Limb and skeletal muscle blood flow measurements at rest and during exercise in human subjects

The aim of the present review is to present techniques used for measuring b lood flow in human subjects and advice as to when they may be applicable. S ince blood flow is required to estimate substrate fluxes, energy turnover a nd metabolic rate of skeletal muscle, accurate measurements of blood flow a re of extreme importance. Several techniques have therefore been developed to enable estimates to be made of the arterial inflow to, venous outflow fr om, or local blood flow within the muscle. Regional measurements have been performed using electromagnetic flow meters, plethysmography, indicator met hods (e.g. thermodilution and indo-cyanine green dye infusion), ultrasound Doppler, and magnetic resonance velocity imaging. Local estimates have been made using Xe-133 clearance, microdialysis, near i.r. spectroscopy, positr on emission tomography and laser Doppler. In principle, the aim of the stud y, the type of interventions and the limitations of each technique determin e which method may be most appropriate. Ultrasound Doppler and continuous i ndo-cyanine green dye infusion gives the most accurate limb blood flow meas urements at rest. Moreover, the ultrasound Doppler is unique, as it does no t demand a steady-state, and because its high temporal resolution allows de tection of normal physiological variations as well as continuous measuremen ts during transitional states such as at onset of and in recovery from exer cise. During steady-state exercise thermodilution can be used in addition t o indo-cyanine green dye infusion and ultrasound Doppler, where the latter is restricted to exercise modes with a fixed vessel position. Magnetic reso nance velocity imaging may in addition be used to determine blood flow with in deep single vessels. Positron emission tomography seems to be the most p romising tool for local skeletal muscle blood-flow measurements in relation to metabolic activity, although the mode and intensity of exercise will be restricted by the apparatus design.