CONTRIBUTION OF MATHEMATICAL-MODELING TO THE INTERPRETATION OF BEDSIDE TESTS OF CEREBROVASCULAR AUTOREGULATION

Objectives-Cerebral haemodynamic responses to short and longlasting ep isodes of decreased cerebral perfusion pressure contain information ab out the state of autoregulation of cerebral blood flow. Mathematical s imulation may help to elucidate which of the indices, that can be deri ved using transcranial Doppler ultrasonography and trends of intracran ial pressure and blood pressure, are useful in clinical tests of autor egulatory reserve. Methods-Time dependent interactions between pressur e, flow, and volume of cerebral blood and CSF were modelled using a se t of non-linear differential equations. The model simulates changes in arterial blood inflow and storage, arteriolar and capillary blood flo w controlled by cerebral autoregulation, venous blood storage and veno us outflow modulated by changes in ICP, and CSF storage and reabsorpti on. The model was used to simulate patterns of blood flow during eithe r short or longlasting decreases in cerebral perfusion pressure. These simulations can be considered as clinically equivalent to a short com pression of the common carotid artery, systemic hypotension, and inh a cranial hypertension. Simulations were performed in autoregulating and non-autoregulating systems and compared with recordings obtained in p atients. Results-After brief compression of the common carotid artery, a subsequent transient hyperaemia can be interpreted as evidence of i ntact autoregulation. During longlasting sustained hypoperfusion, a gr adual increase in the systolic value of the blood flow velocity wavefo rm along with a decrease in the diastolic value is specific for an aut oregulating cerebrovascular system. Conclusion-Modelling studies help to interpret both clinical and experimental cerebral haemodynamic phen omena and their dependence on the state of autoregulation.