Relazione tra doppler transcranico e dinamica intracranica in corso di lesioni acute cerebrali

The use of Transcranial Doppler for monitoring of patients with acute brain damage requires a wide knowledge of the relationships among cerebral hemodynamics, systemic arterial pressure, intracranial pressure and cerebral perfusion pressure. Aim of this work is to clarify the clinical meaning of the main parameters obtained from the Transcranial Doppler (systolic velocity, diastolic velocity, mean velocity pulsatility index) under conditions characterized by acute alterations of intracranial dynamics. The analysis has been performed using an original mathematical model of cerebrospinal fluid and cerebrovascular dynamics. The model suggests that alterations in the Transcranial Doppler waveform and in pulsatility index are the product of the complex interactions among autoregulation, cerebrospinal fluid dynamics, intracranial compliance and vascular compliance. Particulary, the present results show that, in conditions of impaired intracranial dynamics, alterations in the Transcranial Doppler parameters and pulsatility index are not alwais an expression of cerebrovascular resistance, but rather may be caused by a reduction in cerebral perfusion pressure toward the lower autoregulation limit.