The Passage of Fluid and Protein through the Human Capillary Wall during Venous Congestion.

It has been demonstrated in normal human subjects by several methods that during venous congestion fluid is filtered from the blood into the tissue spaces. This passage of fluid through the capillary wall has been identified by comparing blood samples removed during normal circulation and during venous congestion (Schultz and Wagner (1909); Rowe (1915); Dautrebande, Davies and Meakins (1923); Peters, Eisenman and Bulger (1925)). It has been observed also that when the venous pressure in the legs is increased by quiet standing, fluid is filtered from the blood stream with a consequent reduction in circulating blood volume (Thompson, Thompson and Dailey (1928); Waterfield (1931)). The filtration produced by measured grades of venous congestion has been measured also by plethysmographic methods in which the accumulation of fluid in the tissue spaces was estimated by measuring the increase in limb volume (Drury and Jones (1927); Krogh, Landis and Turner (1932)). The capillary wall has usually been regarded as relatively impermeable to proteins (Krogh (1929); Thompson, Thompson and Dailey (1928); Krogh, Landis and Turner (1932)). Waterfield (1931) however, differed from Thompson, Thompson and Dailey in finding that during standing the blood lost not only fluid but also a significant amount of protein. Drinker and his co-workers (1931) have called attention to the high concentration of protein often found in lymph. Maintaining that tissue fluid and lymph are identical, they regard the capillary wall as everywhere quite permeable to protein even under normal conditions. A retrograde movement of protein from the tissue spaces through the capillary wall into the blood during venous stasis has been described by Plass and Rourke (1927). They found that during venous congestion the blood proteins were always increased by a greater percentage than was cell volume. This was believed to indicate that during venous congestion proteins must pass from the tissue spaces into the blood stream. It will be shown below that the direct comparison of percentage increase in cell volume with the percentage increase in plasma proteins is unjusti-