NIRS on a functional scale of 0-100%: Establishing practicality of the Moxy Monitor for sport science

Feldmann, Andri Matthias; Erlacher, Daniel; Schmitz, Roger (3 June 2019). NIRS on a functional scale of 0-100%: Establishing practicality of the Moxy Monitor for sport science (Unpublished). In: European College of Sport Science. Prague, CZ. 03.-06.07.2019.

Near-infrared spectroscopy (NIRS) has become readily available technology to monitor muscle oxygenation (SmO2) in applied sport settings. However, the technology is limited by its inability to convey quantifiable values, but rather offers relative change of oxy- and deoxyhemoglobin (O2Hb, HHb). In order to generate robustness for inter-individual and inter-location analysis and comparison an arterial occlusion method (AOM; 1) can be applied to generate a functional scale of 0-100%. On this scale 0% represents a maximally deoxygenated state defined by a disappearance of O2Hb in relation to the sum of O2Hb and HHb, and 100% a maximally oxygenated state and the disappearance of HHb to the sum. The purpose of this study is to examine the practicality and reliability of an a priori determined 0-100% scale by a commercially available NIRS device, the Moxy Monitor (Fortiori Designs LLC, US), using the AOM.
22 participants completed a series of tests to scrutinize the a priori 0-100% scale modeled by the device. First, reliability was tested with AOM in back to back weeks. Then the feasibility of the 0-100% scale was tested firstly by comparing the AOM during passive and active conditions, and secondly by comparing the results for minimally and maximally obtained SmO2 (SmO2min and SmO2max) to a priori defined limits from invasive measurement results of mixed venous oxygen saturation (SvO2). Four devices were mounted on participant’s legs.
The reliability test resulted in significant equivalency between all trials for SmO2min, TOST: -5.38 to 4.62, t(54) = 4.85, p < 0.001, and SmO2max, TOST: -6.13 to 3.87, t(55) = -3.5, p < 0.001.The 0-100% functional scale showed a good dynamic range for all muscle groups (Mmin = 10.1%±5.7; Mmax = 78.1%±6.0). During active and passive conditions the results for SmO2min were significantly equivalent, TOST: -7.69 to 2.32, t(39) = 2.77, p = 0.004. Tested against the a priori defined limits of SvO2, SmO2min was significantly lower than the SvO2 limit of 26% (2), t(54) = -20.69, p < 0.001; as was SmO2max, t(54) = -8.53, p < 0.001, for the SvO2 limit of 85%(3), as predicted.
The device exhibits an appropriate a priori defined functional scale between 0-100% that can be consider reliable and functional for application in sport.
1. Hamaoka, T., et al. (2007). Near-infrared spectroscopy/imaging for monitoring muscle oxygenation and oxidative metabolism in healthy and diseased humans. Journal of Biomedical Optics, 12(6), 062105.

2. Hamaoka, T., et al. (2000). Quantification of ischemic muscle deoxygenation by near infrared time-resolved spectroscopy. Journal of Biomedical Optics, 5(1), 102.

3. Langham, M. C., et al. (2010). Evaluation of Cuff-Induced Ischemia in the Lower Extremity by Magnetic Resonance Oximetry. Journal of the American College of Cardiology, 55(6), 598–606.

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