Correlations among intracranial pulsatility, intracranial hemodynamics, and transcranial Doppler wave form: literature review and hypothesis for future studies.

In the present work, the major correlations among cerebrospinal fluid (CSF) pulsatility, cerebral hemodynamic changes, the action of mechanisms regulating cerebral blood flow and cerebral blood volume, and the main aspects of the intracranial basal artery transcranial Doppler wave form are critically examined. CSF pulsatility is a consequence of rigidity of the craniospinal compartment and the pulsating changes in cerebral blood volume. At low and medium intracranial pressures (ICPs), changes in CSF pulsatility are mainly the result of changes in craniospinal elastance. During severe intracranial hypertension, however, CSF pulse pressure reflects an abrupt increase in cerebrovascular (i.e., cerebral vessel) compliance. The mechanisms controlling cerebral blood flow and cerebral blood volume affect CSF pulsatility through both an alteration in craniospinal blood volume and a change in vascular wall pulsatility. Examination of the main parameters of the Doppler velocity pattern (maximal systolic blood velocity, diastolic blood velocity, and peak to peak pulsatility index) in cerebral basal arteries reveals a significant alteration in the velocity wave form during severe ICP increase (above 60 mm Hg). During moderate ICP increase, when cerebral regulatory mechanisms are effective, the Doppler velocity pattern is not significantly affected by ICP changes.