Increasing end-tidal CO(2) increases the estimated cerebral perfusion pressure and vice versa. These results are opposite to those expected from the known effects of CO(2) on intracranial pressure. Thus, we support the suggestion that, in the absence of intracranial hypertension, vascular tone remains a major determinant of effective downstream pressure and cerebral perfusion.

SummaryZero flow pressure is the arterial pressure at which blood flow ceases in the cerebral circulation and may represent the effective downstream pressure of this system. We used a bench model of pulsatile fluid flow to determine whether simulated changes in downstream pressure may be detected by estimation of zero flow pressure. A Doppler probe was used to record flow velocity and a pressure transducer was used to measure driving pressure. Eight different configurations of the circuit were produced, and at each configuration the external pressure around a collapsible segment of the circuit was changed in order to simulate intracranial pressure. Perfusion pressure and zero flow pressure were estimated for each configuration and each level of external pressure. The sensitivity of the model in predicting the change in external pressure from the change in zero flow pressure was 94%. This indicates that estimation of zero flow pressure by this method is a sensitive way of monitoring trends in changes in downstream pressure.

No abstract