Although Near Infrared Spectroscopy (NIRS) is a unique non-invasive method to monitor oxygen metabolism in skeletal muscle performance, it is sometimes necessary to monitor blood flow continuously in order to fully understand both oxygen delivery and demand relationship. This article introduces a novel method to continuously monitor blood flow by using information provided by the NIRS of the skeletal muscles. Methods Deoxy (Hb) and Oxyhemoglobin (HbO2), located in the blood of the skeletal muscle, carry two internal relationships between blood flow and oxygen consumption. One is a mass transfer principle (Fick's equation) and the other describes a relationship between oxygen consumption and Hb kinetics in a two-compartment model. To monitor blood flow continuously, we transfer these two relationships into two equations, in order to calculate blood flow with the differential information of HbO2 and Hb. In addition, these equations are used to simulate the relationship between blood flow and reoxygenation kinetics after cuff ischemia and a light exercise. Six healthy subjects volunteered for the cuff ischemia, light arm exercise and arm exercise with cuff ischemia for the experimental study. Results Experimental data of both cuff ischemia and light exercise showed greater blood flow (3 or 4 times that of resting values) during recovery, agreeing with previous findings. Further, the simulation and experimental studies of cuff ischemia and light exercise agreed with each other. Finally, the simulation showed that the high blood flow response after both ischemia and exercise followed a reciprocal relationship to a half-time reoxygenation rate. Conclusion We conclude that kinetics of Hb and HbO2 from cuff ischemia and muscle exercise can provide blood flow information non-invasively with NIRS. Further, this method can be used for simulation as well as blood flow determination. The driven equation can be also used to simulate models for describing the relationship between muscle oxygen status, blood flow and oxygen metabolism.
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