RESPIRATORY MEDICINE (2000) 94, 356±363 doi:10.1053/rmed.1999.0715, available online at http://www.idealibrary.com on in relation to symptoms in chronic respiratory diseaseða nationally representative population study L. VON HERTZEN*, A.REUNANEN {,O.IMPIVAARA {,E.MAÈ LKIAÈ } AND A. AROMAA { *The Finnish Lung Health Association, Sibeliuksenkatu 11 A 1, FIN-00250 Helsinki, { National Public Health Institute, Mannerheimintie 166, FIN-00300 Helsinki, { The Social Insurance Institution, Peltolantie 3, FIN-20720 Turku and } University of JyvaÈskylaÈ, P.O. Box 35, FIN-40351 JyvaÈskylaÈ, Finland We examined the severity of airway obstruction and the occurrence of respiratory symptoms in a large, nationally representative population sample and in a subgroup of subjects with chronic bronchitis and/or emphysema to obtain information for developing national prevention and treatment strategies for these diseases. The study population comprised of 7217 randomly selected subjects (aged 30 years and older) who participated in a comprehensive health examination survey. The `cases' were subjects diagnosed as having chronic bronchitis and/or emphysema. The survey methods comprised of questionnaires, interviews, physical measurements, including spirometry, and clinical examinations. In the whole study population, the age-adjusted prevalence of chronic bronchitis and/or emphysema was 22% among men and 7% among women, whilst clinically relevant airways obstruction (FEV 1 /FVC% 69) was present in 11% of men and in 5% of women.the occurrence of chronic cough and phlegm production was lowest among the `cases' with pronounced obstruction (in 68% of men with severe and in 60% of women with moderate obstruction), whereas cold air-associated dyspnoea aggravation showed an inverse relationship, occurring most commonly in men ( 80%) with severe obstruction. Unexpectedly, half of the bronchitic women had never smoked. We conclude that the occurrence of certain bronchitic symptoms, such as chronic cough and phlegm production and cold air-associated dyspnoea aggravation, may to some degree indicate di erent stages of the disease. Smoking was not closely associated with air ow limitation in women here. Key words: chronic bronchitis; chronic obstructive pulmonary disease; lung function; obstruction; symptoms. RESPIR. MED. (2000) 94, 356±363 # 2000 HARCOURT PUBLISHERS LTD Introduction Chronic obstructive pulmonary disease (COPD), the most common chronic respiratory disease in industrialized countries, is a widely under-rated and under-investigated disease (1). This has been largely explained by the fact that the disease cannot be cured (2). The prognosis has been especially poor in symptomatic patients who continue to smoke (3). Although COPD develops primarily in smoking men, even severe COPD has been observed in men and women who have never smoked (4). Moreover, impaired lung function has been shown to predict mortality and morbidity for a range of diseases, both in smokers and in lifetime non-smokers (5±7). It is well known that in many patients with even moderate obstruction the disease has not been diagnosed Received 14 April 1999 and accepted in revised form 29 September 1999. Correspondence should be addressed to: Dr. Leena von Hertzen, The Finnish Lung Health Association, Sibeliuksenkatu 11 A 1, FIN-00250 Helsinki, Finland. Fax: +358 9 454 21 282; E-mail: lvhertzen@ lha. (8,9). The development of dyspnoea is slow and gradual and often gives no cause for consulting a doctor until severe dyspnoea has developed (8). COPD is characterized by air ow limitation associated with chronic bronchitis or emphysema (6). Spirometry has been established as the primary method of diagnosing COPD and assessing its severity, progression and prognosis. can be de ned as reduced forced expiratory volume in 1 sec (FEV 1 ) in relation to forced vital capacity (FVC) or to reference values (9). Attention has recently been refocused on the value of spirometry as part of health assessments in middle-aged populations (5). Information on the severity pattern of airway obstruction in nationally representative population samples is limited. Little is also known about the occurrence of respiratory symptoms in patients with chronic bronchitis and emphysema with respect to the stage of the disease. Such information is needed, not only for obtaining a better insight into the natural history of the disease, but also for developing guidelines for preventive and therapeutic strategies. The aim of the present study was, rstly, to examine the severity pattern of airway obstruction in a large, nationally representative population sample and, 0954-6111/00/040356+08 $35?00/0 # 2000 HARCOURT PUBLISHERS LTD
RESPIRATORY SYMPTOMS AND SEVERITY OF AIRWAY OBSTRUCTION 357 secondly, to study the occurrence of respiratory symptoms in relation to observed obstruction in a subgroup of subjects with chronic bronchitis and/or emphysema. Subjects and methods The present work was part of a large-scale population study, the Mini-Finland Health Survey, comprising a nationally representative sample of 8000 persons, 3637 men and 4363 women, aged 30 years or over. The sampling was performed using a two-stage strati ed cluster design. Randomly selected persons were investigated in each of the 40 study areas representing equitably all parts of the country, both city and rural areas. The distribution of the study population by age, marital status and education closely resembled those for the whole population of the country. The study consisted of two phases, a screening phase and a re-examination phase. With the invitation to attend the screening phase the subjects received a basic questionnaire including questions on physician-diagnosed chronic diseases. The clinical examinations, comprising also symptom interviews, spirometry and X-rays, were performed by a mobile clinic unit. Those with a disease history, or any symptom or nding suggesting cardiovascular or respiratory disease, were invited to attend the re-examination phase a few months later. This included a comprehensive clinical examination by a physician. Smoking habits were recorded, and those who had been regular smokers (cigarettes, cigars or pipe tobacco) for at least 1 year and continued to smoke were de ned as current smokers. Those who had been regular smokers but had quit smoking, whatever the time-point, were considered former smokers, and those who had never smoked regularly were classi ed as never-smokers. A standardized questionnaire was used to record symptoms suggesting respiratory diseases, including dyspnoea (10,11). Lung function was measured with the Vitalograph 1 (Vitalograph Ltd., Buckingham, U.K.) spirometer, and the results were corrected to BTPS (body temperature and pressure, saturated with water vapour). Results of two technically faultless measurements were recorded, and the highest readings of FEV 1 and FVC were taken as the nal results, whether obtained at the same measurement or not. The only reason to reject a measurement was a technically incomplete or otherwise unsuccessful blow. The calibration of the spirometer was performed according to manufacturer's instructions. comprised of all those subjects who, according to the examining physician, met the criteria of chronic bronchitis or emphysema or both. Chronic bronchitis was de ned according to the established criteria (12,13) as cough with phlegm production on most days for at least 3 months a year during at least 2 consecutive years, excluding other diseases that could explain the symptoms. Emphysema was diagnosed on the basis of physical examination and chest radiographs as permanent abnormal enlargement of the gasexchanging airspaces, accompanied by destruction of alveolar wells but not by obvious brosis (14,15). Two trained radiologists independently read all the chest radiographs. of any degree was de ned as FEV 1 less than 80% of FVC. The severity of obstruction was graded as followsðfev 1 /FVC%: 70±79%, minimal to mild; 50±69%, moderate; 550%, severe. Only moderate to severe obstruction (FEV 1 /FVC% equal to or less than 69) was considered clinically relevant. For minimal to mild obstruction, the term `mild' is used in the tables. A total of 7217 (90.2% of the sample) subjects, 3322 men and 3895 women, participated in the study. Spirometric measurements were obtained from 7008 subjects. The subgroup of `cases' comprised a total of 988 subjects, 719 men and 269 women, diagnosed as having chronic bronchitis and/or emphysema. STATISTICAL METHODS Continuous variables are expressed as means (standard deviation, SD) and prevalences as directly standardized ageadjusted values. Logistic regression analysis was used to calculate odds ratios (OR) with 95% con dence intervals (CI), and these were also used to test the statistical signi cance of the di erence between the `cases' and others. Results Age distribution and clinical characteristics of the whole study population and the `cases' are given in Table 1, and the prevalences of major chronic respiratory diseases by age group and gender in Table 2. Among the men with chronic bronchitis and/or emphysema de ned as `cases', 521 (72%) had chronic bronchitis only, 91 (13%) had emphysema only and 107 (15%) had both diseases. Among women, 239 (89%) had chronic bronchitis only, 24 (9%) emphysema only and six (3%) had both. The age-adjusted prevalence of asthma or any other respiratory disease (sarcoidosis, cystic brosis, bronchiectasis and bronchiolitis obliterans) was 3% in both men and women. The proportion of clinically relevant obstructions was 11% (352 of 3255) among men and 5% (192 of 3753) among women in the whole population. The respective gures for the `cases' only were 27% (196 of 719) in men and 18% (47 of 269) in women. No bronchitic women su ered from severe obstruction and only eight (0.2%) such women were found in the whole population (Table 3). Overall, when even minimal to mild changes were taken into consideration, 47% of men and 39% of women showed air ow limitation to some degree (Table 3). The proportion of current smokers was 36% for men and 13% for women in the population, and respectively 72% and 45% among the `cases' only (Table 1). Table 4 gives the age-adjusted prevalences of current, former and neversmokers by severity of airway obstruction. Unexpectedly, half of the women with chronic bronchitis and/or emphysema had never been regular smokers.
358 L. VON HERTZEN ET AL. TABLE 1. Characteristics of subjects with chronic bronchitis and/or emphysema (`cases') and the whole study population (all) All All Men Men N 719 269 3322 3895 Age distribution, n (%) 30±44 years 206 (29) 83 (31) 1343 (40) 1373 (35) 45±54 177 (25) 55 (20) 781 (24) 828 (21) 55±64 138 (19) 62 (23) 603 (18) 745 (19) 65±74 152 (21) 45 (17) 436 (13) 642 (17) 4 74 46 (6) 24 (9) 159 (5) 307 (8) Spirometric ndings* FEV 1 l mean (SD) 32 (11) 24 (08) 38 (10) 28 (07) FVC l mean (SD) 43 (12) 31 (08) 48 (11) 34 (08) FEV 1 /FVC% mean (SD) 740 (113) 782 (87) 790 (82) 811 (67) Smoking, n (%) Current 519 (72) 120 (45) 1206 (36) 497 (13) Former 136 (19) 12 (5) 1136 (34) 369 (10) Never 63 (9) 137 (51) 974 (29) 3025 (78) Cigarettes per day, n (%) 1±9 50 (7) 28 (10) 171 (5) 200 (5) 10±19 155 (22) 50 (19) 421 (13) 182 (5) 20±29 217 (30) 40 (15) 391 (12) 105 (3) 30 73 (10) 2 (07) 138 (4) 7 (02) Pipe tobacco/cigars regularly**, n (%) 24 (3) Ð 85 (3) 3 (008) Concomitant diseases, n (%) Cardiovascular 266 (37) 91 (34) 927 (28) 1122 (29) Other respiratory 55 (8) 31 (12) 141 (4) 159 (4) Musculoskeletal 338 (47) 150 (56) 1164 (35) 1773 (46) *data not available in 67 men and 142 women; **daily or nearly daily. TABLE 2. Prevalences (%) of major chronic respiratory diseases by age and gender in the whole study population Age-group (years) 30±44 45±54 55±64 65±74 474 All (age-adjusted) (n) Men Chronic bronchitis 154 218 197 266 193 193 (521) Emphysema 02 30 91 218 193 61 (91) Chronic bronchitis and/or emphysema 154 229 236 364 317 221 (719) Asthma 06 22 21 22 07 14 (26) Chronic bronchitis 61 65 84 60 49 65 (239) Emphysema 00 05 04 18 49 08 (24) Chronic bronchitis and/or emphysema 61 67 85 75 99 72 (269) Asthma 16 26 21 28 37 22 (58)
RESPIRATORY SYMPTOMS AND SEVERITY OF AIRWAY OBSTRUCTION 359 TABLE 3. Severity of airway obstruction in men and women according to the presence of chronic respiratory diseases in the whole study population Chronic bronchitis (only) Emphysema (only) Chronic bronchitis and/or emphysema Asthma or other chronic respiratory disease* No respiratory disease All Men, n (%) None 233 (45) 14 (15) 257 (36) 24 (30) 1459 (59) 1740 (54) Mild 212 (41) 31 (34) 266 (37) 36 (45) 861 (35) 1163 (36) Moderate 70 (13) 34 (37) 158 (22) 20 (25) 136 (6) 314 (10) Severe 6 (1) 12 (13) 38 (5) 0 (0) 0 (0) 38 (1) Total 521 (100) 91 (100) 719 (100) 80 (100) 2456 (100) 3255 (100) Any degree of 288 (55) 77 (85) 462 (64) 56 (70) 997 (41) 1515 (47) obstruction, n (%), n (%) None 132 (55) 0 (0) 134 (50) 35 (30) 2106 (63) 2275 (61) Mild 77 (32) 11 (46) 88 (33) 53 (45) 1145 (34) 1286 (34) Moderate 30 (13) 13 (54) 47 (18) 27 (23) 110 (3) 184 (5) Severe 0 (0) 0 (0) 0 (0) 3 (3) 5 (01) 8 (02) Total 239 (100) 24 (100) 269 (100) 118 (100) 3366 (100) 3753 (100) Any degree of obstruction, n (%) 107 (45) 24 (100) 135 (50) 83 (70) 1260 (37) 1478 (39) *sarcoidosis, cystic brosis, bronchiectasis or bronchiolitis obliterans. TABLE 4. Age-adjusted prevalences (%) of current, former and never-smokers according to severity of airway obstruction in men and women with chronic bronchitis and/or emphysema (`cases') Smoking status Current Former Never Men % % % None 663 200 137 Mild 719 210 71 Moderate 745 197 53 Severe 557 344 99 Total 722 189 88 Other 254 393 352 Whole population 361 343 295 OR (95% CI)* 98 (80±121) 03 (03±04) 02 (01±03) None 365 56 579 Mild 476 31 493 Moderate 441 58 500 Total 446 45 509 Other 104 98 797 Whole population 131 97 771 OR (95% CI)* 87 (65±117) 06 (04±11) 02 (02±03) *OD: odds ratio for the di erence between `cases' and others; CI: con dence interval.
360 L. VON HERTZEN ET AL. OCCURRENCE OF RESPIRATORY SYMPTOMS IN RELATION TO SEVERITY OF AIRWAY OBSTRUCTION AMONG THE `CASES' Analysis of the occurrence of respiratory symptoms among the `cases' strati ed by the severity of air ow impairment revealed that the occurrence of chronic cough and phlegm production were lowest in subjects with advanced obstruction (in 68% of men with severe and in 60% of women with moderate obstruction) (Table 5). In contrast, cold airassociated aggravation of dyspnoea was reported by most `cases' with severe (80% of men) or moderate (73% of women) airway obstruction, and in those with no obstruction, this symptom was experienced by only about one third of the subjects (35% of men and 30% of women). This aggravation of dyspnoea was generally more common in women with obstruction than in such men, even if the gender di erence did not achieve statistical signi cance (Table 5). Severe dyspnoea (Grades 3±4) was present in 10% of the bronchitic men, and in 9% of the bronchitic women, and, TABLE 5. Age-adjusted prevalences (%) of chronic cough and phlegm production and cold air-associated dyspnoea aggravation according to severity of airways obstruction in men and women with chronic bronchitis and/or emphysema (`cases') Chronic cough and phlegm production % Cold air associated dyspnoea aggravation % Men None 828 354 Mild 842 326 Moderate 814 527 Severe 682 802 Total 836 383 Other 72 112 Whole population 238 165 OR (95% CI)* 420 (321±550) 47 (38±57) None 961 297 Mild 848 446 Moderate 601 725 Total 870 424 Other 82 170 Whole population 138 186 OR (95% CI)* 393 (268±577) 38 (29±50) *See legend for Table 4. as expected, was associated with severe airway obstruction. However, 55% of the bronchitic men with such severe obstruction had experienced only mild or no dyspnoea at all (Table 6). Discussion AIRWAY OBSTRUCTION Eleven per cent of all the men and 5% of all the women in the present study showed clinically relevant airway obstruction. In agreement with our results, Isoaho et al. reported a prevalence of 125% for men and 3% for women in an elderly Finnish population (16). Other studies with unselected populations from Norway (17) and Denmark (18) have shown lower prevalences (4±5% for both genders). However, due to the inconsistency in the obstruction criteria and age structures of the populations, any comparison between di erent studies must be taken with great caution. It has recently been shown that reduced FEV 1 signi cantly increases mortality from all causes, both among men and women, and that the association persists after controlling for smoking, age and other risk factors (5,19,20). The increased risk of death was apparent even for subjects with relatively mild function impairment (5). Not even mild impairment without major symptoms should therefore be ignored. Indeed, no distinct symptoms appear to occur in most patients with chronic air ow limitation; the disease may proceed unrecognized until severe and irreversible loss of FEV 1 has occurred (8). Therefore, as our aim here was to detect even the most subtle changes associated with early stages of the disease, we included even minimal to mild obstruction as an own category in the analysis. Thus, according to the criteria used here, nearly half of all the men and about 40% of all the women showed some degree of airways obstruction, although we cannot exclude the possibility that some of these subjects may have had undiagnosed asthma, or that in some instances the ndings may have resulted from technically incomplete spirometry. However, as quality aspects are of utmost importance in spirometry (21), special attention was devoted here to quality assurance, calibration of the spirometer and reproducibility of the measurements. The severity criteria were based on the FEV 1 /FVC% values instead of FEV 1 % of predicted, because the reference values for the Finnish population were obtained from a selected population sample with a spirometry other than Vitalograph. The ratio of the actual measured values was considered to be a useful tool for the purpose of this study. RESPIRATORY SYMPTOMS IN RELATION TO SEVERITY OF AIRWAY OBSTRUCTION We found that half of the bronchitic women who had clinically relevant airways obstruction had never been regular smokers, indicating that in many women chronic cough and phlegm production and the development of
RESPIRATORY SYMPTOMS AND SEVERITY OF AIRWAY OBSTRUCTION 361 TABLE 6. Age-adjusted prevalences (%) of dyspnoea according to severity of airway obstruction in men and women with chronic bronchitis and/or emphysema (`cases') Grade of dyspnoea** 0±1% 2% 3% 4% Men None 663 165 56 81 Mild 754 188 24 31 Moderate 613 296 34 57 Severe 293 254 78 358 Total 694 203 35 61 Other 891 77 13 11 Whole population 858 101 17 21 OR (95% CI)* 03 (02±04) 27 (22±35) 22 (13±38) 46 (28±75) None 793 136 41 30 Mild 672 225 62 42 Moderate 534 359 41 67 Total 699 211 48 41 Other 826 125 26 17 Whole population 829 128 25 17 OR (95% CI)* 05 (03±06) 18 (13±25) 24 (14±41) 38 (22±66) *See legend for Table 4; **Dyspnoea Grades: 0±1, none or minimal; 2, mild; 3, moderate; 4, severe according to Rose et al. (11). airway obstruction may not be associated with smoking. Similarly, LundbaÈ ck et al. have found that a considerable proportion of women with chronic bronchitis are nonsmokers (22). Alpha-1-antitrypsin de ciency does not explain our nding, since the prevalence of the ZZ phenotype of this de ciency in Finland has been estimated to be only 002% (23). The possible role of persistent infection (24,25) cannot be ruled out, neither can that of occupational exposure nor passive smoking, and these associations may remain uncovered in men due to the overwhelming impact of smoking. It is also possible that some asthmatics have been categorized into `cases', since provocation tests could not be performed in this large-scale population survey. Asthma diagnosis was mainly based on anamnesis and a speci c symptom questionnaire. This may also partly explain the relatively low prevalence of asthma here. The most important and disabling symptom in COPD patients is dyspnoea (26). In the Whitehall Study, both dyspnoea and low FEV 1 (percentage of the predicted) were independent predictors of mortality from chronic respiratory and cardiovascular diseases and from all causes (20). In the present study, more than half of both men and women with moderate obstruction and more than a quarter of men in whom obstruction was severe had no pathological (Grades 2±4) dyspnoea. Similar results have been reported previously (16). Since dyspnoea is the symptom most likely to lead patients with COPD to seek medical help (26), the disease is often diagnosed late in its course. Indeed, a recent health survey of an elderly population revealed that only about half of the cases with COPD had been previously diagnosed (16). Chronic cough and phlegm production was presentð consistently with our diagnostic criteriaðin most of the `cases', although these symptoms were less common in subjects with clinically relevant obstruction than in those with mild or no obstruction at all. Our results are in agreement with those of Linde n et al., who reported that in ammatory cells are found in bronchoalveolar lavage (BAL) to a lesser extent in patients with obstructive chronic bronchitis than in patients with non-obstructive chronic bronchitis (27). In the more advanced stages of the disease, the deposition of connective tissue in the epithelium may not allow the migration of in ammatory cells to the airspace. This could then result in less phlegm production and cough in patients with moderate to severe obstruction. In the landmark study of COPD in working men, Fletcher et al. (28) found that COPD consists of a hypersecretory disorder and a distinct obstructive disorder commonly associated with each other. The main factors determining
362 L. VON HERTZEN ET AL. susceptibility to these disorders are not known, but they are presumed to be at least partly genetically determined (28). Mucus hypersecretion alone has not been associated with increased mortality (29), although recent research has provided evidence that mucus hypersecretion may be related to lung function impairment even after adjustment for baseline FEV 1 and smoking status (30). Pathophysiologically, symptoms of chronic bronchitis are not considered to be of any major adverse signi cance and therefore chronic bronchitis may rather serve as a harbinger of risk for the development of obstruction in later life (31). The subjects with non-obstructive chronic bronchitis did not actually di er from the population as a whole in any other aspect than the occurrence of chronic cough and phlegm production. Weather (cold air)-associated aggravation of dyspnoea was related to the severity of the disease. In agreement with the present study, airway hyper-responsiveness was commonly found in patients with COPD, related to the degree of obstruction (32). Moreover, this symptom has been associated with the female gender (33) and smoking (33,34). In the present study, smoking appeared not to be closely associated with this symptom, since it was especially common in women with clinically relevant obstruction, half of whom had never been regular smokers. Obstruction and hyper-responsiveness may develop independently of each other, sharing a common cause, for example persistent in ammation (32). Bronchial hyper-responsiveness present in COPD seems to di er from that occurring in asthmatic patients (4,32). Preliminary data from the Lung Health Study have provided evidence that the use of an inhaled anticholinergic bronchodilator appears not to in uence the long-term decline of FEV 1 in middle-aged smokers with mild airway obstruction, whereas an intensive smoking cessation program signi cantly reduced the decline (35). We conclude that cold air-associated dyspnoea aggravation was clearly related to the severity of airways obstruction, whereas chronic cough and phlegm production showed an inverse relationship. Factors other than smoking may also play an important role in the development of chronic bronchitis and COPD in women. References 1. Hoidal JR. Pathogenesis of chronic bronchitis. Semin Respir Infect 1994; 9: 8±12. 2. Petty TL. Symposium summary: We must do better. Chest 1990; 97(Suppl): 33S. 3. Burrows B, Bloom JW, Traver GA, Cline MG. The course and prognosis of di erent forms of chronic airways obstruction in a sample from the general population. N Engl J Med 1987; 317: 1309±1314. 4. Woolcock AJ, Anderson SD, Peat JK, et al. Characteristics of bronchial hyperresponsiveness in chronic obstructive pulmonary disease and in asthma. Am Rev Respir Dis 1991; 143: 1438±1442. 5. Hole DJ, Watt GCM, Davey-Smith G, Hart CL, Gillis CR, Hawthorne VM. Impaired lung function and mortality risk in men and women: ndings from the Renfrew and Paisley prospective population study. Br Med J 1996; 313: 711±715. 6. Celli BR, Snider GL, He ner J, et al. Standards for the diagnosis and care of patients with chronic obstructive disease. The o cial statement of the American Thoracic Society. Am J Respir Crit Care Med 1995; 152: S77±S120. 7. Strachan DP. Ventilatory function, height, and mortality among lifelong non-smokers. J Epidemiol Comm Health 1992; 46: 66±70. 8. Peat JK, Woolcock AJ, Cullen K. Decline of lung function and development of chronic air ow limitation: a longitudinal study of non-smokers and smokers in Busselton, Western Australia. Thorax 1990; 45: 32±37. 9. Siafakas NM, Vermeire P, Pride NB, et al. ERS Consensus Statement. Optimal assessment and management of chronic obstructive pulmonary disease (COPD). Eur Respir J 1995; 8: 1398±1420. 10. Medical Research Council. De nition and classi cation of chronic bronchitis, clinical and epidemiological purposes: a report to the Medical Research Council by their committee on the etiology of chronic bronchitis. Lancet 1965; i: 775±780. 11. Rose GA, Blackburn H, Gillium RF, Prineas RJ. Cardiovascular survey methods. WHO Monograph Series No. 56. Geneva: World Health Organization, 1982: 149±172. 12. Ciba Guest Symposium. Terminology, de nitions, and classi cation of chronic pulmonary emphysema and related conditions. A report of the conclusions of a Ciba Guest Symposium. Thorax 1959; 14: 286±299. 13. WHO memorandum. Epidemiology of chronic nonspeci c respiratory diseases. Bull World Health Organization 1975; 52: 251±60. 14. Thurlbeck WM. Chronic air ow obstruction in lung disease. Philadelphia, PA: WB Saunders, 1976. 15. Thurlbeck WM. Pathology of chronic air ow obstruction. Chest 1990; 97(Suppl.): 6S±10S. 16. Isoaho R, Puolijoki H, Huhti E, KivelaÈ S-L, Laippala P, Tala E. Prevalence of chronic obstructive pulmonary disease in elderly Finns. Respir Med 1994; 88: 571±580. 17. Bakke PS, Baste V, Hanoa R, Gulsvik A. Prevalence of obstructive lung disease in a general population: relation to occupational title and exposure to some airborne agents. Thorax 1991; 46: 863±870. 18. Lange P, Groth S, Nyboe J, et al. Chronic obstructive lung disease in Copenhagen: cross-sectional epidemiological aspects. J Intern Med 1989; 226: 25±32. 19. Olofson J, Skoogh B-E, Bake B, SvaÈ rdsudd K. Mortality related to smoking habits, respiratory symptoms and lung function. Eur J Respir Dis 1987; 71: 69±76. 20. Ebi-Kryston KL. Respiratory symptoms and pulmonary function as predictors of 10-year mortality from respiratory disease, cardiovascular disease, andall causes in the Whitehall Study. J Clin Epidemiol 1988; 41: 251±260. 21. Crapo RA. Pulmonary-function testing. N Engl J Med 1994; 331: 25±30.
RESPIRATORY SYMPTOMS AND SEVERITY OF AIRWAY OBSTRUCTION 363 22. LundbaÈ ck B, Stjernberg N, NystroÈ m L, LundbaÈ ck K, LindstroÈ m M, Rosenhall L. An interview study to estimate prevalence of asthma and chronic bronchitis. Eur J Epidemiol 1993; 9: 123±133. 23. Chronic bronchitis and chronic obstructive pulmonary disease. National guidelines for prevention and treatment 1998±2007. Helsinki: Ministry of Social A airs and Health, 1998; 16. 24. von Hertzen L, AlakaÈ rppaè H, Koskinen R, et al. Chlamydia pneumoniae infection in patients with chronic obstructive pulmonary disease. Epidemiol Infect 1997; 118: 155±164. 25. Matsuse T, Hayashi S, Kuwano K, Keunecke H, Je eries WA, Hogg JC. Latent adenoviral infection in the pathogenesis of chronic airways obstruction. Am Rev Respir Dis 1992; 148: 177±184. 26. Pearson MG, Calverley PM. Clinical and laboratory assessment. In: Calverley P, Pride N, eds. Chronic obstructive pulmonary disease. London: Chapman & Hall, 1995: 309±349. 27. Linde n M, Rasmussen JB, Piitulainen E, et al. Airway in ammation in smokers with nonobstructive and obstructive chronic bronchitis. Am Rev Respir Dis 1993; 148: 1226±1232. 28. Fletcher C, Peto R, Tinker C, Speizer FE. The natural history of chronic bronchitis and emphysema. Oxford: Oxford University Press, 1976. 29. Peto R, Speizer FE, Cochrane AL, et al. The relevance in adults of air- ow obstruction, but not mucus hypersecretion, to mortality from chronic lung disease. Am Rev Respir Dis 1983; 128: 491±500. 30. Vestbo J, Prescott E, Lange P. Association of chronic mucus hypersecretion with FEV 1 decline and chronic obstructive pulmonary disease morbidity. Am J Respir Crit Care Med 1996; 153: 1530±1535. 31. Levin JL, Gri th DE. Occupational chronic bronchitis: does it mean anything? Seminars Respir Infect 1994; 9: 23±30. 32. Yan K, Salome CM, Woolcock AJ. Prevalence and nature of bronchial hyperresponsiveness in subjects with chronic obstructive pulmonary disease. Am Rev Respir Dis 1985; 132: 25±29. 33. Peat JK, Salome CM, Berry G, Woolcock AJ. Relation of dose-response slope to respiratory symptoms and lung function in a population study of adults living in Busselton, Western Australia. Am Rev Respir Dis 1992; 146: 860±65. 34. Taylor RG, Joyce H, Gross E, Holland F, Pride NB. Bronchial reactivity to inhaled histamine and annual rate of decline in FEV 1 in male smokers and exsmokers. Thorax 1985; 40: 9±16. 35. Anthonisen NR, Connett JE, Kiley JP, et al. E ects of smoking intervention and the use of an inhaled anticholinergic bronchodilator on the rate of decline of FEV 1. The Lung Health Study. JAMA 1994; 272: 1497±1505.