Phase characterization of oscillatory components of the cerebral concentrations of oxy-hemoglobin and deoxy-hemoglobin

摘要

We present a study of the relative phase of oscillations of cerebral oxy- and deoxy-hemoglobin concentrations in the low-frequency range, namely 0.04-0.12 Hz. We have characterized the potential contributions of noise to the measured phase distributions, and we have performed phase measurements on the brain of a human subject at rest, and on the brain of a human subject during stage I sleep. While phase distributions of pseudo hemodynamic oscillations generated from noise (obtained by applying to two independent sets of random numbers the same linear transformation that converts absorption coefficients at 690 and 830 nm into concentrations of oxy- and deoxy-hemoglobin) are peaked at 180°, those associated with real hemodynamic changes can be peaked around any value depending on the underlying physiology and hemodynamics. In particular, preliminary results reported here indicate a greater phase lead of deoxy-hemoglobin vs. oxy-hemoglobin low-frequency oscillations during stage I sleep (82° ± 55°) than while the subject is awake (19° ± 58°).