Fundamentals - Preventive Biomechanics - page 149

Fig. 3.36 Pressure-time threshold curves with regard to pressure ulcer development: a recent
shape proposal by (Linder-Ganz et al. 2006), b hyperbolic shaped curves established in

1959-1994 and c combined diagrams of (a) and (b)

3.5.2 Threshold Values for Animal Tissue

Kosiak, in 1959 and 1961, with focus on ischaemia, examined the effects of time-
pressure relationships in dog and rat experiments suggesting an inverse relation-
ship between the time of applied pressure and the pressure value causing tissue
damage (Kosiak 1959, 1961). Similarly, in 1974, Dinsdale from swine experiments
(Dinsdale 1974), in 1976, Reswick and Rogers from a human study (Reswick and
Rogers 1976), in 1981, Daniel from swine experiments (Daniel et al. 1981), and
Salcido from rat experiments (Saldico 1994) established pressure-time curves (see
Fig. 3.36 b). It was proposed in a recent study however, that such pressure-time
curves should be more sigmoid in shape rather than hyperbolic (see Fig. 3.36 a),
(Linder-Ganz and Gefen 2004).
Studies on limited interstitial fluid flow resulting in impaired metabolic cell
processes show that external pressure further unbalances regulation processes
(Reddy et al. 1981; Zhang et al. 1997). More recent works have concentrated on
the ischaemia-reperfusion injury phenomenon associated with local tissue
destruction after tissue unloading due to waste products in the tissue as a result of
preceding ischaemia, e.g. (Grisotto et al. 2000; Nanakawa and Mori 2005; Peirce
et al. 2000). In addition to ischaemia and ischaemia-reperfusion, damage induced
through cell (shear-) deformation has been investigated indicating that increase of
tissue damage and increase of applied shear strains are related (Bouten 2001;
Breuls et al. 2003; Stekelenburg et al. 2007; Ceelen et al. 2008). Implicitly con-
firming that finding, it was shown earlier that muscle tissue can bear high
hydrostatic pressures without showing signs of necrosis (Husain 1953). Muscle
stiffening was observed as a result of prolonged compressive loading by Gefen
et al. (2005) and Linder-Ganz and Gefen (2004). Formation of edema during and
after tissue loading could possibly explain this finding. As a result it was
hypnotized that muscle tissue is exposed to higher stress situation and pressure
sores are thus additionally promoted. Amongst experiments with animals, the latter
hypothesis was supported by use of computational models.