On laser Doppler flowmetry : methods and microvascular applications

Abstract: A laser Doppler flowmeter for non-invasive microcirculatory blood flow studies has been developed. The tissue under study is illuminated by laser light (helium-neon laser, output power 2 mW) via an optical fibre and the Doppler shift oflight scattered in moving red cells is analysed. By the use of two photodetectors for detection of the backscattered light, the influences of mode interference and broadband noise from the laser and noise from surrounding light sources have been suppressed. The instrument is designed to give a continuous, stable and linear real-time measure of the flux of red cells (i.e. the number of red cells times their velocity) in the outermost layer (1 mm) of tissue, in which the red cell volume fractions are low or moderate. Linearity, measuring depth and the influence of blood oxygen tension were evaluated in a flow model with optical properties similar to those of human skin. Laser Dopplerflowmetry was found to be versatile for measurements of blood flow in human skin and rat testis and did not influence the flow under study.An extensive study of spatial and temporal variations of human skin blood flow was performed. As it was found that skin blood flow shows wide day-to-day variations and significant differences between adjacent probe sites, earlier reported "normal" values of skin blood flow were seriously questioned. It is proposed that this study can serve as a base for further functional studies.Testicular blood flow in rats was studied in order to evaluate acute effects of stress-linked substances such as adrenaline and noradrenaline. Both substances lowered the blood flow at high doses.Rhythmical variations of blood flow (frequency 5-12 min-1) in human skin and rat testis were observed and found to be in agreement with earlier findings in microscopic studies on other types of tissue. The nature and origin of this rhythmicity point towards a local regulatory mechanism operating also under "steady state" conditions.