The measurement of pressure and flow in the microcirculation: application to physiological and clinical problems.

The analysis of hemodynamic phenomena at the level of microscopic blood vessels of diameters ranging from 10(-2)-10(-3) cm is currently based on direct measurements of plasma pressure and red blood cell velocity in in-vivo conditions. Pressure measurements are performed with active pressure measurement systems via cannulae with 1 mum tip openings. Flow measurements are deduced from optical transit time methods from data recorded by television. The technique provides both average and dynamic data. The latter is derived from signal processing of the direct measurements by means of active filters. These techniques yield data on low level signals related to the periodic action of the heart. This analysis provides information on the transit time of pressure and flow pulses through the microcirculation. These methods are currently utilized in routine physiologic investigations and as a means for studying the human skin microcirculation of normal subjects.