Background: Traditional models of intracranial dynamics fail to capture several important features of the cerebral windkessel. Experiments show that the cerebral windkessel is a band-stop filter tuned to the heart rate, which is not consistent with existing pressure-volume compartment models. Flow MRI studies in humans reveal expansion and relaxation of the cranial contents during the cardiac cycle that continuously opposes arterial expansion and relaxation, and we suggest this is the way the windkessel is implemented in the cranium. This systolic-diastolic brain motion is analogous to the loading and unloading of the capacitor plates in the model circuit.
Methods: In this study, we use exogenous input autoregressive (ARX) modeling of a simple band-stop electrical circuit to model the cerebral windkessel of normal dogs. We compare the circuit waveforms to waveforms measured in dogs, and we examine the dynamics that underlie the cerebral windkessel.
Results: Our ARX analysis shows close agreement between the circuit and the windkessel, which implies similar physical mechanisms of pulsation suppression. This correspondence between physiological data and circuit dynamics suggests that the cerebral windkessel is a frequency-sensitive band-stop filter for the passage of arterial power through the cranium. Another perspective from which to understand the windkessel is to consider the smooth offset and the pulsatile components of cerebral arterial flow as DC and AC power respectively. In the cranium, DC power of cerebral blood flow passes through the capillary bed to the veins and AC power is diverted through the CSF to the veins. This windkessel mechanism optimizes smooth capillary flow and minimizes potentially damaging capillary pulsatility.
Conclusions: Our windkessel model provides substantial new insights into intracranial dynamics, cerebral blood flow and capillary circulation, and it provides a new framework for the study and treatment of several common disorders of intracranial dynamics such as cerebral edema, hydrocephalus, pseudotumor cerebri, and Cushing’s reflex.