Diffuse Optical Spectroscopy Assessment of Resting Oxygen Metabolism in the Leg Musculature

Abstract

We lack reliable methods to continuously assess localized, resting-state muscle activity that are comparable across individuals. Near-infrared spectroscopy (NIRS) provides a low-cost, non-invasive means to assess localized, resting-state muscle oxygen metabolism during venous or arterial occlusions (VO2VO and VO2AO, respectively). However, this technique is not suitable for continuous monitoring, and its utility is limited to those who can tolerate occlusions. Combining NIRS with diffuse correlated spectroscopy (DCS) enables continuous measurement of an index of muscle oxygen metabolism (VO2i). Despite the lack of previous validation, VO2i is employed as a measure of oxygen metabolism in the muscle. Here we characterized measurement repeatability and compared VO2i with VO2VO and VO2AO in the medial gastrocnemius (MG) in 9 healthy adults. Intra-participant repeatability of VO2i, VO2VO, and VO2AO were excellent. VO2i was not significantly correlated with VO2AO (p = 0.15) nor VO2VO (p = 0.55). This lack of correlation suggests that the variability in the calibration coefficient between VO2i and VO2AO/VO2VO in the MG is substantial across participants. Thus, it is preferable to calibrate VO2i prior to every monitoring session. Important future work is needed to compare VO2i against gold standard modalities such as positron emission tomography or magnetic resonance imaging.

Exercise Training Increases Resting Calf Muscle Oxygen Metabolism in Patients with Peripheral Artery Disease

“…Our average pre-exercise StO 2 of 66.2 ± 7.5% (mean ± SD) is within the range of FD-DOS calf muscle measurements reported in the literature for PAD patients, e.g., 68 ± 6% [32] and 56 ± 16% [33], as well as for healthy adults, e.g., 72.7 ± 3.2% [31], 55.5 ± 9.9% [30], 62 ± 5% [34], 66.2 ± 11.4% [33], 72.0 ± 4% [32]. Our average THC of 106 ± 31 µM is within the range of previous FD-DOS calf muscle measurements performed in PAD patients, i.e., 68 ± 22 µM [32], and in healthy adults, i.e., 62 ± 21 µM [34], 48 ± 18 µM [30]. Finally, our average pre-exercise γ of 0.77 ± 0.18 in the calf muscle is similar to previous estimates of γ in the brain, i.e., 0.84 ± 0.21 [23].…”

“…Our average pre-exercise resting calf muscle oxygen metabolism measurements of 2.74 (2.24, 3.40) µmol/100 mL/min (or 0.06 (0.05, 0.07) mL/100 g/min) are roughly consistent with previous measurements of resting calf muscle oxygen metabolism in PAD patients (e.g., 0.05 (0.03, 0.07) mL/100 g/min [28], 0.10 (0.04, 0.16) mL/100 g/min [29]). They are also on a similar scale to previously reported resting calf muscle oxygen metabolism measurements in healthy adults, e.g., 0.03 (0.02, 0.05) mL/100 g/min [30], 0.05 (0.03, 0.06) mL/100 g/min [31], 0.04 (0.03, 0.06) mL/100 g/min [28].…”

“…Fourth, variance in the adipose/skin thickness above the muscle can influence the absolute optical measurements [24,30,36]. Our primary conclusions, though, are based on relative changes, and the excellent intra-subject repeatability of calf muscle oxygen metabolism measurements observed in healthy adults [30] suggests that relative changes are robust to these effects.…”

“…Fourth, variance in the adipose/skin thickness above the muscle can influence the absolute optical measurements [24,30,36]. Our primary conclusions, though, are based on relative changes, and the excellent intra-subject repeatability of calf muscle oxygen metabolism measurements observed in healthy adults [30] suggests that relative changes are robust to these effects. Finally, the mechanism by which exercise improves outcome is multifactorial [7], and future work is needed to elucidate whether enhanced muscle oxidative metabolism is a key factor behind exercise-induced improvement in claudication symptoms.…”

Combined Monte Carlo and k-Wave Simulations for Reconstruction of Blood Oxygen Saturation in Optoacoustics: A Pilot Study

“…Optical imaging techniques [5,6] benefit from both non-invasiveness and high sensitivity to blood oxygenation owing to significant difference in absorption spectra of oxy-and deoxyhemoglobin in optical spectral range. Traditionally, blood oxygenation level is estimated with diffuse optical spectroscopy (DOS) [2,7,8] based on the registration of the spectra of the probing radiation passed through the biological tissue and the subsequent reconstruction of the medium absorption spectra from the measurement data [9,10]. This approach, however, provides with the estimation of blood oxygenation value averaged over a particular measurement volume within biological tissue.…”