Using sophisticated analysis of heart rate information, researchers at the University of Warwick have devised a way to diagnose sleep disorders that replaces the detailed and expensive medical investigations currently used.
The number of patients coming forward with sleeping disorders is increasing. Birmingham Heartlands Hospital alone dealt with over 400 sleep disorder cases in the last year. The main problem is sleep apnoea which means “stopping breathing during sleep”. This can occur up to 300 times in one night. Consequences of sleep apnoea include extreme daytime sleepiness, which can result in loss of jobs and even cause road traffic accidents. People who have sleep apnoea are more likely to suffer high blood pressure and die from heart attacks. Most sleep disorder patients can only be diagnosed after a complicated procedure known as polysomnography, for which patients are admitted to hospital overnight. Whilst asleep, they are tested by an array of instruments measuring individual leg and eye movements, electrocardiograms (ECGs), brain waves, chest movements, oxygen level in the blood, snoring and air flow through the nose and mouth.
Every time a sleep apnoea sufferer stops breathing and subsequently awakes, the heart rate is affected. However, doctors have not so far used this heart rate effect as a diagnostic tool for two reasons. Firstly, healthy hearts do not have an entirely regular heart rate, preventing detailed analysis until now. Secondly, the wide variation across patients in the intensity of sleep apnoea means that it is impossible to decide on a simple single quantitative measure to look for when examining ECGs of heart activity. Now researchers at the University of Warwick, working in a cross departmental research group applying mathematical techniques to medical problems, have devised a single analysis of the heart rate which will greatly reduce the time - consuming and expensive polysomnography procedure.
The researchers have combined their knowledge to use mathematical tools to cope with the heart's irregular rate and the wide variation in the effects of sleep apnoea on the heart rate.
They experimented with the application of two mathematical concepts - the Non-equispaced Fourier Transform, and the Discrete Harmonic Wavelet Transform - to the ECGs of 20 sleep apnoea patients and 20 normal subjects. They discovered that by using these tools they could indeed simply diagnose sleep apnoea from the ECG alone. The advantages of this new technique include:
- The ECG data can be analysed in just 20 minutes. Polysomnography data takes 4 - 6 hours.
- A patient can take a portable ECG monitor home. They do not need to be admitted to hospital.
- The technique will allow non - sleep specialist doctors looking at ECGs of patients to diagnose sleep apnoea, even if they were using the ECG to look at other conditions.
- The team are now looking at the effect of other conditions on heart rate and believe they can refine the process for application to other heart conditions, asthma and diabetes.
Dr Ron Bates, Dept of Statistics
024 76 522062 email: R.A.Bates@warwick.ac.uk