Cerebral autoregulation measurement
Our neurological physics team are part of a collaboration of researchers in Southampton who are developing methods for non-invasive assessment of cerebral autoregulation. Find out more about what cerebral autoregulation is and why it is so important on the Cerebral Autoregulation Research Network website.
- We were the first group to describe the widely used phase relationship between blood pressure and cerebral flow velocity (Stroke vol 26, 1995 pp. 834-837).
- We introduced periodic lower body negative pressure as a stimulus providing one of the most repeatable measures of cerebral autoregulation (Physiological Measurement 23 (1) 2002 pp. 73-83).
- We identified non-invasive measurements of blood pressure as one of the primary sources of error in dynamic cerebral autoregulation measurements (Physiological Measurement 24 (3) 2003 pp. 653-661).
- We have described novel theoretical modelling of cerebral autoregulation dynamic measurements (Mathematical and Computer Modelling of Dynamical Systems 9 (4) 2003 pp. 367-386).
Figure 1: Measuring the phase relationship between blood pressure and cerebral flow velocity.
Our recent work
New methods for assessing the control of blood flow in the brain
This collaboration between ourselves and the universities of Southampton, Leicester and East Anglia was funded by the EPSRC: EP/E029221/1. The main aims were to:
- Explore a number of new and innovative experimental protocols that exploit pseudo-random binary sequences in provoking repeated but relatively small variations in arterial blood pressure (ABP) and arterial carbon dioxide levels (pCO2), from which the active control of cerebral blood flow can be measured.
- Develop and evaluate a range of advanced signal analysis procedures, that allow the dynamic interaction between cerebral blood flow velocity (CBFV), ABP and pCO2 to be quantified, using innovative approaches in multivariate linear and nonlinear system identification, as well as adaptive methods.
- Based on a critical comparison of results from all the different techniques and protocols investigated in this joint project, recommend sensitive and robust procedures for the non-invasive measurement of the blood flow control system in vulnerable patients.
- Increase the understanding of the dynamic interaction between CBFV, ABP and pCO2, based on modelling of experimental data.
This project has now been completed.
The assessment of cerebral autoregulation using MRI
Find out about this work on our MRI physics: research and development page.
Our current work
Diversity in blood flow control to the brain: moving from individualised modelling towards personalized treatment of the injured brain
This three year project is funded by EPSRC (UK) with linked studies in Southampton (David Simpson, Tony Birch, Diederik Bulters), Oxford (Stephen Payne) and Leicester (Tom Robinson, Ronney Panerai). The project sets out in a new direction for the field, by focusing on the diversity of ways in which brain blood flow may operate in different individuals, rather than studying average group behaviour, which has so far been the predominant approach. It also breaks new ground methodologically by integrating the study of blood flow control with that of blood pressure control, based on the complementary roles these have in ensuring that the brain receives sufficient blood. We will investigate a sample of healthy volunteers in detail. We will repeatedly record blood pressure and flow, heart rate and carbon dioxide levels during spontaneous fluctuations at rest, and during challenges in a range of protocols (periodic squatting, raising the upper body, applying random pressure changes to a cuff around the thighs, breathing air with 5% CO2). Using advanced data analysis methods (signal processing and mathematical modelling), some of which will be developed and optimised as part of this project, we will quantify the simultaneous control of blood pressure and flow and aim to identify characteristic differences between individuals and sub-groups.
Building on the differences observed in the healthy subjects, we will also study a group of patients during the first days and weeks after they have suffered a stroke. We aim to quantify the impairments in blood flow and blood pressure control, with a view to improving understanding of the evolution of this condition, and how this might impact the management of their blood pressure in the acute and chronic phase. Correct functioning of these control systems is thought to be key in making effective clinical decisions, but currently there are no clear guidelines due to a lack of understanding of the impairments in each individual patient and also the methods for their measurement.
The overarching aim of this multicentre and multidisciplinary project is to lay the foundations for a personalised approach to managing blood pressure control after stroke, based on characterising individuals' blood pressure and flow control, protecting patients' brains from further damage.
Meet the team
Dr Tony Birch is head of neurological physics and leads our research into cerebral autoregulation measurement.
Medical physics department
Southampton General Hospital