Contribution of arterial Windkessel in low-frequency cerebral hemodynamics during transient changes in blood pressure

• Published in: Journal of applied physiology (1985) Vol. 110; no. 4; pp. 917 - 925
• Main Authors: CHAN, Gregory S. H, AINSLIE, Philip N, WILLIE, Chris K, TAYLOR, Chloe E, ATKINSON, Greg, JONES, Helen, LOVELL, Nigel H, TZENG, Yu-Chieh
• Format: Journal Article
• Language: English
• Published: Bethesda, MD American Physiological Society 01-04-2011
• Subjects: Adult; Biological and medical sciences; Blood Flow Velocity - physiology; Blood pressure; Blood Pressure - physiology; Cerebrovascular Circulation - physiology; Comparative analysis; Electrocardiography; Female; Fundamental and applied biological sciences. Psychology; Hemodynamics - physiology; Humans; Intervention; Male; Middle Cerebral Artery - diagnostic imaging; Middle Cerebral Artery - physiology; Studies; Ultrasonography, Doppler, Transcranial; Veins & arteries; Regional blood flow; Vertebrata; Mammalia; transcranial Doppler; Variability; Central nervous system; cerebral blood flow; Blood pressure; Hemodynamics; Low frequency; Encephalon; cardiovascular variability
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.01407.2010

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.