Non-invasive monitoring of the intracranial pressure waveform

Abstract

Invasive monitoring of intracranial pressure (ICP) plays an essential role in diagnostics and surveillance of patients with brain injury and brain disease. While monitoring of mean ICP is a cornerstone of cerebrovascular monitoring worldwide, an increasing body of research highlights the added clinical benefit of also considering the cardiac-induced pressure variations in the ICP signal, namely the pulsatile ICP. Numerous studies have shown that patient management based on the Mean Wave Amplitude (MWA) of the pulsatile ICP has improved the outcome for patients with different pathologies compared to mean ICP patient management alone. Current measurement modalities of mean and pulsatile ICP are all invasive with associated risks of intracranial bleeds and infections. The primary aim of the research upon which this thesis is based was, therefore, to estimate the MWA parameter non-invasively in order to safely provide the clinicians with added information about the intracranial condition. Non-invasive MWA estimation has been performed in two different studies using two different physiological time-series as input. The first study utilizes the central aortic blood pressure waveforms and a statistical model to estimate pulsatile ICP. The second study uses the same methodology, but the pressure oscillations measured in the outer ear are used as the input signal. The studies both gave reasonably good visual estimates of the ICP morphology, but not to the extent where the MWA parameter could be extracted with the necessary clinical confidence. The latter study also revealed that the cochlear aqueduct is dispersive for high frequencies and therefore can only be expected to reproduce the lowest frequency components of the ICP morphology well. The majority of patients studied for this thesis suffer from iNPH, which is a neurodegenerative dementia illness combined with CSF circulatory failure, that is currently not sufficiently understood. To shed light on this disorder, the MWA parameter’s dependence on hemodynamic events was explored in a third study, revealing that the consistently elevated MWA that is reported in iNPH patients is due to intracranial conditions, not cardiovascular events.