Laser-Doppler Continuous Real-Time Monitor of Pulsatile and Mean Blood Flow in Tissue Microcirculation

Abstract

A noninvasive instrument capable of instantaneous (~ 30 msec resolution) and continous evaluation of local flow in tissue microcirculation has been developed based on laser Doppler velocimetry. Laser light is delivered to and detected from the region to be studied by flexible, graded-index fiber optic light guides. The Doppler-broadening of laser light scattered by moving red blood cells within the tissue is analyzed in real-time by an analogue processor which provides a continuous output of the instantaneous mean Doppler frequency in the photocurrent detected by a square-law detector. The mean Doppler frequency is predicted by theory to be linearly correlated with microcirculatory blood flow in a variety of tissues, and the Laser-Doppler signal has been correlated with measurements of average tissue blood flow by other techniques. The local spatial ensemble of moving red blood cells within lmm³ of the microcirculation allows an instantaneous assessment of flow pulsations during the cardiac cycle as well as slower changes in average flow. The instrument has been designed to facilitate simple rapid clinical measurements of local spatial and temporal variations in microcirculatory flow. Measurement of local tissue blood flow in normal volunteers and patients has demonstrated the ease of accurately measuring basal and perturbed flow (reactive hyperemia, thermal hyperemia, position changes).