RENAL LYMPHATIC FUNCTION FOLLOWING VENOUS-PRESSURE ELEVATION

The renal lymphatic system plays an important role in removing excess fluid from the kidneys. Unfortunately, the factors influencing lymphat ic flow are difficult to measure. We used a simple model to represent renal lymphatics as a single pressure source (P-L pushing lymph throug h a single resistance (R(L)). In anesthetized dogs, we cannulated rena l lymphatics and measured lymph flow rate (Q(L)) as we varied pressure (P-O) at the outflow end of the lymphatics. There was no significant change in Q(L) as we increased P-O from -5 to 0 cm H2O. In other words , there was a plateau in the Q(L) vs. Po relationship. At higher P-O's , Q(L) decreased linearly with increases in P-O. From this linear rela tionship, we calculated R(L) as -Delta P-O/Delta Q(L) and we took P-L as the P-O at which Q(L) = 0 mu l/min. At baseline, R(L) = 0.34 +/- 0. 14 (SD) cm H2O . min/mu l and P-L = 8.2 +/- 4.4 cm H2O. When we increa sed renal venous pressure (P-V) from baseline (3.5 +/- 3.0 cm H2O), th e plateau in the Q(L), vs. P-O relationship extended to higher P-O's, R(L) decreased, and P-L increased. Renal interstitial fluid volume and interstitial pressure increased following elevation of P-V The extens ion of the Q(L) vs. P-O plateau with increasing P-V suggests that rena l interstitial pressure may partially collapse intrarenal collecting l ymphatics which may compromise lymph flow.