In addition to its impact on the cardiovascular system and respiration, the condition has the disadvantage of profoundly altering the daily life of sufferers, who are liable to snore and experience sleepiness at work and irritability.

The new "quality-of-life scale" for sleep apnea, prepared by a research team from Quebec and published in this month's European Respiratory Journal (ERJ), shows that this condition has much greater repercussions on patients' emotional lives than previously thought. It appears to be the cause of a hitherto unknown number of nervous breakdowns and problems in social relations.

Sleep apnea is now recognized as a very widespread problem. During sleep, up to a quarter of the population seems to stop breathing briefly at least five times an hour, or every twelve minutes, on average.

When these interruptions occur ten or more times an hour, it becomes a real affliction, known to specialists as obstructive sleep apnea (OSA). While this more serious form only affects some 4% of the population, it is accompanied by numerous other problems.

It is thought, for example, that OSA can considerably increase the risk of death from myocardial infarction or stroke. Moreover, the episodes of daytime sleepiness accompanying the condition can lead to road or workplace accidents.

While it has long been known that OSA causes additional fatigue and irritability because sleep is fragmented, its repercussions on private and social life have, until now, been underestimated, because medical studies were generally limited to strictly physiological criteria.

This is the gap that the researchers of the Center for Pneumology at Laval University, Quebec, under the direction of Dr. Yves Lacasse, have sought to bridge.

As they explain in ERJ, their objective was to describe the impact of OSA on the quality of life of patients suffering from the disease and, subsequently, to construct a quality-of-life scale specifically adapted to OSA.

No mean feat, the task took two years, but it has produced a practically oriented result that promises to have important consequences on the measurement of patients' quality of life.

"The method used in the preparation of this new measuring instrument was similar to that used to produce quality-of-life scales for conditions such as asthma or chronic bronchitis," explains Lacasse.

Initially, the Quebec team drew up an extensive list of 186 different impairments affecting patients suffering from sleep apnea. It was produced on the basis of data from medical literature, specialist opinions and interviews with fifteen patients. The problems ranged from too frequent waking to difficulty in concentrating or staying awake during reading, inconvenience to partners or a feeling of permanent anxiety.

In order to cut the list down to a more manageable size, Lacasse's team tested it on 100 adult patients who had just been diagnosed with OSA. The patients, with an average age of 51, were asked to classify impairments according to the level of nuisance experienced by awarding points between 1 ("this bothers me a little") and 5 ("this bothers me very, very much").

By linking each impairment with the degree of nuisance and the number of patients affected, the Quebec team was able to calculate its "impact score," obtained by multiplying scale of nuisance by frequency.

By retaining only those impairments with an impact score of 1.5 or more, Lacasse and his colleagues were able to further reduce the number to 83. After dividing them into five categories (daytime symptoms, nighttime symptoms, restrictions on activities, emotions and relations with others) and eliminating parameters considered redundant because of overlap, the team finally retained 33 impairments for inclusion in the quality-of-life scale.

As the authors explain in ERJ, examination of the impact score for each of the apnea-linked impairments brings many surprises.

"First of all," says Lacasse, "we were very surprised to see that certain clinical manifestations classically associated with obstructive sleep apnea in the medical literature, such as morning headaches, were reported by a much lower number (48%) than we expected. Other problems, such as stomach acid rising into the esophagus (nocturnal esophageal reflux) were not experienced by any of our patients."

Moreover, while the article in this month's ERJ notes that (predictably) nine out of ten patients complain of unrefreshing sleep, the researchers were surprised by the level of excessive fatigue experienced during the day and the emotional effects.

Not only did that particular impairment affect 77% of patients, but 69% reported feeling "impatient," 59% reported feeling anxious and 53% admitted to feeling depressed.

More than half of patients were reluctant to stay overnight with friends for fear of snoring and three out of four patients reported disturbing their partner's sleep, which can hardly be conducive to marital harmony.

Another detail that surprised the researchers was that 74% of patients admitted to worrying about their weight, which is not reflected anywhere in the existing literature.

The authors were also struck by the fact that the impairments reported by patients differed very little (average impact score 1.40 against 1.55) in relation to whether the sleep apnea had been diagnosed following electrophysiological recording of sleep (polysomnography) or by oxymetry, i.e., continuous measurement of blood oxygen levels, which indicate respiratory interruption.

It is generally considered that oxymetry detects more serious sleep apneas than polysomnography.

"These results suggest, therefore, that physiological data have limited value for assessing the real impact of sleep apnea on patients' daily lives," emphasizes Lacasse, "and that their quality of life is not strongly correlated to the condition's severity, as has also been demonstrated for other respiratory ailments such as chronic bronchitis."

"Quality of life should therefore be measured directly with tailor-made instruments and not estimated indirectly in the sleep laboratory," adds Lacasse.

Since completing the study, the team has been working on developing a simplified self-questionnaire containing a score of questions drawn from the first scale. It is expected to be sensitive enough to measure quality of life changes in the context of clinical tests.

The simplified questionnaire will be compared to other existing questionnaires, not all of them specific to sleep apnea. If found reliable, it will eventually be able to contribute to the development of the sorely needed "gold standard" for the measurement of quality of life in sleep apnea sufferers.

[Contact: Prof. Yves Lacasse]

01-Mar-2002