(Madrid, 13 October 1999) A medical team at the Txagorritxu Hospital in Vitoria (Spain), led by Dr Joaquín Durán, carried out a detailed study of the sleep patterns of 1050 men and 1098 women over a period of four years.
Out of this population, chosen to be representative of the 200 000 inhabitants of this Basque town in Spain, it was found that 26.2% of the men and 28% of the women stopped breathing more than five times an hour, the threshold of what is considered "abnormal" by the specialists.
The figures are equally impressive when it comes to men and women who stop breathing during their sleep twice as often, i.e. ten times an hour, since no less than 19% of men and 14% of women are affected. "We usually refer to these critical thresholds to define the obstructive sleep apnea (OSA)", says Dr Durán.
To arrive at these results, which were reported Wednesday morning at the 9th annual meeting of the European Respiratory Society (ERS) and which are applicable to Europe as a whole, the Spanish doctors followed a well tried protocol conforming to the best international standards.
The investigators first visited the participants at home to inquire whether they slept well or not. They made a night polygram on the spot, using a portable apparatus to record data ranging from oxygen saturation of the blood, to heartbeat, snoring and bodily position.
Ten-second stoppages five times an hour
The second phase of the study took place in the hospital. All individuals showing critical values in the measurements made at home, and a subsample of those with normal values, were called in to undergo a more detailed examination. In the hospital, once they were asleep, they were subjected to polysomnography tests, combining electroencephalography, electrooculography (recordings of eye movements), electromyography (recordings of muscle movements) and electrocardiography. Respiratory sensors and microphones placed on the neck to record tracheal sound were used to make accurate measurements of the time during which the person stopped inhaling.
"What we call respiratory pause is when a person stops breathing for at least ten seconds", explains Dr Durán.
When such stoppages (due in most cases to the obstruction or collapse of the tissues of the throat) occur more than five times an hour, it may lead to other disorders.
The first effect is that many OSA sufferers, who rest badly at night, experience moments of drowsiness during the day.
In the study carried out in the Basque Country, 14% of the men and 22% of the women said they felt sleepy frequently at least three days a week, both at work and off work. Clearly the consequences can sometimes be dramatic.
A survey of some hundred drivers involved in traffic accidents, published in the highly respectable New England Journal of Medecine, confirms just how dangerous OSA-induced states of drowsiness can be.
The survey concludes that persons who stop breathing more than ten times an hour during their sleep are six times more likely to cause a traffic accident than those unaffected by sleep disorders.
Potential heart problems
But the impact of OSA on health can be even more serious, as shown by studies reported at the ERS meeting. Many suggest that there is a direct link with cardiovascular diseases, although the exact causal relationship is still not known.
For instance, at the Hot Topic symposium on "Prevalence and clinical outcome of OSA" held in Madrid on Wednesday, Dr Robert Davies, lung specialist at Oxford Radcliffe Hospital (UK), reported some as yet unpublished results that point to a link between OSA and hypertension.
To obtain these results, the British doctor and his colleagues measured the blood pressure of 37 patients suffering from sleep apnea over 24 hours. They reached the conclusion that blood pressure among individuals who stop breathing over ten times an hour is systematically greater than that of a control group. Of course, the authors of the study took care to take account of other factors which might cause pressure to rise, by selecting individuals for the control group and the OSA group who were similar with regard to age, sex, weight and smoking habits.
The link between sleep apnea and cardiovascular mortality was also shown in a Swedish study presented on Tuesday morning. As they explained during their oral communication, Dr Yüksel Peker and his colleagues at Sahlgrenska University Hospital of Gothenburg spent five years following 59 patients who had suffered some form of coronary disease requiring intensive care.
By the end of the study, 38% of patients with OSA had died, compared with only 9% of the patients unaffected by apnea. The authors reported that the number of nocturnal breathing pauses was an independant risk factor for mortality.
A respiratory mask as a remedy
There is one possible therapy for dealing with the ill effects of OSA, even though it is not always ideal. It is known by the initials CPAP, for "continuous positive airway pressure".
The method consists in blowing air continuously through a mask, which is attached the whole night long to the patient's nose. The positive pressure prevents the throat from collapsing, thus abolishing obstructive apneas. Robert Davies and his colleagues found that this device had the effect of lowering blood pressure in OSA patients.
This is not the only advantage of the technique, however, since the uses of CPAP now extend beyond the field of lung diseases, as shown in Madrid. Having carried out many clinical studies of this form of respiratory aid since 1989, Dr Douglas Bradley of the University Hospital of Toronto (Canada) has found that it may help prolong the survival of patients suffering from congestive heart failure, and avoid the need for a transplant. He reported his results at the symposium on "Cardiovascular interactions in sleep-disordered breathing" at the 9th ERS meeting.
Frequently persons suffering from congestive heart failure show signs of a particularly insidious form of the disorder known as central sleep apnea, abbreviated to CSA.
Unlike OSA, the CSA type of apnea is due not to an obstruction of the throat, but to the absence of a signal from the brain to breathe. This causes breathing to cease for 10 to 60 seconds.
Dr Bradley and his colleagues recently tested the effects of CPAP in 66 patients suffering from congestive heart failure, of whom 29 were affected by CSA.
After two and a half years of trial, the rate of death and heart transplantation was reduced by 60% in patients who were treated with CPAP compared to a group receiving standard care but not CPAP. Among the patients with CSA, the beneficial effect was even more pronounced, with an 80% reduction in the rate of death and heart transplantation! "At the present time, said Douglas Bradley, this is an area that is almost completely ignored by cardiologists to the detriment of their patients".
As he indicated at the 9th ERS meeting, the Toronto team will be undertaking a more extensive study, involving over 400 heart failure patients with CSA in seven healthcare centers in Canada to see whether these encouraging initial results can be duplicated in a larger population. These new data are expected in 3 to 4 years' time.
Note to the Editor: please do not forget to mention that this study has been presented at the Madrid ERS annual meeting.
This release was written by Eric Schaerlig, Igor Chlebny and Peter Whiting, Cedos International, 1227 Carouge-Geneva
Contacts:
Dr Joaquín Durán
Hospital de Txagorritxu, Vitoria (Spain)
Phone: +34 9 45 007007
Fax: +34 9 45 007014
E-mail: unisleep@jet.es
Dr Yüksel Peker
Sahlgrenska University Hospital, Göteborg (Sweden)
Phone: +46 31 342 1000
Fax: +46 31 824 904
E-mail: yuksel.peker@swipnet.se
Dr Robert Davies
Churchill Hospital Site, Oxford (UK)
Phone: +44 1 865 225236
Fax:+44 1 865 225221
E-mail:
robert.davies@clinical-medicine.oxford.ac.uk
Dr Douglas Bradley
Toronto Hospital (Canada)
Phone: +1 416 340 4719
Fax: +1 416 340 3359
E-mail:
douglas.bradley@utoronto.ca