The Cerebral Windkessel as a Dynamic Pulsation Absorber

Abstract

Nearly all cerebrospinal fluid (CSF) flow and cerebral arterial and venous blood flow is pulsatile [1-4]. Capillary blood flow is nearly smooth [5,6,7]. The pulsatility of the CSF closely resembles the pulsatility of the intracranial veins [8,9], both of which have some characteristics of an arterial pulse, including, under some circumstances, a dicrotic notch [10]. Many aspects of the pulsatility of intracranial blood and CSF are difficult to understand, particularly because the pulsatile flow occurs in a rigid cranium which places obvious constraints on pulsatile dynamics. How is it that capillary blood flow is smooth, whereas the blood flow in the intracranial arteries and veins—sometimes only millimeters away from the capillaries— is quite pulsatile [3]? Why does the pulsatility of the veins resemble the pulsatility of the CSF [9]? Why do the CSF and venous pressure pulse waveforms have some characteristics of an arterial pulse [10]? Why does the intracranial pressure (ICP) pulse normally precede the arterial blood pressure (ABP) pulse, but lag with intracranial hypertension [1,6,11-14] (fig 1)? I propose that a useful approach to understanding these counterintuitive aspects of intracranial pulsatility is to consider the dynamics of the cerebral windkessel as that of a designed system. Such a system manifests design principles that accomplish specified goals, which for the cerebral windkessel is the buffering of arterial pulsatility—an unwanted ‘vibration’—in cerebral blood flow, while at the same time maintaining optimal cerebral blood flow and minimizing energy dissipation. This approach to exploring intracranial pulsatility entails reverse engineering of the cerebral windkessel, in accordance with established engineering principles of vibration control. Abstract