RESUMEN
Ischemia reperfusion injury (IRI) involvement in pressure ulcers (PU) progression via a surge of oxidative stress and inflammatory responses is well documented. IRI strongly depends on the mechanical loading history. We present a generalized IRI model considering external loading, dynamic tissue healing capacity, accumulating mechanical and reperfusion-mediated damages and competing repair processes of saturating nature. Reperfusion depends on strain and strain rate to enhance loading history sensitivity. Tissue-specific ulceration susceptibility is assumed dependent on variable accumulated damage. We study damage evolution under cyclic loading having several strain expulsion profiles and demonstrate load relief history has critical impact on PU progression. Abrupt load removal generally follows existing models representing extreme repair/damage. We show (first time in silico) that under certain conditions (previously experimentally identified), IRI becomes repairing rather than damaging. In particular, we recapitulate the preconditioning and postconditioning IRI hallmarks. Finally, it is customary among physicians and nurses to promptly alleviate mechanical load applied to patients lying in bed for extended periods and in risk of developing PUs. We demonstrate this practice can be harmful. If load removal is performed early while reperfusion is still beneficial, then this conduct is suitable. However, if critical tissue damage has been crossed, then abrupt expulsion can constitute the worst-case scenario for patient outcome. If no preliminary patient documentation is available, we recommend gradual load removal since risks of accelerated damage eventually leading to ulceration supersede the improved repair potential benefit.