ABSTRACT
The aim of the present work is to develop a non-destructive, non-invasive technique for the early diagnosis of an oncoming brain edema based on the variation of vibration characteristics of the head system (i.e. eigenfrequency spectrum and modal damping). Besides the theoretical model that supports the basic principle, the proposed technique has been verified experimentally in animal tests. The advantage of such an approach is that the relative information is available well in advance an increase of intracranial pressure is detected. The uncontrolled intracranial hypertension is associated with increased mortality or vegetative state in head trauma. Traumatic lesions located on temporal lobe render particularly impeding the transtendorial herniation. From the medical point of view, intracranial pressure (ICP) monitoring represents an effective way for early consideration of neurological decompensation in various neurosurgical conditions particularly in the head-injured setting. However, the use of ICP monitoring is not an effective way of brain edema detection, since ICP increase very often causes irreversible problems to the patient's brain. Therefore, the determination of an earlier, less invasive and more sensitive indicator of the oncoming intracranial hypertension and of the impeding neurological deterioration is of profound importance. The present work aims at experimental verification of both eigenfrequency shifting and modal damping increase of the spectral response of the head system of rabbits, wherever a mass increase in the content of cranial shell appears. The conducted analysis concludes that the eigenfrequency spectrum and its modal damping characteristics are sufficiently sensitive parameters in order to characterize mass increase in the cranial shell. Therefore the combination of both the above parameters could be used with confidence for the early diagnosis of brain edema.
Subject(s)
Brain Edema/diagnosis , Intracranial Hypertension/diagnosis , Intracranial Pressure , Models, Cardiovascular , Monitoring, Physiologic , Temporal Lobe/injuries , Animals , Blood Pressure Determination/instrumentation , Blood Pressure Determination/methods , Brain Edema/mortality , Disease Models, Animal , Humans , Intracranial Hypertension/mortality , Male , Monitoring, Physiologic/instrumentation , Monitoring, Physiologic/methods , Rabbits , Reproducibility of ResultsABSTRACT
OBJECTIVE: To verify brain eigenfrequency shifting after the occurrence of a lesion producing mass effect into the cranial vault. DESIGN: Experimental animal study. SETTING: Laboratory of experimental surgery affiliated with a university critical care department. SUBJECTS: Six adult male New Zealand white rabbits. INTERVENTIONS: A Camino ICP monitor was placed in the parenchyma, and a 5-Fr balloon-tipped catheter and accelerometer were placed into the epidural space. MEASUREMENTS: 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. MAIN 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.
