Biomedical Engineering Reference
In-Depth Information
From the above described animal studies it shows that ischaemia is involved in
pressure ulcer pathogenesis, but cell deformation apparently plays a major role,
particular in the beginning of sore formation. Clearly, besides the extrinsic factor
of mechanical tissue loading there exist several other intrinsic factors that increase
the risk to develop pressure sores: e.g. gender, age, skin condition, weight, mental
disability, malnourishment, moisture and incontinence.
3.5.3 Work Hypothesis
Concluding, it can be assumed that pressure sores (at the human body) develop as
a result of exceedance of mechanical tissue ''stress thresholds'' over a prolonged
period of time inside the tissue and are initiated not only from compressive stress
but rather from shear and possibly tensile stress and their coexistence, respectively.
Since to date no reliable biomechanical restrictions, i.e. mechanical limits,
exist, the authors thus assume that (at least with respect to the development of anti-
decubitus systems) a technical body support system is appropriate regarding
pressure sore prevention if (internal) tissue stresses, especially at the bone surface,
are low. The approach presented in
Chap. 6
offers the possibility to objectively
determine such mechanical tissue loadings.
This hypothesis can be readily applied to the area of comfort: The effects of
(extra-corporal) body supporting systems on the human body generally cause
reactions in deeper (soft) tissue regions, especially inside the muscle tissue. This
inevitably and automatically causes disorders in terms of anxiety and muscle
tensions (in seated or recumbent posture) which lead agitation and restlessness and
pain.
Insomnia
and
compensating
body
movements
are
the
consequences
(''physiological-mechanical chain'').
Due to lack of knowledge but to at least provide a intuitive classification of the
simulated internal (human) tissue stress caused by the support systems presented in
literature as depicted in Fig.
3.36
.
