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Section I. Measurement of exchange in the microcirculation
MICROVASCULAR
RESEARCH
Section
5,234 (1973)
I. Measurement of Exchange Microcirculation
in the
Introduction PAUL C. JOHNSON
The microcirculation is often referred to as the “business end” of the circulatory systemin recognition of the fact that this is the area in which the exchangetransactions between blood and tissue occur. The development of techniques for quantitating the exchange process at the microcirculatory level has proved quite difficult, however. As a consequence,most of what we know about exchange is based on input-output analysis of diffusible materials in the blood perfusing organs or regions of the body, changesin organ weight or volume reflecting net capillary filtration or absorption, and rate of appearanceof large molecules in lymph. With the rapid development of quantitative techniques for studying the microcirculation in the past ten years, the problem of studying exchangeat the microcirculatory level has again attracted interest. Current concepts of microcirculatory function commonly localize the exchange process to the capillary alone. However there is evidence, some of it not new, which implicates the venule as well, especially in exchange of large molecules. Recent studies of tissuePO2 indicate that at least someoxygen may leak out of the arteriole before the blood reachesthe capillary network. The specific locus of the exchangeprocesstherefore is not entirely resolved. Further studies at the microcirculatory level are necessary to define the relative importance of the different microvascular units in the exchange process. The development of quantitative methods for studying exchange may also lead to examination of the movement of molecules of interest within the interstitial space. This is an area which has largely been beyond the scopeof our technology to this time. However the existenceof concentration gradients within the tissue is now being recognized and the tissue is no longer regarded necessarilyas an infinite sink or a well-mixed compartment for tracer molecules. The difficulties implicit in exchange studies at the microcirculatory level can be appreciated from examining the reports in this section. At the sametime, the benefits to be derived are also evident. Obviously nature does not give up her secretseasily. On this basis it can be surmised that the process of microcirculatory exchange are among the most treasured secretsof all.
Copyright All rights
0 1973 by Academic Press, Inc. of reproduction in any form reserved.
234
RESEARCH
Section
5,234 (1973)
I. Measurement of Exchange Microcirculation
in the
Introduction PAUL C. JOHNSON
The microcirculation is often referred to as the “business end” of the circulatory systemin recognition of the fact that this is the area in which the exchangetransactions between blood and tissue occur. The development of techniques for quantitating the exchange process at the microcirculatory level has proved quite difficult, however. As a consequence,most of what we know about exchange is based on input-output analysis of diffusible materials in the blood perfusing organs or regions of the body, changesin organ weight or volume reflecting net capillary filtration or absorption, and rate of appearanceof large molecules in lymph. With the rapid development of quantitative techniques for studying the microcirculation in the past ten years, the problem of studying exchangeat the microcirculatory level has again attracted interest. Current concepts of microcirculatory function commonly localize the exchange process to the capillary alone. However there is evidence, some of it not new, which implicates the venule as well, especially in exchange of large molecules. Recent studies of tissuePO2 indicate that at least someoxygen may leak out of the arteriole before the blood reachesthe capillary network. The specific locus of the exchangeprocesstherefore is not entirely resolved. Further studies at the microcirculatory level are necessary to define the relative importance of the different microvascular units in the exchange process. The development of quantitative methods for studying exchange may also lead to examination of the movement of molecules of interest within the interstitial space. This is an area which has largely been beyond the scopeof our technology to this time. However the existenceof concentration gradients within the tissue is now being recognized and the tissue is no longer regarded necessarilyas an infinite sink or a well-mixed compartment for tracer molecules. The difficulties implicit in exchange studies at the microcirculatory level can be appreciated from examining the reports in this section. At the sametime, the benefits to be derived are also evident. Obviously nature does not give up her secretseasily. On this basis it can be surmised that the process of microcirculatory exchange are among the most treasured secretsof all.
Copyright All rights
0 1973 by Academic Press, Inc. of reproduction in any form reserved.
234