Increased dermal lymphatic density in the human leg compared with the forearm.

During orthostasis, capillary filtration pressure is higher in the leg than in the arm due to the effect of gravity. We investigated the possibility that the lymphatic network in leg skin might be adapted to cope with a greater fluid load. The dermal lymphatics of the forearm and lower leg were studied in white-skinned and brown-skinned men using fluorescence video microscopy. From video print lymphangiograms the following were determined: lymphatic length density at a series of radii from the centre of the lymphangiogram (LDr); maximum lymphatic density (LDmax); total length of lymphatic vessel (LL); maximum spread of lymphatic vessel; number and size of lymphatic rings (continuous circuits of vessel); and vessel diameter. There were no differences between the two racial types, but clear differences between the arm and leg. In the leg, mean (+/- SD) peak LDr (25.13 +/- 5.65 cm-1), LDmax (32.95 +/- 6.89 cm-1), LL (40.17 +/- 27.42 cm), and spread (1.39 +/- 0.08 cm) were all significantly higher than in the arm (18.03 +/- 5.48 cm-1, 23.91 +/- 7.21 cm-1, 11.76 +/- 5.47 cm, and 1.00 +/- 0.05 cm respectively, P </= 0.001). In the region of maximum lymphatic density there were 2.4 times more rings in the leg than in the arm, ring size being similar. Vessel image diameters were 89.6 +/- 26.3 micron (leg) and 94.8 +/- 10.9 micron (arm). Leg skin thus has a denser and more extensive lymphatic network than arm skin. This supports the hypothesis that lymph transport capacity in the leg is enhanced to compensate for a greater gravitational fluid loading. Copyright 1999 Academic Press.