Noninvasive optical quantification of absolute blood flow, blood oxygenation, and oxygen consumption rate in exercising skeletal muscle

Abstract

Abstract. This study investigates a method using novel hybrid diffuse optical spectroscopies [near-infrared spectroscopy (NIRS) and diffuse correlation spectroscopy (DCS)] to obtain continuous, noninvasive measurement of absolute blood flow (BF), blood oxygenation, and oxygen consumption rate ( _ VO 2 ) in exercising skeletal muscle. Healthy subjects (n ¼ 9) performed a handgrip exercise to increase BF and _ VO 2 in forearm flexor muscles, while a hybrid optical probe on the skin surface directly monitored oxy-, deoxy-, and total hemoglobin concentrations ([HbO 2 ], [Hb], and THC), tissue oxygen saturation (S t O 2 ), relative BF (rBF), and relative oxygen consumption rate (r _ VO 2 ). The rBF and r _ VO 2 signals were calibrated with absolute baseline BF and _ VO 2 obtained through venous and arterial occlusions, respectively. Known problems with muscle-fiber motion artifacts in optical measurements during exercise were mitigated using a novel gating algorithm that determined muscle contraction status based on control signals from a dynamometer. Results were consistent with previous findings in the literature. This study supports the application of NIRS/DCS technology to quantitatively evaluate hemodynamic and metabolic parameters in exercising skeletal muscle and holds promise for improving diagnosis and treatment evaluation for patients suffering from diseases affecting skeletal muscle and advancing fundamental understanding of muscle and exercise physiology.

Hybrid diffuse optical techniques for continuous hemodynamic measurement in gastrocnemius during plantar flexion exercise

“…31 This flow index is normalized to an initial period of baseline to produce rBF. 6,9,32 DCS has been validated against multiple techniques, such as Xenon-computed tomography, arterial-spin-labeled MRI, and laser Doppler, 22,25,33 and has proven successful in making rBF measurements of local muscles in the leg and forearm. 6,9,32,[34][35][36] In some of these studies, DCS has been combined with NIRS to form a hybrid DCS/NIRS instrument for making all-optical measurements of both rBF and StO 2 , which allows for the derivation of the relative change of oxygen consumption rate (r _ VO 2 ).…”

“…6,9,32 DCS has been validated against multiple techniques, such as Xenon-computed tomography, arterial-spin-labeled MRI, and laser Doppler, 22,25,33 and has proven successful in making rBF measurements of local muscles in the leg and forearm. 6,9,32,[34][35][36] In some of these studies, DCS has been combined with NIRS to form a hybrid DCS/NIRS instrument for making all-optical measurements of both rBF and StO 2 , which allows for the derivation of the relative change of oxygen consumption rate (r _ VO 2 ). 6,9,22,34 Only recently have occlusion calibrations and gating techniques been applied by our laboratory to allow DCS/NIRS hybrid instruments to simultaneously and continuously measure absolute values of BF, blood oxygenation, and oxygen consumption rate ( _ VO 2 ) in forearm muscles during handgrip exercises.…”

“…6,9,22,34 Only recently have occlusion calibrations and gating techniques been applied by our laboratory to allow DCS/NIRS hybrid instruments to simultaneously and continuously measure absolute values of BF, blood oxygenation, and oxygen consumption rate ( _ VO 2 ) in forearm muscles during handgrip exercises. 9 The translation of these techniques from the arm to the lower limb is the goal of this study as various diseases (such as PAD) affect muscle tissue perfusion and metabolism preferentially in the lower limb. This research then focused on developing calibration and exercise protocols for use in the lower limb that would be comparable to those of literature and, optimally, could be done by both healthy controls and PAD patients.…”

“…[1][2][3][4][5][6][7][8][9] Understanding how the healthy muscle reacts to different perturbations allows researchers and clinicians to evaluate how disease states affect the muscle's performance. Given the complexity of the operation of muscle tissue and the dynamically regulated interplay of local versus global controls of blood perfusion in response to the tissue demand for oxygen, mechanical effects, and aggregation of feedback metabolites, it is no wonder that muscle physiology and diseases thereof remain a highly active field of study.…”

“…6,9,32,[34][35][36] In some of these studies, DCS has been combined with NIRS to form a hybrid DCS/NIRS instrument for making all-optical measurements of both rBF and StO 2 , which allows for the derivation of the relative change of oxygen consumption rate (r _ VO 2 ). 6,9,22,34 Only recently have occlusion calibrations and gating techniques been applied by our laboratory to allow DCS/NIRS hybrid instruments to simultaneously and continuously measure absolute values of BF, blood oxygenation, and oxygen consumption rate ( _ VO 2 ) in forearm muscles during handgrip exercises. 9 The translation of these techniques from the arm to the lower limb is the goal of this study as various diseases (such as PAD) affect muscle tissue perfusion and metabolism preferentially in the lower limb.…”