Understanding the Impact of Large Vessel Occlusion on Brain Tissue Pulsatility

Background: It has long been known that the brain pulsates in synchrony with the cardiac cycle. However, the underlying generation of these brain tissue pulsations (BTPs) has yet to be fully modelled and clinical measurement of BTPs remains relatively unexplored.

Aims: This thesis aimed to employ a novel ultrasound technique, known as transcranial tissue Doppler ultrasound (TCTD), to investigate if BTPs are disturbed in the presence of stroke, including large vessel occlusion (LVO). Additionally, it aimed to examine the impact of elevated intracranial pressure (ICP) on BTPs and investigate the impact of blood pressure (BP) on BTPs.

Methods: A scoping review identified emerging LVO detection techniques. A clinical feasibility study with 100 suspected stroke patients was conducted to collect BTP data. An ultrasound brain phantom model simulated LVO by occluding the internal carotid artery (ICA) and examined the effects of raised ICP on BTPs. A pilot study involving healthy volunteers assessed the impact of the Valsalva manoeuvre (VM) on BTPs. A further phantom experiment investigated the impact of blood pressure (BP) on BTPs.

Results: BTPs appear disturbed in stroke in both stroke patients and in a phantom model, but changes were small and not statistically significant. The results of the healthy volunteer study and a phantom study identified that elevated ICP constrains brain motion. Bulk BTP amplitude was found to mirror changes in pulse pressure (PP).

Conclusion: This thesis introduces TCTD as a potentially viable technique for real-time measurement of BTPs in stroke patients, which may enhance clinical stroke assessment. This thesis also found that BTPs appear disturbed in acute ischaemic stroke (AIS), are constrained in elevated ICP, and are strongly influenced by pulse pressure (PP). Further work should aim to clarify the relationship between BTPs and cerebrovascular physiology, including cerebral blood velocity (CBv) and ICP.