PRESSURE-VOLUME RELATIONSHIP FOR RAT DERMIS - COMPRESSION STUDIES

The relationship between tissue hydrostatic pressure and fluid content is an important determinant of the response of the microvascular exch ange system to perturbations. However, only a limited number of studie s relating these parameters have been reported. To add to this body of information, fully swollen rat dermis in vitro was subjected to succe ssive compressive loads in an apparatus in which tissue thickness chan ges were monitored. At steady-state the mechanical load on the tissue was balanced by the interstitial fluid pressure within the tissue whil e the fluid content of the tissue was determined from the unstressed t issue fluid content and changes in tissue thickness. The range of cond itions investigated was from moderate overhydration through normal tis sue fluid content to significant dehydration. From the relationship be tween interstitial fluid pressure and tissue fluid content (expressed as mass of fluid per mass of fat-free dry tissue) the tissue complianc e was determined. Compliance, defined as the rate of change of the tis sue fluid content with changes in interstitial pressure, increased wit h tissue hydration. The compliance determined using compressive loads and steady-state response of tissue thickness compares favourably with the limited amount of information available about this tissue propert y which is critical in the determination of tissue fluid balance. Comp liance ranged over one order of magnitude for the conditions studied a nd at normal hydration, tissue fluid volume changed by about 6.6% per mmHg in tissue hydrostatic pressure.