Epidemiology

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In the general middle-aged population the prevalence of OSAHS ranges between 4-6% in men and 2-4% in women, increasing significantly with advancing age. The difficulty in accessing the costly gold standard polysomnography equipment necessary to make the definitive diagnosis of OSAHS is one of the main reasons why only 5-9% of sufferers have been diagnosed. Alternative diagnostic methods are being investigated in order to avoid such high costs.

Obstructive Sleep Apnea Hypopnea Syndrome (OSAHS), along with insomnia, is one of the most common sleep disorders. Although both conditions are comparable epidemiologically, OSAHS is relatively unknown in the general population. How to diagnose all OSAHS cases is a major medical problem yet to be resolved. A recent study showed that only 6% of medical histories included explicit questions referring to sleep disorders. This underdiagnosis can have fatal consequences. The pathology is often ignored by patients, who, without proper diagnosis, do not know how to cope with the signs and symptoms they face on a daily basis.

In 1993, Young et al took a random sample of 602 workers (male and female) aged between 30 and 60 in order to find out the prevalence of OSAHS. The results were published in the "New England Journal of Medicine" . This was an significant study because up until then the previous epidemiological studies on OSAHS prevalence were restricted to male subjects and the sample was much smaller. Polysomnography was used to calculate the Apnea/Hypopnea Index (AHI) according to gender and age variables. The study concludes, that the estimated prevalence of OSAHS, defined as AHI greater than or equal to 5, was 9% in women and 24% in men. Extrapolating the data to the general population, they estimated that 2% of middle-aged women and 4% of middle-aged men, met the minimum diagnostic criteria for OSAHS. The results also reflected that being male and obese were strongly associated with the presence of OSAHS. Habitual snorers (without gender distinction) tended to have a higher prevalence of OSAHS with an AHI of 15 or more per hour leading to a respiratory disturbance level that merited clinical intervention.

It is estimated that 2-4% of Spain's population meet the diagnostic criteria of OSAHS. In the over 65's, the percentage rises to 25%. In 2001, one of the most complete Spanish population studies was done by Duran et al and published in the "American Journal of Respiratory and Critical Care Medicine". This study showed that OSAHS had a similar incidence when compared to other international studies. Duran et al used a representative sample of the general population between the ages of 30 and 70, taking into consideration a wide spectrum of clinical features, including hypertension, in order to calculate the prevalence of OSAHS. The study was conducted in Vitoria between July 1993 and November 1997 using a random sample of 2,148 subjects and was structured in two parts. The first part of the study had all subjects complete a questionnaire which included questions regarding sleep breathing disorders, snoring, sleepiness, general medical history, medications, alcohol consumption, smoking, demographic and anthropometric data. The clinical examination measured the neck circumference, maximum expiratory flow rate and blood pressure. Subsequently four channel portable polysomnography equipment was used to monitor heart rate, snoring, oxygen saturation and body position during sleep. The second part of the study evaluated those a subgroup with a provisional diagnosis of OSAHS using gold standard conventional polysomnography in a sleep laboratory overnight. The results showed that 35% were habitual snorers and 6% suffered respiratory pauses. Both characteristics occurred more frequently in men, the tendency increasing with age and was associated with OSAHS. Daytime sleepiness was present in 18% of the subjects. An AHI> 10 was found in 19% of men and in 15% of women. The prevalence of OSAHS (AHI> 5) increased with age in both sexes. The AHI was associated with hypertension after adjusting for age, sex, body mass index, neck circumference, alcohol consumption and smoking. This study showed a link between OSAHS and hypertension.

The prevalence of OSAHS in Spain varies depending on different studies. One such study by Marin et al was done in 1997 using a sample of 1360 adults in Zaragoza. It found that OSAHS, defined as snoring, excessive daytime sleepiness and more than 10 episodes of at least 4% desaturation shown by nocturnal pulse oximetry, was present in 2.2% of men and 0.8% of women. In 1995, Zamarrón found studied 693 individuals between 20 and 70 years of age and observed that 6.8% had and AHI >= 5 accompanied by snoring and excessive daytime sleepiness. In a different study done by Solans et al on adults between the ages of 30 and 70 years in Mataró, found that 10% of men and 3.4% of women in their sample had an AHI >= 10 and an Epworth sleepiness scale > 10. All studies concluded that a high prevalence of OSAHS exists and is inextricable linked to hypertension, has a higher incidence in males which progressively increases with age. All studies conclude in a high prevalence of OSAHS a proven relationship with hypertension, higher incidence in males and a progressive increase with age.

As previously stated OSAHS is currently underdiagnosed. Studies detect that only 5-10% of sufferers are diagnoses and treated and in Spain there are approximately 2 million people with severe OSAHS requiring emergency treatment, the majority of whom are still undiagnosed. A very interesting study on undiagnosed cases of OSAHS was performed on patients attending an Ear Nose and Throat (ENT) clinic regarding sleep disorders. After anamnesis and clinical exploration of the upper respiratory tract, all suspected sufferers of OSAHS (14.7%) underwent nocturnal polysomnography. The results showed that 4,78% of these subject had an AHI>5. The authors concluded that "untreated patients are at a higher risk of cardiovascular and neurological complications, have a higher accident rate, reduced quality of life and an increased health care consumption. It is therefore necessary to reduce these consequences by early diagnosis and treatment."

For years, sleep apnea was considered nothing more than a medical curiosity without any real clinical significance and so received little interest. It was associated exclusively with annoying snoring and did not take into account the sociological consequences nor the associated co-morbidity. Until the 90s, research into OSAHS lacked scientific rigour, and it was difficult to find serious studies regarding the prevalence in the general population. The US authorities were the first to understand the severity of OSAHS and were pioneering in establishing guidelines for diagnosis and treatment.
In 1988, the US Congress created the National Research Commission on Sleep Disorders to carry out an exhaustive study on sleep disorders. The aim was to "develop a long-term plan for the use and organisation of national resources and to properly investigate sleep disorders." The Commission reported that the lives of millions of Americas was disturbed, destroyed or interrupted by the consequences of sleep disorders and encouraged researchers and experts in the field to undertake the first epidemiological studies.