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Cerebral autoregulation

The brain relies on a continuous and adequate supply of blood flow, bringing the nutrients that it needs and removing the waste products of metabolism. It is thus one of the most tightly regulated systems in the body, whereby a whole range of mechanisms act to maintain this supply, despite changes in blood pressure etc. Failure of these mechanisms is found in a number of cerebral diseases, including stroke, vascular dementia and brain injury and trauma.

One of the other difficulties in interpreting measurements made from the brain is that there are so many different factors affecting any measurement (for example, blood pressure, blood gas levels, neural activity). Trying to disentangle all of these requires very advanced signal processing as well as physiological models. This is particularly important in interpreting data from patients, where the assumptions that are normally made are much less likely to be valid. For example, how the regulation of blood flow is affected in stroke is still very poorly understood, so this links directly to our work on stroke.

We are also developing more theoretical models of the control of flow of blood through vessels. Blood is a non-Newtonian fluid with a pulsatile flow in flexible walls: there is both mechanical coupling though the wall's viscoelastic nature and chemical coupling through the transport of substances such as Nitric Oxide (which plays a vital role in regulation). Solving the equations and understanding the nature of this coupling, particularly in disease, is extremely hard. There are various models that we are developing, from single vessels (both looking at autoregulation at a local level and vasomotion) to models of the whole cerebral vasculature. One key part of this modelling is to investigate whether we can predict markers of brain disease, that could be used clinically: one example is vasomotion, which is thought to occur only when blood flow drops as an important part of the brain's response to reduced perfusion. We are investigating both how this affects oxygen transport to tissue and why it occurs at reduced flow levels with a view to understanding its role in the brain, as well as seeing whether we can detect the oscillations in clinically available measurements.

We are closely involved with the Cerebral Autoregulation Research Network (CARNet), which is leading the way to improve collaboration in this area.