Physics Offers New Techniques to Analyse Blood Flow
New research carried out in Lancaster University's Physics department has shown that measuring the frequencies in blood flow in a patient could help to diagnose disease. Peter McClintock, professor of physics at Lancaster University is supported by an EPSRC 'Physics for Healthcare' award to investigate variations the cardiovascular system.
He explained: 'The heart does not beat regularly, but varies in a complicated way. The whole cardiovascular system - the heart, lungs, arteries, veins and peripheral system interacts to create a non linear dynamical system with subtle behaviours.This can tell us about the state of a patient's health.'
The research is in collaboration with Dmitri Luchinsky at Lancaster, Aneta Stefanovska at the University of Ljubjana, Slovenia and researchers Natalia Janson and Alexander Balanov from Saratov State University in Russia.
The researchers make several different measurements simultaneously on a resting person over about half an hour. Heart rate, blood pressure and respiration are recorded and the average blood flow velocity is determined from a signal from a low-power infrared laser shining on the arm.
Professor McClintock said: 'It seems that there are at least five different frequencies in blood-flow dynamics. In addition to heart beat and respiration, there are also three lower frequencies that seem to be associated respectively with myogenic activity of smooth muscle cells, metabolic processes and endothelial function (the endothelium being a layer of cells on the insides of blood vessels).'
Although people have know about some of these lower frequencies for several years it was not possible to study them in any detail using standard methods. By applying the more recently developed method called wavelet transform, Professor Stefanovska was able to show that there are five frequencies, and that they are detectable for all types of measurement. It appears that the different frequencies are not independent: each is either modulated by the next lower one, or synchronises with it.
The absence or presence of synchronisation indicates the strength of the coupling and, the stronger the coupling, the higher the probability of locking. The Lancaster group has developed a new theoretical approach based on nonlinear dynamics enabling synchronisation between pairs of processes to be inferred from a single signal. It has been successfully applied to cardiac signals. This tells us about someone's health. 'We expect the strengths of the couplings will be related to the physiological condition.' says Professor McClintock. 'In athletes the couplings are stronger than average. In a patient close to death Professor Stefanovska found that the couplings had practically disappeared, showing that the system had ceased to function as an integral unit.'
In collaboration with consultant cardiologist Peter Clarkson at the Royal Lancaster Infirmary, Professor McClintock plans to observe patients with congestive heart disease. In the long term they hope to develop a useful inexpensive tool for early diagnosis and for assessing treatment. It may also be possible to apply the approach to other diseases, such as diabetes, and to develop a new method of measuring depth of anaesthesia.