title: Brain eigenfrequency shifting as a sensitive index of cerebral compliance in an experimental model of epidural hematoma in the rabbit: preliminary study.
abstract: OBJECTIVE
  To verify brain eigenfrequency shifting after the occurrence of a lesion producing mass effect into the cranial vault.
  
  
  METHODS
  Experimental animal study.
  
  
  METHODS
  Laboratory of experimental surgery affiliated with a university critical care department.
  
  
  METHODS
  Six adult male New Zealand white rabbits.
  
  
  METHODS
  A Camino ICP monitor was placed in the parenchyma, and a 5-Fr balloon-tipped catheter and accelerometer were placed into the epidural space.
  
  
  METHODS
  Before and after the introduction of successive 0.1-mL increments of autologous blood into the balloon, intracranial pressure (ICP) was recorded along with the accelerometer signal obtained during free vibration of the skull triggered by a calibrated hammer. Fast Fourier transformation of the digitized signal provided the eigenfrequency spectrum. The eigenfrequency showing the sharpest decrease after the initial 0.1-mL volume addition was considered as the best frequency, and its variation in response to subsequent 0.1-mL increments represents the brain eigenfrequency shifting.
  
  
  RESULTS
  Brain eigenfrequency shifting to lower values occurs for small blood volume increments (up to 0.2 mL). When volume addition becomes >0.3 mL, brain eigenfrequency shifting to higher values is exhibited. The decrease in best frequency after the initial introduction of 0.1 mL is statistically significant (p = .003), in a range of volume in which no significant intracranial pressure difference appears. The respective variation of ICP is explained using a quadratic curve. For volumes of 0 to 0.1 mL, the change in ICP is not statistically significant (p = .08).
  
  
  CONCLUSIONS
  Changes of the brain's physical characteristics by mass addition in the cranial vault can be expressed by brain eigenfrequency shifting. The method seems advantageous because it reliably detects mass additions at low levels where no ICP change occurs. Additionally, it provides serial measurements, and it is less invasive than the currently used methods for intracranial compliance.
authors.affiliation: Department of Critical Care, Evangelismos Hospital, University of Athens, Medical School, Greece.
authors.forename: E E
authors.initials: EE
authors.lastname: Douzinas
authors.forename: V
authors.initials: V
authors.lastname: Kostopoulos
authors.forename: E
authors.initials: E
authors.lastname: Kypriades
authors.forename: Y Z
authors.initials: YZ
authors.lastname: Pappas
authors.forename: A
authors.initials: A
authors.lastname: Lymberis
authors.forename: D I
authors.initials: DI
authors.lastname: Karmpaliotis
authors.forename: K
authors.initials: K
authors.lastname: Katsouyanni
authors.forename: I
authors.initials: I
authors.lastname: Andrianakis
authors.forename: A
authors.initials: A
authors.lastname: Papalois
authors.forename: C
authors.initials: C
authors.lastname: Roussos
mesh_terms: D000818:Animals; D015982:Bias; D001810:Blood Volume; D003187:Compliance; D004195:Disease Models, Animal; D005163:Factor Analysis, Statistical; D005583:Fourier Analysis; D006407:Hematoma, Epidural, Cranial / Q000503:physiopathology*; D007427:Intracranial Pressure; D008297:Male; D008991:Monitoring, Physiologic / Q000379:methods*; D011817:Rabbits; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted; D014732:Vibration