Low-frequency harmonics in inlet flow rate play a crucial role in inducing flow instabilities in terminal cerebral aneurysms

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<p>Prediction of rupture status in cerebral aneurysms remains challenging for clinicians, and the important rupture indicator (wall shear stress, WSS) is controversially discussed. Recent studies report that flow instabilities appear to play an influential role in the evolution and rupture of aneurysms and it is strongly correlated with both geometries and inlet flow rate waveforms. However, how frequency harmonics in inlet flow rate waveforms influence the flow instabilities and hence WSS fluctuations in cerebral aneurysms are still unclear. In this study, we used a computational fluid dynamic (CFD) model of anatomically realistic cerebral aneurysms combining with Fourier series and power spectral density (PSD) analysis to investigate the association between inflow waveform's harmonic frequencies and flow fluctuations in terminal cerebral aneurysms. Our simulated results demonstrated that there exists a harmonic frequency dependency in inlet flow rate waveforms inherently associated with flow instabilities in cerebral aneurysms: low-frequency harmonics play a crucial role in causing significant WSS fluctuations. This is partly explained by that the low-frequency harmonics govern a primary local adverse pressure gradient at late systole during flow deceleration, which induces flow instabilities while giving it sufficient time to develop into flow instabilities whereas high-frequency harmonics do not but decay rapidly. This implies that flow fluctuations in cerebral aneurysms may be of some robustness, dependent mainly on the primary harmonic frequency initiated by heart contraction but against unpredictable high-frequency perturbations in the inflow waveforms.</p>

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