Microcirculation During Low Flow States

Microcirculation represents the ultimate determinant of the outcomes of circulatory shock states. Microcirculatory function is the prerequisite for adequate tissue oxygenation and therefore organ function. It transports oxygen and nutrients to tissue cells, ensures adequate immunological function, and, during disease, delivers therapeutic drugs to target cells. It consists of the smallest blood vessels: arterioles, capillaries and venules [1] (Fig. 1). Previous techniques for studying microcirculation (microscopes, laser Doppler and plethysmography) were able to provide only global measurements of microvascular blood flow, expressed as average values of the diameter or direction of a single vessel. Recent technological developments using orthogonal polarisation spectral (OPS) imaging techniques allow the direct visualisation and monitoring of microcirculation at the bedside [2], [3] (Fig. 2). The OPS imaging technology is a non-invasive method for directly visualising multiple conditions of the microcirculation that have clinical applications for humans. It allows the quantitative measurement of the diameter of vessels, the velocity of red blood cells and functional capillary density [4]. The technique uses a linearly polarised light to illuminate the area of interest. The light is reflected from the tissue source and forms an image of the illuminated region within the target of the video camera. The image is then captured through a polariser, which is oriented orthogonally to the plane of the illuminating light [5].