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Ursino, M., A. Ter Minassian, C. A. Lodi, and L. Beydon. Cerebral hemodynamics during arterial and C[O.sub.2] pressure changes: in vivo prediction by a mathematical model. Am J Physiol Heart Circ Physiol 279: H2439-H2455, 2000.--The aim of this work was to analyze changes in cerebral hemodynamics and intracranial pressure (ICP) evoked by mean systemic arterial pressure (SAP) and arterial C[O.sub.2] pressure [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] challenges in patients with acute brain damage. The study was performed by means of a new simple mathematical model of intracranial hemodynamics, particularly aimed at routine clinical investigation. The model was validated by comparing its results with data from transcranial Doppler velocity in the middle cerebral artery ([V.sub.MCA]) and ICP measured in 44 tracings on 13 different patients during mean SAP and [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] challenges. The validation consisted of individual identification of 6 parameters in all 44 tracings by means of a best fitting algorithm. The parameters chosen for the identification summarize the main aspects of intracranial dynamics, i.e., cerebrospinal fluid circulation, intracranial elastance, and cerebrovascular control. The results suggest that the model is able to reproduce the measured time patterns of [V.sub.MCA] and ICP in all 44 tracings by using values for the parameters that lie within the ranges reported in the pathophysiological literature. The meaning of parameter estimates is discussed, and comments on the main virtues and limitations of the present approach are offered. carbon dioxide reactivity; intracranial pressure; cerebral autoregulation; severe brain damage; transcranial Doppler

Presents information on a study which investigated the changes in cerebral hemodynamics and intracranial pressure evoked by mean system arterial pressure and arterial carbon dioxide pressure challenges in patients with acute brain damage. Methodology of the study; Results and discussion on the study.

The mathematical model presented in a previous work is used to simulate the time pattern of intracranial pressure (ICP) and of blood velocity in the middle cerebral artery (VMCA) in response to maneuvers simultaneously affecting mean systemic arterial pressure (SAP) and end-tidal CO2 pressure. In the first stage of this study, a sensitivity analysis was performed to clarify the role of some important model parameters [cerebrospinal fluid (CSF) outflow resistance, intracranial elastance coefficient, autoregulation gain, and the position of the regulation curve] during CO2 alteration maneuvers performed at different SAP levels. The results suggest that the dynamic "ICP-VMCA" relationship obtained during changes in CO2 pressure may contain important information on the main factors affecting intracranial dynamics. In the second stage, the model was applied to the reproduction of real ICP and velocity tracings in neurosurgical patients. Ten distinct tracings, taken from six patients during CO2 changes at different mean SAP levels, were reproduced. Best fitting between model and clinical curves was achieved by minimizing a least-squares criterion function and adjusting certain parameters that characterize CSF circulation, intracranial compliance, and the strength of the regulation mechanisms. A satisfactory reproduction was achieved in all cases, with parameter numerical values in the ranges reported in clinical literature. It is concluded that the model may be used to give reliable estimations of the main factors affecting intracranial dynamics in individual patients, starting from routine measurements performed in neurosurgical intensive care units.