Cerebral hemodynamics: a mathematical model including autoregulation, baroreflex and extracranial peripheral circulation

Abstract

Increasing evidence supports that cerebral autoregulation and mean arterial pressure regulation via baroreflex contribute to cerebral blood flow regulation. It is unclear whether the extracranial vascular bed of the head and neck helps reestablishing cerebral blood flow during changes in mean arterial pressure. Current computational models of cerebral blood flow regulation do not address the relationships between the intracranial and extracranial blood flow dynamics. We present a model of cerebral autoregulation, extracranial peripheral circulation and baroreflex control of heart rate and of peripheral vasculature that was included to the model of intracranial dynamics proposed by Linninger et al. (2009), which incorporates the fully coupled blood, cerebrospinal fluid and brain parenchyma systems. Autoregulation was modelled as being pressure-mediated at the arteries and arterioles and flow-mediated at the microcirculation. During simulations of a bout of acute hypotension, cerebral blood flow returns rapidly to baseline levels with a very small overshoot, whereas the blood flow to the peripheral circulation of the head and neck suffers a prolonged suppression in accordance with experimental evidence. The inclusion of baroreflex regulation at the extracranial vascular bed had a negligible effect on cerebral blood flow regulation during dynamic changes in mean arterial pressure. Moreover, the results suggest that the extracranial blood flow carries only modest information about cerebral blood flow in dynamic situations in which cerebral autoregulation is preserved and mean arterial pressure suffers alterations. This information is likely higher when the autoregulation is impaired. Steady-state cerebral blood flow in the model is kept within normal ranges despite variations in mean arterial pressure from 50 to 175 mmHg. By inputting aortic pressure waves from individuals with increasing arterial rigidity, increasing arterial systolic and pulse pressures, the model predicts the generation of intracranial pressure waves with accordingly increasing peaks and amplitudes.