Mathematical model for the hemodynamic response to venous occlusion measured with near-infrared spectroscopy in the human forearm.

We propose a mathematical model to describe the hemodynamic changes induced by a venous occlusion in a human limb. These hemodynamic changes, which include an increase in blood volume, a reduction in blood flow, and modifications to the oxygen saturation of hemoglobin, can all be measured noninvasively with near-infrared spectroscopy (NIRS). To test the model, we have performed NIRS measurements on the human forearm, specifically on the brachioradialis muscle, during venous occlusion induced by a pneumatic cuff inflated around the upper arm to pressures within the range 10-60 mmHg. We have found a good agreement between parameters measured by NIRS (total hemoglobin concentration and hemoglobin saturation) and the corresponding model parameters (capacitor voltage and arterial/capillary branch current). In particular, model and experiment indicate that the time constant for blood accumulation during venous occlusion (approximately 73-79 s) is much slower than the time constant for blood drainage following cuff release (approximately 5 s). These results indicate that this mathematical model can be a valuable analytical tool to characterize, optimize, and further develop diagnostic measurement schemes that use venous occlusion approaches.