The local pathology of interstitial edema: surface tension increases hydration potential in heat-damaged skin

The local pathogenesis of interstitial edema in burns is incompletely understood. This ex vivo study investigates the forces mediating water-transfer in and out of heat-denatured interstitial matrix. Experimentally, full-thickness dermal samples are heated progressively to disrupt glycosaminoglycans, kill cells, and denature collagen under conditions that prevent water loss/gain; subsequently, a battery of complementary techniques including among others, high-resolution magnetic resonance imaging, equilibrium vapor pressure and osmotic stress are used to compare water-potential parameters of nonheated and heated dermis. The hydration potential (HP) determined by osmotic stress is a measure of the total water-potential defined empirically as the pressure at which no net water influx/efflux into/from the dermis is detected. Results show that after heat denaturation, the HP, the intensity of T2-weighed magnetic resonance images, and the vapor pressure increase indicating higher water activity and necessarily, smaller contributions from colloidosmotic forces to fluid influx in burned relative to healthy dermis. Concomitant increases in HP and in water activity implicate local changes in interfacial and metabolic energy as the source of excess fluid-transfer potential. These ex vivo findings also show that these additional forces contributing to abnormal fluid-transfer in burned skin develop independently of inflammatory and systemic hydrodynamic responses.