Experimental and quantitative analysis of microcirculatory water exchange.

Quantitative and direct studies of microcirculatory fluid exchange phenomena provide evidence that fluid tissue balance in omentum and mesentery is achieved through lymphatic drainage. Fluid exchange in muscle appears to alternate between filtration and absorption from the capillaries in synchrony with arteriolar vasomotion. Detailed calculations show that, in the absence of hydraulic or osmotic pumping at the level of the terminal lymphatics, tissue pressures are of the order of +6 cm H2O for both visceral and muscle tissue. It is concluded that these microcirculatory beds represent two extreme types of mechanisms for achieving fluid balance, and that most other tissues, with the exception of liver and tumors, operate in between.