A modified fluorescent microsphere-based approach for determining resting and hyperemic blood flows in individual murine skeletal muscles

The goal of this study was to develop a modified fluorescent microsphere-based approach for measuring resting and hyperemic blood flows in individual mouse skeletal muscles. Absolute resting blood flow in the left gracilis posterior was 1.04 ± 0.12 ml·min− 1·g− 1, while functional hyperemia following muscle activity was 5.94 ± 1.33 ml·min− 1·g− 1. Measuring absolute blood flow requires sampling arterial blood that serves as a flow-rate and concentration reference to the fluorescent microsphere (FMS) content in the tissue-of-interest for calculating the flow value. Because sampling arterial blood can impair cardiovascular function in the mouse, we also modified our FMS approach to determine relative blood flows in the left gracilis posterior by using the contralateral muscle as our reference in blood flow calculations. Absolute and relative hyperemia measurements detect similar increases in blood flow — 521.93 ± 216.76% and 555.24 ± 213.82%, respectively. However, sampling arterial blood during absolute blood flow measurements significantly decreased mean arterial pressure from the beginning to the end of our experiments, from 102.7 ± 2.18 to 75.5 ± 9.71 mm Hg. This decrease was not seen when measuring relative blood flows. This approach provides critical advantages over contemporary blood flow measurement approaches by allowing blood flow measurements in small and non-superficial tissues.