Principles of cerebral hemodynamics when intracranial pressure is raised: lessons from the peripheral circulation
Kim, Mi Ok
O’Rourke, Michael F
Avolio, Alberto P
Journal of Hypertension
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Kim, M. O., Adji, A., O’Rourke, M. F., Avolio, A. P., Smielewski, P., Pickard, J., & Czosnyka, M. (2015). Principles of cerebral hemodynamics when intracranial pressure is raised: lessons from the peripheral circulation. Journal of Hypertension, 33 1233-1241. https://doi.org/10.1097/HJH.0000000000000539
Background: The brain is highly vascular and richly perfused, and dependent on continuous flow for normal function. Although confined within the skull, pressure within the brain is usually less than 15 mmHg, and shows small pulsations related to arterial pulse under normal circumstances. Pulsatile arterial hemodynamics in the brain have been studied before, but are still inadequately understood, especially during changes of intracranial pressure (ICP) after head injury. Method: In seeking cohesive explanations, we measured ICP and radial artery pressure (RAP) invasively with high-fidelity manometer systems, together with middle cerebral artery flow velocity (MCAFV) (transcranial Doppler) and central aortic pressure (CAP) generated from RAP, using a generalized transfer function technique, in eight young unconscious, ventilated adults following closed head trauma. We focused on vascular effects of spontaneous rises of ICP ('plateau waves'). Results: A rise in mean ICP from 29 to 53 mmHg caused no consistent change in pressure outside the cranium, or in heart rate, but ICP pulsations increased in amplitude from 8 to 20 mmHg, and ICP waveform came to resemble that in the aorta. Cerebral perfusion pressure (=central aortic pressure - ICP), which equates with transmural pressure, fell from 61 to 36 mmHg. Mean MCAFV fell from 53 to 40 cm/s, whereas pulsatile MCAFV increased from 77 to 98 cm/s. These significant changes (all P < 0.01) may be explained using the Monro-Kellie doctrine, because of compression of the brain, as occurs in a limb when external pressure is applied. Conclusion: The findings emphasize importance of reducing ICP, when raised, and on the additional benefits of reducing wave reflection from the lower body.
aortic pressure, intracranial pressure, plateau waves
This study was supported by the National Institute of Health Research, the Biomedical Research Centre (Neuroscience Theme), and the Medical Research Council (Grants G0600986 and G9439390). J.D.P. has received the NIHR Investigator Awards. M.O.K. is sponsored by an Australian Postgraduate Awards Industrial Linkage Grant from the Australian Research Council (LP0884094), with AtCor Medical Australia as the collaborating organization.
External DOI: https://doi.org/10.1097/HJH.0000000000000539
This record's URL: https://www.repository.cam.ac.uk/handle/1810/247532