Key result
A two-element Windkessel model provided a superior fit to middle cerebral artery flow velocity responses during transient blood pressure changes compared with a single-resistance model (P<0.005).
The arterial Windkessel properties significantly contribute to low-frequency cerebral hemodynamic responses during transient blood pressure changes, indicating that these responses are not solely due to active cerebral autoregulation.
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Windkessel effects should be modeled in cerebral flow analyses; leaves open impact on clinical autoregulation assessment.
The Windkessel properties of the vasculature are known to play a significant role in buffering arterial pulsations, but their potential importance in dampening low-frequency fluctuations in cerebral blood flow has not been clearly examined. In this study, we quantitatively assessed the contribution of arterial Windkessel (peripheral compliance and resistance) in the dynamic cerebral blood flow response to relatively large and acute changes in blood pressure. Middle cerebral artery flow velocity (MCA(V); transcranial Doppler) and arterial blood pressure were recorded from 14 healthy subjects. Low-pass-filtered pressure-flow responses (<0.15 Hz) during transient hypertension (intravenous phenylephrine) and hypotension (intravenous sodium nitroprusside) were fitted to a two-element Windkessel model. The Windkessel model was found to provide a superior goodness of fit to the MCA(V) responses during both hypertension and hypotension (R² = 0.89 ± 0.03 and 0.85 ± 0.05, respectively), with a significant improvement in adjusted coefficients of determination (P < 0.005) compared with the single-resistance model (R² = 0.62 ± 0.06 and 0.61 ± 0.08, respectively). No differences were found between the two interventions in the Windkessel capacitive and resistive gains, suggesting similar vascular properties during pressure rise and fall episodes. The results highlight that low-frequency cerebral hemodynamic responses to transient hypertension and hypotension may include a significant contribution from the mechanical properties of vasculature and, thus, cannot solely be attributed to the active control of vascular tone by cerebral autoregulation. The arterial Windkessel should be regarded as an important element of dynamic cerebral blood flow modulation during large and acute blood pressure perturbation.
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Chan et al. (2011) studied Healthy subjects (n=14). Two-element Windkessel model vs. Single-resistance model was evaluated on Goodness of fit (R²) to middle cerebral artery flow velocity responses (p=<0.005). A two-element Windkessel model provided a superior fit to middle cerebral artery flow velocity responses during transient blood pressure changes compared with a single-resistance model (P<0.005).
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