A major limitation of near-infrared spectroscopy (NIRS) is its high sensitivity to the scalp and low sensitivity to the brain of adult humans. In the present work we used multi-distance hyperspectral NIRS (hNIRS) to investigate the optimal source-detector distances, wavelength ranges, and analysis techniques to separate cerebral responses to 30 s breath-holds (BHs) from the responses in the superficial tissue layer in healthy adult humans. We observed significant responses to BHs in the scalp hemodynamics. Cerebral responses to BHs were detected in the cytochrome C oxidase redox (rCCO) at 4 cm without using data from the short-distance channel. Using the data from the 1 cm channel in the two-layer regression algorithm showed that cerebral hemodynamic and rCCO responses also occurred at 3 cm. We found that the waveband 700–900 nm was optimal for the detection of cerebral responses to BHs in adults.

Near Infrared Spectroscopy (NIRS) uses near infrared light to measure the concentrations of different tissue chromophores such as oxygenated hemoglobin (HbO2), deoxygenated hemoglobin (HHb), and cytochrome c oxidase (Cyt-ox). However, NIRS measurements in adult humans are highly sensitive to extracranial tissue layers and thus less sensitive to the brain. The aim of this work was to assess the effectiveness of measuring specific brain hemodynamic response during breath-holding respiratory challenge. We used hyperspectral NIRS with combined short and long source-detector distance channels at 1 cm, 3 cm, and 4 cm. We used two approaches for signal processing: we measured the absolute hemoglobin concentrations using the analytical solution to the light diffusion equation for the semi-infinite homogeneous medium, and the changes in tissue layers using the modified Lambert-Beer law for a two-layer medium. Linear regression in the time domain of long distance and short distance channel signals allowed us to assess differences in brain responses and extracranial changes. We found that using the short-range channel was important for measuring cerebral response to breath-holding. We also found that the optimal wavelength band was between 750 and 900 nm, with the largest partial change between 800 and 850 nm. We also found that Cyt-ox at the 4 cm channel exhibited the most brain-specific changes compared to HbO2 and HHb.

Near Infrared Spectroscopy (NIRS) uses near infrared light to measure the concentrations of different tissue chromophores such as oxygenated hemoglobin (HbO2), deoxygenated hemoglobin (HHb), and cytochrome c oxidase (Cyt-ox). However, NIRS measurements in adult humans are highly sensitive to extracranial tissue layers and thus less sensitive to the brain. The aim of this work was to assess the effectiveness of measuring specific brain hemodynamic response during breath-holding respiratory challenge. We used hyperspectral NIRS with combined short and long source-detector distance channels at 1 cm, 3 cm, and 4 cm. We used two approaches for signal processing: we measured the absolute hemoglobin concentrations using the analytical solution to the light diffusion equation for the semi-infinite homogeneous medium, and the changes in tissue layers using the modified Lambert-Beer law for a two-layer medium. Linear regression in the time domain of long distance and short distance channel signals allowed us to assess differences in brain responses and extracranial changes. We found that using the short-range channel was important for measuring cerebral response to breath-holding. We also found that the optimal wavelength band was between 750 and 900 nm, with the largest partial change between 800 and 850 nm. We also found that Cyt-ox at the 4 cm channel exhibited the most brain-specific changes compared to HbO2 and HHb.