The prevalence and related clinical features of obstructive sleep apnea–hypopnea (OSAH) in the general population were estimated in a two-phase cross-sectional study. The first phase, completed by 2,148 subjects (76.9%), included a home survey, blood pressure, and a portable respiratory recording, whereas in the second, subjects with suspected OSAH (n = 442) and a subgroup of those with normal results (n = 305) were invited to undergo polysomnography (555 accepted). Habitual snoring was found in 35% of the population and breathing pauses in 6%. Both features occurred more frequently in men, showed a trend to increase with age, and were significantly associated with OSAH. Daytime hypersomnolence occurred in 18% of the subjects and was not associated with OSAH. An apnea–hypopnea index (AHI) ⩾ 10 was found in 19% of men and 15% of women. The prevalence of OSAH (AHI ⩾ 5) increased with age in both sexes, with an odds ratio (OR) of 2.2 for each 10-yr increase. AHI was associated with hypertension after adjusting for age, sex, body mass index, neck circumference, alcohol use, and smoking habit. This study adds evidence for a link between OSAH and hypertension.
Underdiagnosed obstructive sleep apnea–hypopnea (OSAH) (1, 2) represents a major public health burden (3-9) and further data on the natural and pathophysiological importance of untreated OSAH or accompanying symptoms, particularly daytime hypersomnolence and functional impairment (OSAH syndrome) (10-12), are essential to rational clinical decisions about whom to treat. Epidemiological investigation of OSAH has been hampered by difficulties in obtaining valid data from adequate population-based samples whose diagnosis is based on a full sleep study (polysomnography). Moreover, differences in defining cutoff points for the apnea–hypopnea index (AHI) has contributed to variability in case finding and prevalence estimates of OSAH and OSAH syndrome (13, 14).
We estimated the prevalence of OSAH among a representative sample of the general population of men and women 30 to 70 yr old from Vitoria-Gasteiz, Basque Country (Spain), and investigated the spectrum of clinical features including hypertension associated with sleep-disordered breathing.
Noninstitutionalized people aged 30–70 yr who were residents of Vitoria-Gasteiz (206,116 white population, 20% of people over 65 yr of age, life expectancy at birth 75 yr for men and 83 yr for women), Basque Country, Spain, were eligible to participate in a two-phase prevalence survey. A random stratified one-stage cluster sampling by census areas (n = 7) was drawn from the sampling frame of households using 1991 and 1995 census data for men and women, respectively. Subjects were recruited by mail and by telephone. All eligible participants in a household were invited to take part in the study. The criteria for exclusion were as follows: tracheostomy, serious physical or mental disability, pregnancy, and breastfeeding. The study was done between July 1993 and November 1997. The study was approved by the institutional review board of the Txagorritxu Hospital. Written informed consent was obtained from all participants in the first phase of the study as well as from those selected for overnight polysomnography (second phase).
The first phase of the study included a home-structured interview and sleep recording for one night with the MESAM IV portable recording system. Questionnaires were administered by trained interviewers and included questions on sleep-related breathing disturbances from the Basic Nordic Sleep Questionnaire (15), and questions about respiratory symptoms, medical history, medication use, alcohol consumption, smoking history, and demographic and anthropometric information (height and weight were self-reported). Copies of the interview questionnaire can be obtained from the authors. Habitual snoring was defined as snoring more than 5 d/wk. Information on snoring was primarily obtained from bedpartners (78% of cases), respondents living alone (17% of cases), or other persons living at home (5% of cases). Daytime hypersomnolence (synonymous with excessive daytime sleepiness) was defined as sleepiness at least 3 or more d/wk during the past 3 mo in one or more of the following: after awakening, during free time (leisure time), at work or driving, or during daytime in general. A limited physical examination was performed in which the neck circumference, the peak expiratory flow, and the blood pressure were measured. The neck circumference was measured with a tape measure. The peak expiratory flow was measured with a peak-flow meter (Mini-Wright; HS International, Clement Clarke International, Ltd, E Dinbur, UK). Blood pressure was measured before and after administration of the questionnaire with a mercury sphygmomanometer with the subject seated following the recommendations of the American Heart Association (16). The mean value of these two measures was used for analysis. All interviewers had successfully completed a control phase of 20 video-simulated situations with different degrees of difficulty without significant deviation in the results obtained. Hypertension was defined as systolic blood pressure ⩾ 140 mm Hg or diastolic blood pressure (phase V) ⩾ 90 mm Hg in subjects not taking antihypertensive drugs or self-reporting on current antihypertensive medication. Among the subjects diagnosed as hypertensive, the proportion of cases with systolic blood pressure ⩾ 140 mm Hg or diastolic blood pressure ⩾ 90 mm Hg in people not taking antihypertensive drugs was 75% (81% in men and 66% in women). The MESAM IV (Medizintechnik für Artz und Patient, Munich, Germany) is a four-channel digital recording system that has been previously validated (17, 18). The system records heart rate, snoring, oxygen saturation, and body position and allows both automatic and manual scoring of the recordings.
In the second phase of the survey, all subjects tentatively diagnosed as having OSAH with the portable recording system and a random sample of subjects with negative findings were invited to attend the sleep laboratory for overnight polysomnography. The polysomnography consisted of continuous polygraphic recordings (Alice 3; Respironics Inc., Pittsburgh, OH) from surface leads for electroencephalography (C3/A2 and C4/A1 placements), electrooculography, tibialis electromyography, and electrocardiography, and from noninvasive sensors for nasal and oral airflow (thermistry), tracheal sounds (microphone), thoracic and abdominal respiratory effort (belt sensors, Healthdyne piezoelectric gauge), and oxyhemoglobin level (finger-pulse oximeter [model 340; Palco Laboratories]). The polysomnography records were manually scored using conventional criteria (19). Each 30-s epoch of the recording was scored for sleep stage, breathing, oxygenation, and movement. An abnormal breathing event was defined according to the commonly used clinical criterion of a complete cessation of airflow for ⩾ 10 s (apnea) or a discernible 50% reduction in respiratory airflow accompanied by a decrease of ⩾ 4% in oxyhemoglobin saturation and/or an electroencephalographic arousal (hypopnea). An arousal was defined according to the American Sleep Disorders Association (20). The total number of scored apneas and hypopneas divided by the number of hours of sleep (AHI) was determined for each participant as the summary measure of sleep-disordered breathing. For descriptive analyses, AHI cutoff points of ⩾ 5, ⩾ 10, ⩾ 15, ⩾ 20, and ⩾ 30 were used. The percentage of subjects who had oxygen saturation (SaO2 ) < 90% at least 30% of the time was also calculated. The maximal allowable interval between nocturnal MESAM and polysomnography was 2 mo.
Data analysis was done with common statistical software packages, such as Statistical Analysis Systems (Version 6.12; SAS, Cary, NC) and SUDAAN (Version 7.11). To account for the two-phase design, the analysis was weighted to give unbiased estimates, and the SUDAAN software was used to compute appropriate variances for the weighted analyses. Continuous variables were compared with the t test. Differences in proportions between groups were compared by means of the chi-square (χ2) test. The prevalence odds ratio (OR) and 95% confidence interval (CI) calculated using the multiple logistic regression model (21) were used to estimate the association of age and the prevalence of OSAH adjusted by sex and body mass index (BMI). Logistic regression models were fitted to determine the association between AHI (categorized as 0.0, 0.1–4.9, 5.0–14.9, and ⩾ 15) and daytime hypersomnolence, breathing pauses during sleep, habitual snoring, percentage of subjects who had saturation < 90% at least 30% of the time, and hypertension. The crude OR and 95% CI for each variable by AHI category and the OR adjusted for confounders (age, sex, peak expiratory flow, BMI, neck circumference, alcohol use, and smoking habit) were calculated.
A flow-chart of the study population is shown in Figure 1. Of a total of 2,794 eligible subjects, 81% agreed to take part in the study and 95% of these completed the first phase of the survey. Results of MESAM were suggestive of OSAH in 442 (21%) patients. A final sample of 390 patients with a tentative diagnosis of OSAH (255 men, 135 women) and 165 (69 men, 96 women) from a subsample of 305 diagnosed as not having OSAH underwent polysomnography. Subjects who agreed to undergo polysomnography and those who refused in both subsamples of patients with and without OSAH according to results of MESAM showed similar frequencies with regard to their responses to all questionnaire items on sleep characteristics, body habitus, sex, and age.
Results of the 2,148 subjects who completed the first phase of the study stratified by sex are shown in Table 1. Both men and women tentatively diagnosed as having OSAH by MESAM were significantly older, had a higher BMI, and a higher prevalence of hypertension than subjects diagnosed as not having OSAH. Habitual snoring was found in 35% of the population, breathing pauses in 6%, and daytime hypersomnolence in 18%. According to sex, habitual snoring occurred in 46% of men and 25% of women and showed a significant trend to increase with age (from 35% and 11% in the 30–39 year age group to 49% and 41% in the 60–70 yr age group for men and women, respectively). Breathing pauses during sleep on at least 3 d/wk were reported by 10% of men and 2.5% of women and also increased with age. Daytime hypersomnolence found in 14% of men and 22% of women was not associated with age.
|OSAH (n = 283)||No OSAH (n = 767)||OSAH (n = 159)||No OSAH (n = 939)|
|Age, yr||52.0 (9.9) *,†||47.4 (10.8)||55.5 (11.3)†||46.9 (10.5)|
|Body mass index, kg/m2||27.5 (3.4)†||25.7 (2.9)||28.4 (6.0)†||24.5 (3.9)|
|Body mass index > 30 kg/m2, %||22†||8||32†||18|
|Systolic blood pressure, mm Hg||131.4 (17.1)‡||129.0 (16.4)||129.8 (19.1)†||120.8 (16.6)|
|Diastolic blood pressure, mm Hg||82.5 (10.1)‡||81.2 (9.2)||80.0 (11.2)†||76.4 (18.2)|
|Sleep during the week, h||7.0 (1.4)||7.1 (1.3)||7.0 (1.6)||7.1 (1.3)|
|Sleep at weekend, h||7.8 (1.7)||7.9 (1.4)||7.5 (1.7)||7.8 (1.5)|
|MESAM IV, manual scoring results||23.5 (13.7)||4.7 (3.2)||22.5 (11.0)||4.3 (3.1)|
|Agreed to participate§||23.8 (14.1)||5.4 (3.3)||21.9 (9.3)||6.2 (4.2)|
|Did not agree to participate§||21.3 (10.4)||4.7 (2.4)||22.5 (11.3)||5.4 (3.9)|
A wide range of sleep-disordered breathing, ranging from AHI scores of 0 to 120 in men and of 0 to 59 in women, was found. Criteria of AHI values ⩾ 10 on polysomnography were not met by 45.1% of men and 65.4% of women diagnosed as having OSAH by MESAM, whereas 5.8% of men and 11.2% of women not suspected of having OSAH met criteria on polysomnography. The cumulative proportion of subjects with OSAH was similar in both sexes for AHI values < 8, but thereafter men had a greater prevalence of OSAH than women. Prevalence estimates for different cutoff points of AHI are shown in Table 2. Men had a higher prevalence of OSAH than women in all age groups and at all cutoff points for the AHI ⩾ 5 except for the stratum 50–59 yr at the ⩾ 5 cutoff point. The prevalence of OSAH increased with age in both sexes, with an OR of 2.2 (95% CI, 1.7 to 3.0) for a 10-yr increase and for an AHI ⩾ 5. The male/female OR adjusted by age and BMI increased from 1.2 (95% CI, 0.7 to 2.0) for a cutoff point of ⩾ 5 to 3.0 (95% CI, 1.1 to 8.2) for a cutoff point of ⩾ 30.
|Data||Percentage of Subjects (95% Confidence Interval)|
|⩾ 5||⩾ 10||⩾ 15||⩾ 20||⩾ 30|
|All ages, yr||26.2 (20–32)||19.0 (14–24)||14.2 (10–18)||9.6 (7–12)||6.8 (5–9)|
|30–39||9.0 (2–16)||7.6 (0–15)||2.7 (1–5)||2.1 (0–4)||2.1 (0–4)|
|40–49||25.6 (14–37)||18.2 (9–27)||15.5 (7–24)||10.1 (5–15)||7.0 (3–11)|
|50–59||27.9 (17–38)||24.1 (15–34)||19.4 (11–27)||14.7 (8–21)||11.4 (6–17)|
|60–70||52.1 (33–71)||32.2 (17–48)||24.2 (12–37)||15.0 (8–22)||8.6 (4–14)|
|All ages, yr||28.0 (20–35)||14.9 (9–20)||7.0 (3–11)||6.0 (2–9)||2.9 (0–5)|
|30–39||3.4 (0–7)||1.7 (0–4)||0.9 (0–2)|
|40–49||14.5 (3–25)||9.7 (0–19)|
|50–59||35.0 (20–50)||16.2 (5–27)||8.6 (1–17)||8.3 (0–16)||4.3 (0–10)|
|60–70||46.9 (31–63)||25.6 (13–38)||15.9 (6–26)||13.0 (3–22)||5.9 (0–13)|
The association between different scores of AHI and clinical features of OSAH adjusted by age, sex, and peak expiratory flow is shown in Table 3. Breathing pauses during sleep, habitual snoring, and the percentage of subjects who had saturation < 90% for at least 30% of the time were significantly associated with OSAH. By contrast, daytime hypersomnolence was not associated with OSAH. As shown in Table 4, AHI was associated with hypertension after adjustment for age, sex, BMI, neck circumference, alcohol use, and smoking habit.
|OR and 95% CI for Clinical Features of OSAH||AHI Category|
|Crude||1.0||0.81 (0.4 to 1.7)||1.37 (0.6 to 3.1)||1.05 (0.3 to 2.2)|
|Adjusted for age and sex||1.0||0.98 (0.4 to 2.2)||1.37 (0.6 to 3.3)||1.05 (0.3 to 3.3)|
|Breathing pauses during sleep|
|Crude||1.0||0.54 (0.1 to 3.0)||4.63 (0.8 to 28.4)||13.40 (2.6 to 70.5)|
|Adjusted for age and sex||1.0||0.42 (0.1 to 2.4)*||4.51 (0.8 to 26.4)*||9.74 (1.8 to 51.7)*|
|Crude||1.0||2.88 (1.4 to 5.9)||3.36 (1.5 to 7.7)||5.45 (2.4 to 12.2)|
|Adjusted for age and sex||1.0||2.63 (1.2 to 5.6)†||3.20 (1.4 to 7.5)†||4.72 (1.9 to 11.5)†|
|Percentage of subjects with|
|SaO2 < 90% at least 30% of|
|the total sleep time|
|Crude||1.0||3.71 (1.4 to 9.6)||3.46 (1.5 to 8.3)||15.57 (7.31 to 34.3)|
|Adjusted for age, sex, and|
|peak expiratory flow||1.0||2.69 (1.0 to 7.3)†||3.35 (1.3 to 8.7)†||9.74 (4.1 to 23.0)†|
|0 (n = 117)||0.1–4.9 (n = 169)||5.0–14.9 (n = 115)||⩾ 15 (n = 151)|
|Odds ratio (95% CI)|
|Crude||1.0||3.74 (1.69 to 8.31)||3.07 (1.26 to 7.51)||6.46 (2.79 to 14.95)|
|Adjusted for age|
|and sex||1.0||2.76 (1.19 to 6.41)||1.70 (0.68 to 4.29)||2.91 (1.19 to 7.07)|
|Adjusted for BMI and|
|neck circumference||1.0||2.58 (1.09 to 6.09)||1.37 (0.56 to 3.36)||2.25 (0.90 to 5.63)|
|Adjusted for BMI,|
|alcohol use, and|
|smoking habit||1.0||2.47 (1.06 to 5.76)||1.30 (0.54 to 4.14)||2.28 (0.92 to 5.66)|
This study confirms that OSAH is very prevalent in the general population and that the frequency of this disorder increases with age. The present results are strengthened by the very high response rate of 81%. Our findings of habitual snoring in 35% of the population, breathing pauses in 6%, and daytime hypersomnolence in 18% are consistent with those found by others (13, 22, 23) and indicate that symptoms of OSAH are common in the general population. In contrast, evidence on the prevalence of OSAH in the general population using conventional polysomnography is lacking. In a random sample of 1,255 employed people 30–60 yr old, Young and coworkers (13) found that 9% of women and 24% of men met minimal criteria for OSAH, and when results were extrapolated to the general population, it was estimated that 2% of women and 4% of men had OSAH syndrome. In a general random sample of 741 men aged 20–100 yr, Bixler and coworkers (14) reported AHI ⩾ 10 and daytime symptoms in 3.3% of the sample.
Data on participation by census area for both men and women reveal that participation was lower for men in census area 1 and for women in census areas 1 and 2, but the estimated prevalence of OSAH for the different AHI cutoff points did not vary significantly when these areas were excluded from the calculations (data not shown). We found that the overall prevalence of OSAH of 26.7% was higher in our general population (26.2% in men and 28% in women with AHI ⩾ 5) than that reported by Young and coworkers (13) in the Wisconsin Sleep Cohort Study. This may be explained by differences in the health status of the population (healthy worker effect in Young's study), in the age span (30 to 60 yr in the study of Young and coworkers (13) versus 30 to 70 yr in our study), in the definition of hypopnea (arousal criterion was not applied in the study of Young and coworkers), or in the ethnic characteristics of the populations (only white people in our sample) (24). Discrepancies encountered were more relevant for women than for men. In the Wisconsin study (13), men were 2.0 to 3.7 times as likely as women to have sleep-disordered breathing, whereas when data in our study were adjusted by age and BMI, the male/female OR were 1.2 and 3.0 for an AHI ⩾ 5 and ⩾ 30, respectively.
Most studies had shown how the prevalence of OSAH increases with age (13, 14, 25, 26). Redline and coworkers (25) carried out a study on 390 community residents of the Cleveland Family Study, from children to older aged people, and found that prevalence rates for an AHI ⩾ 5 increased close to fivefold for the group younger than 25 yr of age to subjects over 60 yr of age and that this increase was also consistent for higher AHI cutoff values. In the Wisconsin study (13), there was a pattern of increasing prevalence with age for AHI ⩾ 5 being less evident for AHI ⩾ 10 or ⩾ 15. We found a strong association between AHI and age in the logistic regression model adjusted by sex and BMI, suggesting that factors other than obesity play a role in the presence of OSAH.
The definition of OSAH is arbitrary and it has been suggested than an AHI ⩾ 5 is a too low cutoff value, especially for elderly people (27, 28). Recently, the American Academy of Sleep Medicine (AASM) (29) proposed a consensus definition for OSAH syndrome based on an AHI ⩾ 5 plus symptoms.
The prevalence of OSAH syndrome of 4% in men and 2% in women estimated by Young and coworkers (13) was based on AHI score of 5 or higher and moderate to severe daytime hypersomnolence. In a sample of a male population using a definition of OSAH syndrome of AHI ⩾ 10 plus daytime sleepiness, hypertension, or another cardiovascular complications, Bixler and coworkers (14) found a prevalence of 3.3%. According to an AHI ⩾ 10 plus excessive daytime sleepiness, the prevalence of OSAH syndrome in our population was 3.4% in men and 3% in women.
In our study, daytime hypersomnolence was found in 21% of men and 26% of women with AHI ⩾ 5, but excessive sleepiness was also found in 12% of the men and 28% of the women with AHI < 5. Thus, excessive daytime hypersomnolence is highly prevalent both in patients with and without OSAH. Moreover, a significant association between daytime hypersomnolence and OSAH was not found. On the other hand, self-reported sleepiness is not an objective measure and it underestimates the physiological state of sleepiness (30). Thus, it seems difficult to accurately define OSAH syndrome in the general population according to a low AHI score and excessive daytime sleepiness.
In contrast to a systematic review in which no firm evidence for the contribution of OSAH to hypertension was demonstrated (31), it has been recently shown that sleep-disordered breathing and hypertension are clearly linked (32-35). In agreement with these findings, a significant association of AHI with hypertension was found after adjusting for demographics (age, sex) and anthropometric variables (including BMI and neck circumference), as well as for alcohol intake and smoking. In our study, however, the odds ratio of hypertension did not increase by AHI category, which is in contrast to data found in patients referred to the sleep clinic with suspected sleep apnea syndrome (33). In this study, Lavie and coworkers (33) showed that each additional apneic event per hour of sleep increased the odds of hypertension by 1%. Young and coworkers (32), also showed that the prevalence of hypertension trended to increase with increasing severity of sleep-disordered breathing. A dose–reponse association between sleep-disordered breathing at baseline and the presence of hypertension 4 yr later that was independent of known confounding factors was found in the prospective, population-based study of Peppard and coworkers (34). The relatively small sample size in our study compared with the large number of participants in studies reported by other authors (32-35) may account for our observation of a nonincreasing trend in the odds ratios for the presence of hypertension comparing the highest and the lowest category of AHI.
In summary, we found that the prevalence of OSAH in the general population was high and increased with age in both sexes. Habitual snoring and breathing pauses were significantly associated with OSAH. This study adds evidence for a link between OSAH and hypertension.
Joaquı́n Durán and Santiago Esnaola were the principal investigators, designed the protocol, collected data, and wrote the paper. Ramón Rubio and Joaquı́n Durán analyzed polysomnographic and polygraphic recordings. Santiago Esnaola performed the statistical analysis. Ángeles Iztueta designed the sampling plan. The final draft was revised and approved by all authors. The authors are grateful to Dr. E. Gorostiza for training the interviewers in the blood pressure measurement, to J. M. Montserrat, E. Ballester, and D. Rodenstein for reading the draft and for helpful comments on the manuscript, to M. Partinen for the use of the Basic Nordic Sleep Questionnaire, to T. Calleja, G. De La Torre, B. Larrauri, and I. Toña for technical contributions to the study, and to Marta Pulido for editing the manuscript and editorial assistance. The MESAM IV devices used for nocturnal respiratory polygraphic recordings were kindly lent by Medizintechnik für Arz und Patient from Munich, Germany.
This study was supported by grants from Fondo de Investigación Sanitaria (FIS 93/0553 and 95/1176) of the Ministry of Health, Department of Health, Basque Government (1992 and 1995), Spanish Society of Pneumology and Thoracic Surgery (SEPAR) (1996), and Caja Vital-Kutxa (1994).
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