title: Phase-amplitude investigation of spontaneous low-frequency oscillations of cerebral hemodynamics with near-infrared spectroscopy: a sleep study in human subjects.
abstract: We have investigated the amplitude and phase of spontaneous low-frequency oscillations (LFOs) of the cerebral deoxy- and oxy-hemoglobin concentrations ([Hb] and [HbO]) in a human sleep study using near-infrared spectroscopy (NIRS). Amplitude and phase analysis was based on the analytic signal method, and phasor algebra was used to decompose measured [Hb] and [HbO] oscillations into cerebral blood volume (CBV) and flow velocity (CBFV) oscillations. We have found a greater phase lead of [Hb] vs. [HbO] LFOs during non-REM sleep with respect to the awake and REM sleep states (maximum increase in [Hb] phase lead: ~π/2). Furthermore, during non-REM sleep, the amplitudes of [Hb] and [HbO] LFOs are suppressed with respect to the awake and REM sleep states (maximum amplitude decrease: 87%). The associated cerebral blood volume and flow velocity oscillations are found to maintain their relative phase difference during sleep, whereas their amplitudes are attenuated during non-REM sleep. These results show the potential of phase-amplitude analysis of [Hb] and [HbO] oscillations measured by NIRS in the investigation of hemodynamics associated with cerebral physiology, activation, and pathological conditions.
authors: Department of Biomedical Engineering, Tufts University, Medford, MA, USA. michele.pierro@tufts.edu
authors: Michele L
authors: ML
authors: Pierro
authors: Angelo
authors: A
authors: Sassaroli
authors: Peter R
authors: PR
authors: Bergethon
authors: Bruce L
authors: BL
authors: Ehrenberg
authors: Sergio
authors: S
authors: Fantini
mesh_terms: D001921:Brain / Q000098:blood supply* / Q000502:physiology*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D004569:Electroencephalography; D006439:Hemodynamics / Q000502:physiology*; D006801:Humans; D012890:Sleep / Q000502:physiology*; D019265:Spectroscopy, Near-Infrared