Abstract
The measurement of skeletal muscle oxygenation by NIRS methods is obstructed by the subcutaneous adipose tissue which might vary between < 1 mm to more than 12 mm in thickness. A new algorithm is developed to minimize the effect of this lipid layer on the calculation of muscle haemoglobin / myoglobin concentrations. First, we demonstrate by comparison with ultrasound imaging that the optical lipid signal peaking at 930 nm is a good predictor of the adipose tissue thickness (ATT). Second, the algorithm is based on measurements of the wavelength dependence of the slope ΔA/Δρ of attenuation A with respect to source detector distance p and Monte Carlo simulations which estimate the muscle absorption coefficient based on this slope and the additional information of the ATT. This method is tested on experimental data measured on the vastus lateralis muscle of volunteers during an incremental cycling exercise during normal and hypoxic conditions (corresponding to 0, 2000 and 4000 m altitude). The experimental setup uses broad band detection between 700 and 1000 nm at six source-detector distances. We demonstrate that the description of the experimental data is improved and the calculated changes in oxygen saturation are markedly different when the ATT correction is included.
© 2006 Optical Society of America
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