Physical forces in blister formation. The role of colloid osmotic pressure and of total osmolality in fluid migration into the rising blister.

The physical forces operative in the fluid migration from the interstitial spaces into the blister cleft have not been directly measured until now. The colloid osmotic pressure and the total osmolality were determined in suction blister fluid after mild suction blister production by a modified "Dermovac" and in blister fluid of patients with dermatitis herpetiformis, bullous allergic contact dermatitis and pemphigus vulgaris and in the sera of healthy persons. The colloid osmotic pressure was measured by means of a recently developed osmometer with a semipermeable membrane between 2 chambers, one of them filled with Ringer solution, the other with the blister fluid or serum sample. The negative pressure in the first chamber was determined. The colloid osmotic pressure of suction blister fluid averages approximately 7 cm H2O, the values reach about 20 cm H2O in bullous diseases and about 38 cm H2O in the normal sera. The blister fluid colloid osmotic pressure has to rise to about 15 cm H2O or more to cause the fluid transport from the interstitial spaces of the surrounding tissue into the blister because of the negative interstitial fluid pressure and the colloid osmotic pressure of the interstitial fluid. Otherwise the blister fluid is reabsorbed back into the interstitial spaces. The total osmolality does not differ in the serum and in the blister fluid. It does not seem to be etiologically connected with the fluid transport into the rising blister.