Simultaneous measurement of interstitial fluid pressure and load in rat skin after strain application in vitro

Skin provides the flexible, protective covering of the body. It consists of a network of fibrous proteins embedded in a viscoelastic gel. Theoretical models of soft tissue demonstrate that behavior of such systems is strongly influenced by the relationship between the interstitial fluid pressure (P(if)) and solid matrix stress. A microtensiometer for loading skin uniaxially in vitro was, therefore, developed and used in conjunction with the established servo-null micropipette technique to measure P(if). Dorsal rat skin specimens were preloaded to 100 mN, where P(if) was 2.3 +/- 1.3 mmHg (mean +/- SE, n = 12) above ambient, and then strained by 4%. Load instantaneously increased and the subsequent decay was described by the function, F(t) = F(1)[1-C(f)Ln(t)]. F(1), related to the instantaneous elasticity, was 272 +/- 42 mN (n = 12) while, C(f) was 0.0894 +/- 0.0026 [Ln(s)](-1) (n = 12). A similar function P(t) = P(s)(1) x [1-C(ps)Ln(t)], where P(s)(1) = 27 +/- 5 mmHg and C(ps) = 0.1274 +/- 0.0097 [Ln(s)](-1) (n = 12) fitted the decay of P(if) after 20 s with a residual > or = 0.82, though, P(if) fell more rapidly over the initial 10 s. P(if) and stress can be measured simultaneously with the apparatus, though more precise determination of the depth at which pressure is measured is required for quantitative comparison of the magnitude of these two parameters.