Interstitial-Matrix’ Fluid-Fluxes In Vivo: Subatmospheric Pressure Reverses Hydration-Potential in Heat-Denatured Dermis

Abstract

Interstitial flows modulate (a) the interchange of nutrients and metabolites between blood and parenchyma; (b) paracrine and endocrine signals; and (c) fibroblast mechanical responses. Previously, we found that hydration potential (HP), a measure of the local forces that drive interstitial flows, increases in dermis heated ex vivo. Here, we measured HP in dermis heated in vivo to probe its effectinintact animals. Subatmospheric pressure, 125mmHg, was applied in vivo for 3 hours to heated (15 sec, 100°C) and control dermis obtained as by-products from unrelated studies as approved by the IRB. Differential scanning calorimetry was used to determine the extent of collagen unfolding, and 1H magnetic resonance imaging to determine apparent diffusivity and anisotropy. HP was measured by osmotic stress, 3-219 mmHg, and influx/efflux trajectories were followed for ∼20 h to near equilibrium. The extent of unfolded collagen in vivo and ex vivo was 33 ± 3 and 34 ± 2 % of controls, respectively; apparent diffusion coefficients increased (10.1 ± 2 and 11.3 ± 1.5 versus 6.3 ± 3.7 x10−4 mm2/s), while fractional anisotropy decreased (0.289 ± 0.15 and 0.174 ± 0.07 versus 0.689 ± 0.27). These results suggest similar structural changes in both type-specimens. Mean HP of in-vivo denatured dermis decreased relative to the control and ex-vivo denatured explants: −15.2 ± 12.6 versus 30.9 ± 4.8 and 98 ± 7.4 mmHg, respectively (P-value < 0.05). After subatmospheric pressure, mean HP (48.1 ± 4.6 mm Hg) in in-vivo denatured dermis returned to baseline, while diffusivity decreased, and anisotropy increased. Lower HP values indicate excess fluid accumulation, consistent with suction forces developing in vivo upon denaturation; emerging convection-enhanced interstitial flows could explain the local edema (HP decrease) and its reversal (HP increase) by externally applied subatmospheric pressure.