Cerebral Hemodynamics through Intracranial Pressure

Traumatic Brain Injury (TBI) continues to be a major problem worldwide. Today, intensive care of patients with TBI is mainly focused on preventing and treating secondary brain injuries. High pressure inside the intracranial cavity has been found to be an important feature of disturbed cerebral dynamics and secondary injuries. Thus, invasive measurement of intracranial pressure (ICP) is today a well established routine in modern neuro-intensive care. Variations in ICP can be regarded as a response of the cerebrospinal system to different stimuli, including homeostatic mechanisms which attempt to maintain the cerebral equilibrium. Nevertheless, the autoregulatory processes and their functionality may also be affected by ICP. This study is an attempt to investigate the cerebral hemodynamics through analysis of ICP and other biomedical measurements available, such as arterial blood pressure and electrocardiography. The study is mainly conducted by analysing biomedical data through mathematical modelling, model-based frameworks, and simulations. This thesis focuses on the dynamics of intracranial pressure in either presence or absence of cerebral autoregulation. A model-based framework which describes the relationship between arterial distensibility and compliance was developed to study variations in the mechanical properties of distant cerebral artries/arteriols. The measurements of pulse wave propagation velocity as well as transfer function between arterial blood pressure and intracranial pressure were utilized as the key elements of the study. Using the aforementioned model, it was shown that variations in the level of ICP may arise from different states of cerebral autoregulation and the associated regime within the cerebral vasculature. The state of Cerebral Blood Flow (CBF) autoregulation during plateau waves of ICP was taken as a subsequent focus of the study. The investigation was conducted by applying the mathematical models of cerebral hemodynamics to the measurements from a TBI patient. Considering the mechanical properties of the cerebrovascular system, the study examined models of impaired as well as intact CBF autoregulation as the possible options. Although the intact autoregulatory mechanism could simulate elevated ICP waves, a large time constant of regulation far from the reported response