Measuring microlymphatic flow using fast video microscopy -: art. no. 064016

Despite advances in the measurement of lymphatic function, little is known about the actual velocities of flow in microlymphatic (similar to 100 mu m diam) vessels. In this work, video microscopy and particle tracking methods are adapted and integrated with an ultra-highspeed imaging camera to obtain measurements of lymph velocities throughout the entire lymphatic contraction cycle in the rat mesentery, something that previous systems were incapable of measuring. To determine the system's accuracy, calibration experiments are conducted across the hypothesized physiologically significant range of velocities for microlymphatic flow (up to 15 mm/sec). The system shows high accuracy, less than 2% error, when comparing actual with measured velocities. Microspheres flowing through 140-mu m-diam tubing are imaged to demonstrate the system's ability to determine flow rates in these small vessels by measuring particle velocities. To demonstrate biological applicability, mesenteric microlymphatics in loops of the small intestine of three male Sprague-Dawley rats are exteriorized and imaged with the high-speed system at a rate of 500 frames/sec for several contraction sequences. Lymph velocity fluctuates cyclically with the vessel wall contractions, ranging from -1 to 7 mm/sec. These rates are higher than would be possible with standard video microscopy (3.75 mm/sec maximum). (C) 2005 Society of Photo-Optical Instrumentation Engineers.