Intracranial Pressure Waveforms are More Closely Related to Central Aortic than Radial Pressure Waveforms: Implications for Pathophysiology and Therapy.

Abstract

In patients with subarachnoid haemorrhage, pulsatile intracranial pressure (ICP) is more strongly associated with adverse events than mean ICP. Furthermore, patients with idiopathic normal-pressure hydrocephalus (iNPH), and pulsatile ICP of 5 mmHg or more, gain more benefit from cerebrospinal fluid (CSF) shunting than those whose pulsatile ICP is lower than 5 mmHg.Our study aims to investigate the morphological relationship between ICP pulsations, aortic pressure pulsations and radial artery pulsations. Central aortic pulse pressure has been known to be the best predictor of adverse cardiac events, whereas radial artery pulse pressure is generally measured and displayed in intensive care environments.We studied 10 patients with iNPH, and their ICP and aortic and radial pressures were digitised, ensemble-averaged and compared in the time and frequency domains. The ICP wave contour was quite different to the radial pressure waveform. By contrast, the ICP waveform was similar to the aortic pressure wave contour. The ICP amplitude averaged <10 % of aortic pulse pressure. In the frequency domain, the relative amplitude of the first three harmonics was similar for the ICP and aortic pressure. Hence, monitoring central aortic pressure through derivation from the radial pressure wave is superior to measurement of radial pressure alone.