Submitted on September 16, 2008
Revised on March 19, 2009
Accepted on March 19, 2009
Swelling and pressure-volume relationships in the dermis measured by osmotic-stress technique
Maria Peran McGee1*, Michael Morykwas2, Nicole Levi-Polyachenko2, and Louis Argenta3
1 Wake-Forest University Medical School
2 Wake Forest Medical School
3 Wake Forest University Medical school
* To whom correspondence should be addressed. E-mail: mmcgee{at}wfubmc.edu.
Water transfer across the extracellular matrix (ECM) involves interstitial osmotic forces in as yet unclear ways. In particular, the traditional values of Starling forces cannot adequately explain fluid transfer-rates. Here, we reassess these forces by analyzing fluid-transfer in live pig and human dermal-explants. Pressure-potentials were controlled with inert polymers adjusted by membrane osmometry (range = 3-219 mm Hg), and fluid-transfer in/out of the explants was followed by sequential precision weighing. Water activity in the dermis was examined by NMR. In pigs, mean HP (hydration pressure; the pressure at which volume did not change) was 107 (SE 22) and 47 (SE 12) mm Hg at 4 and 37 °C (P-value = 0.012, paired t-test, n = 7). The equation, Volume change = Vmax/[1+(time/T1/2)]d, where Vmax is maximal volume-change; T1/2, time at volume = 1/2 Vmax; and d, a rate parameter, was fitted to experimental progression-curves (r2 >0.9), yielding Vmax values linearly related to pressure, with mean slopes -3.5 (SE 0.28) and -2.6 (SE 0.21) µl/g/mmHg at 4 and 37° C. The glycolysis-inhibitor Iodoacetamide increased mean Vmax by 0.176 (SD 56) µl/g and HP by 68 (SD 22) mmHg. Results with human explants were similar. NMR spin-spin relaxation times (T2) varied within 200-400 µm distances in directions perpendicular to the epidermis, with slopes reaching 0.03 ms/µm. Results support a mechanism where fluid transport across the ECM is locally regulated at µm scales by cell and fiber-gel- dependent osmo-mechanical forces. The large HP helps to explain the fast interstitial in/out flow rates observed clinically.
