Department of Sports Medicine for Health Promotion, Tokyo Medical University, Tokyo, JAPAN.
Med Sci Sports Exerc. 2021 Apr 1;53(4):853-859. doi: 10.1249/MSS.0000000000002530.
Near-infrared spectroscopy (NIRS), performed with a commonly available noninvasive tissue oxygenation monitoring device, is based on the modified Beer-Lambert law (MBLL). Although NIRS based on MBLL (NIRSMBLL) assumes that the optical path length (PL) is constant, the effects of changes in PL during exercise on muscle oxygenation calculated by MBLL are still incompletely understood. Thus, the purposes of this study were to examine the changes in optical properties during ramp incremental exercise and to compare muscle oxygen dynamics measured by time-resolved NIRS with those calculated based on MBLL.
Twenty-two healthy young men performed ramp incremental cycling exercise until exhaustion. Optical properties (reduced scattering coefficient and PL) and absolute oxygenated, deoxygenated, and total hemoglobin and myoglobin concentrations (oxy[Hb + Mb], deoxy[Hb + Mb], and total[Hb + Mb], respectively) at the vastus lateralis were continuously monitored by a three-wavelength (763, 801, and 836) time-resolved NIRS device. The values of oxy-, deoxy-, and total[Hb + Mb] were then recalculated by assuming constant PL.
PL at all wavelengths statistically significantly shortened during exercise. In particular, PL at 763 nm was greatly shortened, and the average changes during exercise were a 9.8% ± 3.1% reduction. In addition, significant differences in the kinetics of oxy-, deoxy-, and total[Hb + Mb] between directly measuring PL and assuming constant PL were found. The average changes in measured PL and assuming constant PL-deoxy[Hb + Mb] were increases of 28.8 ± 16.0 μM and increases of 16.4 ± 9.3 μM, respectively.
Assuming constant PL in NIRSMBLL significantly underestimated actual muscle oxy/deoxygenation as compared with measurements obtained by real-time PL determination. The percent degree of the underestimated oxy/deoxygenation was greater than the percent degree of the changes in PL.
近红外光谱（NIRS）使用常用的无创组织氧合监测设备进行，基于修正的 Beer-Lambert 定律（MBLL）。尽管基于 MBLL 的 NIRS（NIRSMBLL）假设光程（PL）是恒定的，但在运动过程中 PL 变化对 MBLL 计算的肌肉氧合的影响仍不完全清楚。因此，本研究的目的是检查斜坡递增运动过程中光学特性的变化，并比较时间分辨 NIRS 测量的肌肉氧动力学与基于 MBLL 计算的结果。
22 名健康年轻男性进行斜坡递增自行车运动直至力竭。采用三波长（763、801 和 836nm）时间分辨 NIRS 设备连续监测股外侧肌的光学特性（散射系数和 PL）以及绝对氧合、脱氧和总血红蛋白和肌红蛋白浓度（oxy[Hb+Mb]、deoxy[Hb+Mb]和 total[Hb+Mb]）。然后，假设 PL 恒定，重新计算 oxy-、deoxy-和 total[Hb+Mb]的值。
所有波长的 PL 在运动过程中均呈统计学显著缩短。特别是，763nm 处的 PL 缩短幅度较大，运动过程中的平均变化为 9.8%±3.1%的降低。此外，还发现了直接测量 PL 和假设恒定 PL 之间 oxy-、deoxy-和 total[Hb+Mb]动力学的显著差异。测量 PL 和假设恒定 PL-deoxy[Hb+Mb]的平均变化分别为增加 28.8±16.0μM 和增加 16.4±9.3μM。
与实时 PL 测定相比，在 NIRSMBLL 中假设 PL 恒定会显著低估实际肌肉的氧合/去氧合程度。低估的氧合/去氧合程度百分比大于 PL 变化的百分比。
