title: Resonant and notch behavior in intracranial pressure dynamics.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Radiology, Stony Brook University, Stony Brook, New York 11794, USA. mark.wagshul@stonybrook.edu
authors.forename: Mark E
authors.initials: ME
authors.lastname: Wagshul
authors.forename: Erin J
authors.initials: EJ
authors.lastname: Kelly
authors.forename: Hui Jing
authors.initials: HJ
authors.lastname: Yu
authors.forename: Barbara
authors.initials: B
authors.lastname: Garlick
authors.forename: Tom
authors.initials: T
authors.lastname: Zimmerman
authors.forename: Michael R
authors.initials: MR
authors.lastname: Egnor
mesh_terms: D000818:Animals; D001794:Blood Pressure / Q000502:physiology*; D002555:Cerebrospinal Fluid / Q000502:physiology*; D004285:Dogs; D006339:Heart Rate / Q000502:physiology*; D007427:Intracranial Pressure / Q000502:physiology*; D008991:Monitoring, Physiologic; D011674:Pulse; D013057:Spectrum Analysis