Non-invasive Hyperspectral Multi-distance Measurements of Cerebral Response to Breath Holding in Adult Humans
Vladislav Toronov, 1,2, Zahida Guerouah, 1
1 Ryerson University, 350 Victoria Street Toronto, Ontario M5B 2K3, Canada
2 Institute of Biomedical Engineering, Science and Technology (iBEST), Li Ka-Shing Knowledge Institute, 7th Floor, LKS 735
209 Victoria Street, Toronto, ON, M5B 1T8, Canada
Abstract
Similar to the controlled fusion, non-invasive near-infrared spectroscopy of the human brain has been a hot topic of research for decades. In spite of the huge advantages for the clinical bedside monitoring and diagnosis of the brain, the main obstacle - the severe biasing from the extra-cerebral tissues in adults - still has to be resolved. This includes the optimization of the source-detector distances, wavelengths, spectroscopy modality (time-domain, frequency-domain, or hyperspectral), and signal processing techniques. The goal of our present study was to measure the true cerebral response in adult human subjects to breath holding. On the one hand, the breath holding is a simple method to simulate conditions common to many clinical situations when not only the brain but the entire human body exhibits severe hemodynamic changes. On the other hand, breath holding was proposed as a diagnostic paradigm to assess the cerebrovascular reactivity, which is an important measure of the cerebral blood flow autoregulation. In this study we measured cerebral responses to breath holding in the near-infrared range between 700 nm and 1000 nm by three highly sensitive spectrometers simultaneously at source-detector distances of 1 cm, 3cm, and 4 cm. This allowed us to assess the wavelength dependence of the responses across the wide near-infrared waveband, to analyze in detail the contribution of the extra-cerebral tissues at different wavelengths, and to analyze the responses to breath holding both in hemoglobin and in cytochrome C oxidase redox (CCOr), which is the direct marker of tissue oxygen metabolism. Using the advanced signal processing and statistical analysis we have found that only CCOr at 4 cm provides the true cerebral response without using measurements at short source-detector separation. When using the short-distance measurements to clean the signals from the extra-cerebral contamination the cerebral responses also can be revealed in the hemoglobin responses at 3 and 4 cm. These results will allow to develop a near-infrared cerebral monitor with minimal extra-cerebral biasing.
Speaker
Vladislav Toronov
X University
Canada
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