Observations on Human Microvascular Function in Health and Disease

Although historically scientific attention has centred on the function of the heart and larger blood vessels the cardiovascular system exists to subserve the function of the microcirculation, those smallest blood vessels conventionally defined as arterioles, capillaries, venules and terminal lymphatics. The major generic functions of the microcirculation are summarised in table 1, knowledge of the determinants of which have been limited by the lack of technology to study processes which at the same time are often inaccessible, exquisitely sensitive to pernibation and involve minute structures. Nevertheless, in the last two decades techniques have been developed to register microvascular pressure, flow and certain aspects of permeability at least in superficial tissues (table 2). Table 1 Major functions of the microcirculation

Transport and exchange of nutrients and waste products between blood and tissue fluid. Maintenance of tissue fluid economy. Involvement in tissue defence, growth and repair.

Table 2 Major techniques available for studying the human microcirculation

In vivo capillary microscopy (capillary morphology). Dynamic capillary microscopy (capillary flow estimation). Single point laser Doppler fluximetry. Laser perfusion imaging. Dynamic capillary pressure measurement. Terminal lymphatic pressure measurement. Fluorescence microscopy. Capillary filtration coefficient measurement.