Fluid Exchange Across Single Capillaries

All major organisms must establish and maintain proper water balance between the blood and interstitium. In 1896, Ernest Starling (61) presented the first modern description of the major forces governing fluid exchange across capillaries. His ideas were later confirmed by Landis (26-28). Al­ though many details have since been added to our knowledge of transcapil­ lary fluid exchange, Starling's fundamental assertions and Landis' observations still represent the foundations of our present understanding. Most studies of transcapillary fl uid exchange have been done on either single capillaries or isolated whole organs. Single capillary studies date from the work of Landis, while modern whole-organ studies began with the classic experiments ofPappenheimer & Soto-Rivera (53). In the last decade, renewed interest in the study of single capillaries has produced many experi­ ments designed to examine the biophysical and structural nature of the exchange barrier and the interstitium. This review discusses fluid exchange across single capillaries, with only a few references to whole organ-studies. Comprehensive reviews ofthe general subject of transcapillary exchange are available (21, 25, 40,57). Crone & Christensen's recent review (6) is espe­ cially good. Brief treatments of specific aspects of fluid exchange are recom-