Laser doppler flowmetry. A new non-invasive measurement of microcirculation in intensive care?

Abstract

Laser doppler flowmetry (LDF) is a new non-invasive technique by which microcirculation changes in tissue can be studied. In recent papers, this technique has been used to measure microflow in standardized fluid models, in animals and in human clinical situations. LDF utilizes the doppler shift, i.e. the frequency (wave length) change that light as well as all waves undergo being reflected by moving objects such as, e.g. red blood cells. A beam of low power laser light (2 mW He-Ne at 632.8 nm) is led by an optical fibre to a measuring head. From here it enters the tissue to which it is applied by a hemisphere with a 1 mm radius. Blood cells traversing this volume are struck by the light and reflect it, whereby the light undergoes a doppler shift. The surrounding tissue also reflects the light, but in an unshifted manner. Thus the volume of illumination is a mixture of an unshifted and a doppler shifted component, the magnitude and frequency of the latter being related to the number of moving cells and their velocity. The measured microflow is proportional to an arbitrary scale (0 to 10). Our own experience with some applications in human clinical situations is described: Normal skin in a control group. Normal skin and burned area in burned patients. Patient in hypothermia with general anesthesia. Patient in shock. LDF seems to be an interesting new non-invasive technique, supplying a good definition of the skin microflow. In the future, this technique could be one of the non-invasive techniques used for intensive care, defining the microcirculation state of a patient.