Vascular regulation

Blood pressure is necessary to provide blood flow around the body. It is a very dynamic parameter varying from second to second and from one part of the body to another. When we stand the pressure in our feet increases and the pressure to our heads reduces. We might expect blood flow to change as blood pressure changes but there exists a regulation mechanism to prevent this from happening. When blood pressure increase small arteries constrict to prevent an increase in flow and similarly when blood pressure drops then the arteries dilate to prevent any reduction in flow.

This mechanism is also able to meet demands for changes in blood flow; blood flow can vary hugely in some organs, for example the skin blood flow will increase dramatically in hot weather to behave as a temperature regulator, and muscle blood flow will increase hugely during exercise. Regulation of blood flow to some organs, particularly the brain and the heart is more crucial than others. The physiological mechanisms that make up this autoregulatory control system are extremely complex and not fully understood.

In some people this vascular regulation may fail or reach its limit. In the early stages of disease the regulatory performance may be impaired without producing any outward symptoms. Blood flow regulation processes in the body are crucial to our survival yet rarely assessed in clinical practice. This is because the system is so complex that the measurements are difficult to interpret. 

The broad focus of this project area is the development of new methods to assess vascular regulation. Our primary interest is regulation of blood flow to the brain but we are interested in regulation of the whole circulatory system.

Broad research goals of the neurological physics group in this area:

• Develop new methods to assess vascular regulation.
• Assess clinical applications for specific techniques.
• Improve understanding of vascular physiology and pathology.

Description and rationale of approach being taken

The approach taken to assess cerebral autoregulation has been to vary blood pressure while measuring flow. This has been attempted by many groups but is fraught with complications. Our approach is to apply a periodic blood pressure variation. We have shown that the average phase relationship between pressure and flow is a good index of cerebral autoregulation. The measurements are very promising but are too uncomfortable to be practical for the original purpose. Our future direction is to build upon this technique, improving the practicalities of the measurement and extending the application to other parts of the body.

Achievements to-date

• First group to describe the widely used phase relationship between blood pressure and cerebral flow velocity. Stroke. 1995;26:834-837. 
• Introduced periodic lower body negative pressure as a stimulus for one of the most repeatable measures of cerebral autoregulation. Physiological Measurement 23 (1), 2002, 73- 83.
• Identified non-invasive measurements of blood pressure as one of the primary sources of error in dynamic cerebral autoregulation measurements. Physiological Measurement Vol 24 Number 3 2003 pp 653-661.
• Described novel theoretical modelling of cerebral autoregulation dynamic measurements. Mathematical and Computer Modelling of Dynamical Systems Vol 9; Number 4 2003 pp. 367-386.

If you would like more information or would like to contribute to this project please contact Tony Birch by email Tony.birch@suht.swest.nhs.uk| or telephone 023 80796335.