Diffuse Light Quantification of Blood Flow, Oxygenation and Metabolism in Human Skeletal Muscle

Abstract

The lack of portable, noninvasive technologies for continuously monitoring hemodynamics in the deep microcirculation has led us to develop a hybrid instrument combining near-infrared diffuse correlation spectroscopy (DCS) and diffuse reflection spectroscopy (DRS). PURPOSE: To describe results of first clinical studies applying this instrument to simultaneously measure blood flow and oxygenation in cuffed or exercising muscle. The ultimate aim is to provide multiple hemodynamic parameters for evaluation of microcirculation and tissue metabolism in the patients with peripheral arterial disease (PAD). METHODS: DCS monitors relative blood flow (rBF) by measuring the optical phase shifts caused by moving blood cells, while DRS measures tissue absorption and scattering to calculate tissue oxygen saturation (StO2) and total hemoglobin concentration (THC). Relative muscle oxygen consumption (rVO2) was also computed from these data. Nine healthy legs and nine patient legs with PAD were studied during 3-minute arterial cuff occlusion of arm and leg, and during 1 -minute plantar flexion exercise. RESULTS: Signals from different layers (cutaneous tissues and muscles) during occlusion were differentiated, revealing strong hemodynamic responses from muscle layers. During exercise in healthy legs, the observed ∼4.7 fold rBF increase was significantly lower than the ∼7 fold rVO2 increase, thus resulted in a gradual StO2 decrease (Maximum ΔStO2 = ∼ −19%). We were able to distinguish features differentiating normal and diseased responses. For example, the rBF increases in PAD patients during exercise were significantly lower than those in controls, and the recovery times of StO2 and rBF following occlusion were significantly longer than those of controls. A correlation between the magnitude of reactive hyperemia following occlusion and ABI value was also found from 9 diseased legs. Lower magnitude of reactive hyperemia associated with lower value of ABI, indicating severe disease. CONCLUSION: DCS has been shown, for the first time, to be capable of penetration through layers of upper tissues reaching the muscle tissue. The combination of DCS and DRS has allowed us, for the first time, to use all-optical methods noninvasively and continuously, to measure multiple hemodynamic parameters in deep muscle tissues. The hybrid system can improve the noninvasive technology currently available to study the microcirculation. Diseases that affect blood flow to the microcirculation, such as in PVD, are promising areas for application of our instrument.