Abstract Cerebral blood flow is stabilized through dynamic adjustments across both macro‐ and microvascular compartments. While dynamic cerebral autoregulation (dCA) quantifies upstream pressure–flow coupling, downstream microvascular responses are less well characterized and may represent a distinct but functionally linked process. This study tested whether a two‐component cascade model, treating dCA and an empirically derived index of microvascular function (MF) as sequential stages can represent the integrated regulation of cortical oxygenation. Data from 41 healthy adults (20–45 years) were analysed. Beat‐to‐beat mean arterial pressure (MAP), middle cerebral artery flow velocity (CBFV) and cortical oxyhaemoglobin (O 2 Hb) were recorded during supine spontaneous oscillations and forced oscillations at 0.05 Hz using repeated sit–stand manoeuvres. Transfer function analysis quantified frequency‐domain gain, phase and coherence for MAP→CBFV (dCA), CBFV→O 2 Hb (MF) and MAP→O 2 Hb (total pathway). The cascade model was computed as the product of dCA and MF transfer functions. The cascade model derived indices showed strong correlations with total pathway gain, phase and coherence measures during both spontaneous and forced oscillations, with improved linear coupling under forced oscillations. These results support the applicability of a two‐component cascade model for integrated cerebrovascular regulation and suggest that serial interactions between macrovascular and microvascular regulatory mechanisms jointly shape the frequency‐dependent propagation of arterial pressure to brain‐tissue oxygenation dynamics. image Key points Cerebral blood flow is stabilized by coordinated regulation across large arteries and microvessels, but their dynamic interaction has not been experimentally modelled. We examined whether a two‐component cascade model linking upstream dynamic cerebral autoregulation and downstream microvascular function can explain how blood pressure oscillations influence cortical oxygenation. In 41 healthy adults, we recorded beat‐to‐beat blood pressure, middle cerebral artery blood flow velocity and near‐infrared spectroscopy‐derived oxygenation during rest and sit–stand manoeuvres, and analysed them using transfer function analysis. Gains, phases and coherences derived from the cascade model closely matched those from the direct blood pressure–O 2 Hb relationship, particularly under forced oscillations during sit–stand, demonstrating the model's physiological relevance. The cascade model provides a mechanistic framework to separate and quantify large‐ and small‐vessel contributions to cerebral blood flow regulation, with potential application in future studies of ageing and cerebrovascular disease.
Kurazumi et al. (Wed,) studied this question.