at two skin sites at risk of PU development, which could be used to inform the efficacy of skin cooling in maintaining skin tissue viability.

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Identifiers

ORCID for Ralph J.F.H. Gordon: orcid.org/0000-0002-8441-9292

ORCID for Charlotte E. Stevens: orcid.org/0009-0009-7612-6228

ORCID for Davide Filingeri: orcid.org/0000-0001-5652-395X

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