Distribution of interstitial fluid pressure and fluid volumes in hind‐limb skin of rats: relation to meridians?

To determine the distribution of interstitial fluid pressure (P_i) and volume (V_i), and to relate the distribution of these parameters to the distribution of potential meridians located by measurement of electrical impedance, we measured P_i, extracellular fluid (V_e) and plasma volumes (V_p) in 14 pre‐defined skin areas, 2 × 2 mm, and in concave and convex regions on the hind‐limb and groin of rats in control conditions. P_i was measured with sharpened glass capillaries connected to a servo‐controlled counter‐pressure system, while V_e and V_p were determined as the extravascular distribution spaces of ⁵¹Cr‐EDTA and ¹²⁵I‐human serum albumin, respectively. V_i was calculated as V_e – V_p, and V_w as the difference between skin wet and dry weight. Grand mean P_i averaged –0·81 mmHg (SD 0·83, n=95). P_i in skin was significantly higher in lateral and medial parts of the medial aspect of hind‐limb compared to pressures in the intermediate area (P<0·05). Pressures in the concave groin and the convex knee area were more negative and positive, respectively, than in the flat intermediate central hind‐limb area. There was a significantly higher V_i (P<0·05) and V_w (P<0·05) in the lateral side than that in the medial side. V_p was higher medially and laterally than in the intermediate area (P<0·05 for both comparisons), and correlated positively and significantly with P_i (r=0·66, P<0·05). No correlation was found between P_i and electrical impedance. The study suggests that the distribution of P_i, V_i, V_p and V_w is heterogeneous in hind‐limb skin at a macroscopic level without obvious relations to potential meridians.