Comparison between Spontaneous Low‐Frequency Oscillations in Regional Cerebral Blood Volume, and Cerebral and Plethysmographic Pulsations

The brain plays a crucial role in maintaining systemic functions. Hence, the cerebral circulation is important because the tissue in the brain cannot store energy sources within it and has to constantly obtain them with oxygen from the blood flow. The mean cerebral blood flow is kept constant over a wide range of blood pressure levels by the regulation of the cerebral circulation. However, the regional cerebral blood flow (rCBF) and volume (rCBV) exhibit strong low‐frequency oscillations (LFOs) such as arterial blood pressure and heart rate, which may reflect the interaction of the cerebral and systemic circulation. To gain an insight into the regulation of the cerebral circulation, we investigated LFOs in the rCBV, cerebral pulsation (CP) and plethysmographic pulsation (PP) particularly on their spectral properties. The rCBV and PP signals were simultaneously measured by optical topography (OT: multi‐channel near infra‐red spectroscopy) and plethysmography with the subject in a resting, seated state. The CP signals were obtained from the pulsatile component contained in the OT signals. When we compared the spectra of LFOs, we found that the spectral peak for LFOs tended to distinctly appear in the order of rCBV, PP, and CP. This distinctness might reflect the regulation of the cerebral circulation. OT signals are considered to contain a contribution from the skin tissue. We also demonstrate that CP is different from the pulsation observed from the skin tissue.