THE EFFECTS OF TEMPERATURE AND OF TISSUE PRESSURE ON THE MOVEMENT OF FLUID THROUGH THE HUMAN CAPILLARY WALL

Abstract

A pressure plethysmograph was arranged so that each determination of "reduced arm volume" (i. e., tissue volume with the blood vessels collapsed) required only 2 minutes'' stoppage of blood flow. The apparatus could be kept at a temp. constant within 1[degree] C. Measurements of "reduced arm volume" were relatively independent of the variations in arm volume produced by vasomotor changes or by simple engorgement of the veins. During 2-min. periods of 200 mm. Hg pressure the plethysmograph expressed only negligible quantities of fluid from the segment of forearm enclosed within it. The movement of fluid through the human capillary wall was studied in relation to venous pressure, temp. and duration of venous congestion. Above an average venous pressure of 12 cm. water the rate of filtration was directly proportional to the increase in venous pressure. A unit rise in venous pressure (1 cm. water) increased the filtration rate by 0. 0028 cc. per min. per 100 cc. of forearm when the congestion periods were 30 minutes long and by 0. 0033 cc. per min. per 100 cc. of forearm when the congestion periods were 10 min. long. The temp. of the forearm exerted a conspicuous effect on the rates of filtration produced by given venous pressures. In general, the rates of filtration produced by venous pressures of 30, 40, 50 and 60 cm. water with a forearm temp. of 44 to 45[degree] C. were almost twice as great as those produced by the same pressures with a temp. of 14 to 15[degree] C. The rate of filtration produced by any given venous pressure decreased rapidly as fluid accumulated in the tissue spaces. The filtration rate was reduced most rapidly during the first 30 min. of venous conges- tion. When sufficient fluid had accumulated in the tissue spaces, low venous pressures failed to produce further filtration. With large accumulations of fluid in the tissue spaces the filtration rate was decreased by an amount which was equivalent to a tissue pressure as high as 35 cm. water. The importance of temp. and tissue pressure, is briefly discussed with reference to normal fluid balance and to the formation of edema.