Characterization of the ischemic muscle by quantitative hybrid diffuse optical measurement

The ischemia is one of the most common and severe events threatening the function and maintenance of organs and limbs, while there is not ideal non-invasive method to distinguish and quantify the ischemia. The near-infrared light techniques permit noninvasive evaluation of microvascular hemodynamics of muscle, but most of studies measure the relative hemodynamic changes, that is, it needs the same normal tissue from the same subject as the reference measurement. In this study, the quantitative hemodynamic values of the total hemoglobin concentration (HbT), tissue oxygen saturation (StO2) and blood flow index (BFI) were monitored simultaneously by the custom hybrid diffuse optical device based on the combining of near infrared spectroscopy (NIRS) and diffuse correlation spectroscopy (DCS). A vascular occlusion test (VOT) on the forearm was utilized to produce transient controlled ischemia with arm cuff inflated to the pressure of 200 mmHg. The statistical significances (p value) were calculated by the pair sample t-test method and the receiver operator characteristic curves (ROCs) for the derived quantitative hemodynamic parameters between the normal tissue and the ischemic muscle. The results from fifteen subjects show both of the quantitative values of BFI and StO2 can distinguish the ischemia from normal tissue through putting the probe on the muscle tissue without reference measurement. The BFI has best discrimination ability and the optimal condition to derive the BFI is using the assumed same optical properties for all the subjects rather than the derived individual optical properties from each subject. The StO2 can also distinguish the ischemia and the optimal condition to derive the StO2 is using the derived individual reduced scattering coefficient from each subject rather than the assumed same reduced scattering coefficient for all the subjects. Therefore the hybrid diffuse optical device may be better than the usual NIRS device to monitor the state of ischemia of tissue and BFI is the promising biomarker to distinguish and quantify the ischemia.