DOI: 10.1097/01.ASW.0000305403.89737.6c
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PMID: 18156827
Issn Print: 1527-7941
Publication Date: 2008/01/01
Bioengineering Models of Deep Tissue Injury
Excerpt
For patients permanently confined to a wheelchair or a bed, pressure ulcers are a major health risk. Pressure ulcers typically appear in soft tissues enveloping bony prominences (eg, the ischial tuberosities), which are compressed by body weight against the supporting surfaces. In patients with central nervous system disorders, the combination of immobility, which imposes unrelieved tissue compression and shear stresses, and the lack or dysfunction of a pain "alarm" sensation creates the conditions for local prolonged tissue ischemia. Excessive prolonged tissue deformation from the bone's compression also causes cell death, leading to a pressure ulcer.1 However, ischemia is traditionally considered the primary factor in pressure ulcer etiology.2 Muscle tissue, the most vascularized tissue layer between the bone and skin during sitting and the tissue with the highest metabolic demand, is reported to have the lowest tolerance to mechanical compression.3 Accordingly, in the recent years, it was recognized that pressure ulcers can develop in muscles that pad bony prominences without any external indication of deep tissue necrosis during the early stages of injury.1,4-6 Therefore, the 2005 Consensus Meeting of the US National Pressure Ulcer Advisory Panel (NPUAP) introduced a new term, deep tissue injury (DTI), to classify this potentially life-threatening form of pressure ulcer, which is characterized by necrotic muscle tissue under intact skin. The current NPUAP's definition of a "suspected DTI" is "Purple or maroon localized area of discolored intact skin or blood-filled blister due to damage of underlying soft tissue from pressure and/or shear. The area may be preceded by tissue that is painful, firm, mushy, boggy, warmer, or cooler as compared to adjacent tissue (http://www.npuap.org).
Pressure ulcers and DTI do not develop spontaneously in animals, making basic research and applied research work more difficult. Special models need to be developed and verified to study the etiology of DTI and to design preventive or protective measures. The purpose of this review is to describe the frontier of biomedical research on DTI, with an emphasis on up-to-date computer modeling, imaging strategies, and cellular and tissue engineering methods. These new research tools allow well-defined, carefully controlled studies of tissue viability under prolonged loading, which was impossible until a few years ago. The discoveries made using these methods are expected to boost the understanding of DTI and lead to the development of improved medical protocols and preventive equipment for susceptible patients. Although the pathomechanics of DTI is discussed here from a bioengineering perspective, the physiologic mechanisms of injury and the clinical relevance are comprehensively addressed. For readers with a nonengineering background, a Glossary of Engineering Terms is provided.
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