Measuring microlymphatic flow using fast video microscopy

Despite advances in the measurement of lymphatic function, little is known about the actual velocities of flow in microlymphatic ($∼100μm$ diam) vessels. In this work, video microscopy and particle tracking methods are adapted and integrated with an ultra-high-speed imaging camera to obtain measurements of lymph velocities throughout the entire lymphatic contraction cycle in the ratmesentery, 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 $15mm∕sec$). The system shows high accuracy, less than 2% error, when comparing actual with measured velocities. Microspheres flowing through $140-μm$-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 $500frames∕sec$ for several contraction sequences. Lymph velocity fluctuates cyclically with the vessel wall contractions, ranging from $−1to7mm∕sec$. These rates are higher than would be possible with standard video microscopy ($3.75mm∕sec$ maximum).