Resonant and notch behavior in intracranial pressure dynamics

Abstract

<jats:sec> <jats:title>Object</jats:title> <jats:p>The intracranial pulse pressure is often increased when neuropathology is present, particularly in cases of increased intracranial pressure (ICP) such as occurs in hydrocephalus. This pulse pressure is assumed to originate from arterial blood pressure oscillations entering the cranium; the fact that there is a coupling between the arterial blood pressure and the ICP is undisputed. In this study, the nature of this coupling and how it changes under conditions of increased ICP are investigated.</jats:p></jats:sec> <jats:sec> <jats:title>Methods</jats:title> <jats:p>In 12 normal dogs, intracarotid and parenchymal pulse pressure were measured and their coupling was characterized using amplitude and phase transfer function analysis. Mean intracranial ICP was manipulated via infusions of isotonic saline into the spinal subarachnoid space, and changes in transfer function were monitored.</jats:p></jats:sec> <jats:sec> <jats:title>Results</jats:title> <jats:p>Under normal conditions, the ICP wave led the arterial wave, and there was a minimum in the pulse pressure amplitude near the frequency of the heart rate. Under conditions of decreased intracranial compliance, the ICP wave began to lag behind the arterial wave and increased significantly in amplitude. Most interestingly, in many animals the pulse pressure exhibited a minimum in amplitude at a mean pressure that coincided with the transition from a leading to lagging ICP wave.</jats:p></jats:sec> <jats:sec> <jats:title>Conclusions</jats:title> <jats:p>This transfer function behavior is characteristic of a resonant notch system. This may represent a component of the intracranial Windkessel mechanism, which protects the microvasculature from arterial pulsatility. The impairment of this resonant notch system may play a role in the altered pulse pressure in conditions such as hydrocephalus and traumatic brain swelling. New models of intracranial dynamics are needed for understanding the frequency-sensitive behavior elucidated in these studies and could open a path for development of new therapies that are geared toward addressing the pulsation dysfunction in pathological conditions, such as hydrocephalus and traumatic brain injury, affecting ICP and flow dynamics.</jats:p></jats:sec>

Effect of infusion tests on the dynamical properties of intracranial pressure in hydrocephalus

“…ICP oscillates during the cardiac cycle as a result of cardiac-driven variations in ABP [42]. The blood volume entering the brain changes within the cardiac cycle, resulting in a net intracranial inflow of blood during systole and net outflow during diastole [41].…”

“…These blood volume changes during the cardiac cycle must be compensated by the CSF volume changes in order to maintain a stable ICP, leading to ABPdriven pulsations in CSF pressure [41]. However, vascular compliance seems to be reduced in disorders such as NPH [42]. Besides, it has been suggested that volume load during ITs may also have a relevant impact in the compliance of the brain and cerebral blood vessels.…”

Function of Circle of Willis

“…Modulation of absorption of energy inputted into the system is complex and dependent on cardiac frequency. 31,58,59 FUNCTION OF THE CIRCLE OF WILLIS-HYPOTHESIS We hypothesize that CW functions as a pressure absorber mechanism that prevents damage of the cranial microvasculature and BBB.…”

Spectral analysis of intracranial pressure signals recorded during infusion studies in patients with hydrocephalus

“…Vascular compliance is important in the brain because it is surrounded by a rigid container (the skull) and an incompressible fluid (CSF) [41]. It is generally accepted that the oscillation of ICP with the cardiac cycle is a result of the cardiac-driven variations in ABP [42]. The volume of intracranial blood varies along one cardiac cycle, due to the pulsatile nature of the blood supply in the brain: it increases during systole and decreases during diastole [41,43].…”

“…As a consequence, the morphology of the CSF waveform suffers changes that depend on the arterial input, the compliance of the cranial contents (parenchyma and cerebral wall) and the blood flow towards the venous system [41,44]. However, the relationship between ABP and ICP oscillation appears to be altered in clinically relevant conditions such as hypertension and hydrocephalus [42].…”