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 t hat the lymphatic network in leg skin might be adapted to cope with a great er fluid load. The dermal lymphatics of the forearm and lower leg were stud ied in white-skinned and brown-skinned men using fluorescence video microsc opy. From video print lymphangiograms the following were determined: lympha tic length density at a series of radii from the centre of the lymphangiogr am (LDr); maximum lymphatic density (LDmax); total length of lymphatic vess el (LL); maximum spread of lymphatic vessel; number and size of lymphatic r ings (continuous circuits of vessel); and vessel diameter. There were no di fferences between the two racial types, but clear differences between the a rm and leg. In the leg, mean (+/- SD) peak LDr (25.13 +/- 5.65 cm(-1)), LDm ax (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 respectiv ely, P less than or equal to 0.001). In the region of maximum lymphatic den sity 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 mu m (leg) and 94. 8 +/- 10.9 mu m (arm). Leg skin thus has a denser and more extensive lympha tic network than arm skin. This supports the hypothesis that lymph transpor t capacity in the leg is enhanced to compensate for a greater gravitational fluid loading. (C) 1999 Academic Press.