Published on 25.07.17 in Vol 6, No 7 (2017): July
Cross-Sectional Study of Chronic Obstructive Pulmonary Disease Prevalence Among Smokers, Ex-Smokers, and Never-Smokers in Almaty, Kazakhstan: Study Protocol
Background: Chronic obstructive pulmonary disease (COPD) is significantly underdiagnosed in Kazakhstan, and there is no previously conducted study on COPD prevalence in the country.
Objective: The purpose of this study is to assess the prevalence of COPD among individuals aged 40 to 59 years based on results of spirometry before and after bronchodilator, presence of structural changes in the lungs (emphysema, inflammatory changes, and thickening of the walls of the large and small airways) detected by computer tomography, and the symptoms of COPD. The study has 3 study groups: smokers of conventional cigarettes, those who had quit smoking 1 to 5 years ago, and those who haven’t smoked cigarettes.
Methods: This is an observational study with a cross-sectional design among individuals aged 40 to 59 years in Almaty, Kazakhstan. The sample of 900 individuals of both sexes contains 500 smokers, 200 ex-smokers, and 200 never-smokers. Study measures include spirometry, chest computed tomography, electrocardiography, physical exams, laboratory testing of serum, anthropometry, and 6-minute walk test. Data are collected by computer-assisted personal interviewing with tablets. The questionnaire was designed to explore possible COPD risk factors including history of smoking, current smoking, level of smoking exposure (in pack-years), passive smoking, occupational and environmental hazards, and covariates: age, gender, ethnicity, education, occupation, and self-reported morbidity. COPD Assessment Test (CAT) is used to collect information about COPD symptoms.
Results: We have completed the participant recruitment and study procedures. Currently, we are working on data processing and data analysis. The authors anticipate the preliminary results should be available by September 2017. Study results will be published in peer-reviewed scientific journals.
Conclusions: This is the first study in Kazakhstan that assesses prevalence of COPD and its comorbidities in the adult population aged 40 to 59 years. The results of the study will be useful for improving COPD preventive measures, better COPD screening, identification, and registration. Findings of the study will also contribute to global knowledge on the epidemiology of COPD.
Trial Registration: ClinicalTrials.gov NCT02926534; https://clinicaltrials.gov/ct2/show/NCT02926534 (Archived by WebCite at http://www.webcitation.org/6rjwGsPOZ)
JMIR Res Protoc 2017;6(7):e143
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Chronic obstructive pulmonary disease (COPD) is the fourth leading cause of death worldwide . The number of affected individuals and deaths from COPD are expected to increase as the population ages [ ]. In Russia, the largest neighboring country of Kazakhstan, the prevalence of symptomatic COPD in the adult population was estimated to be 15.3% [ ]. An estimated 1.4 million individuals in Kazakhstan may be affected by COPD. This estimate is based on studies that have been conducted in other countries in the World Health Organization European Region [ ] but not in Kazakhstan, because a study on the prevalence of COPD has not been conducted in the country yet. COPD is significantly underdiagnosed in Kazakhstan. In 2013, the rate of reported COPD cases was 315.9 per 100,000 or around 53,000 registered cases of COPD [ ]. A better understanding of the epidemiology and social and other determinants of the disease is needed in order to recognize the true magnitude of the problem and develop effective treatments and prevention strategies.
Various criteria for COPD have been used in population-based studies. The most common criterion is airflow obstruction detected by spirometry testing, defined as a postbronchodilator ratio of forced expiratory volume in 1 second (FEV1) to forced vital capacity (FVC) less than 0.7 or 70% . This criterion is simple to implement and widely used in epidemiological surveys. However, COPD prevalence based on this could be slightly biased—overestimated in old subjects and underestimated in younger ones [ ]. For this reason, the fifth percentile of the FEV1/FVC ratio or the lower limit of normal distribution of the FEV1/FVC ratio defined for specific age-gender group is also recommended for use in epidemiological studies [ ].
Respiratory symptoms  and physical examination [ ] were frequently used to evaluate COPD prevalence. However, collecting such data is more important for establishing the clinical diagnosis of COPD [ ]. The specific symptoms of COPD include progressive dyspnea, cough, and sputum production [ ]. The COPD Assessment Test (CAT) was specially designed to measure how COPD symptoms lead to health status impairment. The test is derived from 8 items, and the score varies from 0 to 40. The cut-off point for the CAT is 10, after which regular treatment for symptoms is recommended [ ]. Although a physical examination is rarely used in COPD diagnosis, particularly in detecting mild to moderate COPD, thoracic examination of patients with severe disease can usually reveal the following signs: hyperinflation, wheezing, diffusely decreased breath sounds, hyperresonance on percussion, and prolonged expiration [ ].
Chest computed tomography (CT) scan is recommended for subjects with airflow limitation and signs and symptoms suggestive of COPD for making an accurate diagnosis of COPD to exclude other conditions . CT scan also helps to separate COPD patients into 2 main phenotypes, emphysema and small airway disease [ ]. CT images can be visually assessed by qualified observers to describe patterns of altered lung structure or quantified for assessment of the extent of emphysema, gas trapping, and airway abnormality [ ]. Some studies suggested that severity of emphysema detected by CT scan is associated with greater lung function decline even if airway obstruction is not currently presented [ , ]. As a result, CT-detected emphysema may predict future development of airflow obstruction [ , ].
Tobacco smoking, occupational and environmental exposures including workplace dusts and chemicals, and smoke from home cooking and heating fuels are the main risk factors for COPD . In addition, advanced age, chronic respiratory infections such as tuberculosis, low socioeconomic status, and being underweight may influence COPD development [ , ]. Genetic predisposition also plays an important role in COPD development. Originally described more than 50 years ago, α1-antitrypsin deficiency may cause COPD and accounts for 1% to 2% of all COPD cases. There are other genome variants currently being investigated as candidates for COPD genes, but only the Z variant of α1-antitrypsin is accepted as a COPD gene at the present time [ ].
Comorbidities are frequently found in persons with COPD. Some of them have risk factors, which are the same as for COPD, particularly tobacco smoking and aging. Moreover, systemic inflammation and chronic hypoxia present in COPD patients may cause other health-related conditions. Common comorbidities include heart disease, lung cancer, osteoporosis, metabolic syndrome and diabetes, anemia, anxiety, cognitive decline, and sleep disorders [, ]. Specific comorbidities increase mortality and poor outcome in COPD, so management of main comorbidities has been included to COPD guidelines [ ].
The aim of the study is to assess the prevalence of COPD among smokers, ex-smokers, and never-smokers aged 40 to 59 years based on pulmonary function assessment (spirometry), structural changes (emphysema and large and small airway inflammation with thickening) identified by high-resolution CT, COPD symptoms, and exercise limitations. In addition, the study objectives include comparing the prevalence of health conditions considered as COPD comorbidities (heart disease, hypertension, metabolic syndrome, diabetes mellitus) in 3 study groups and their interaction with COPD.
This is an observational study with a cross-sectional design to assess the prevalence of COPD in Almaty, Kazakhstan, among individuals aged 40 to 59 years based on results of spirometry, the presence of structural changes in the lungs, and symptoms of COPD.
The study population is 3 groups of male and female residents of Almaty, the largest city in Kazakhstan, with a population of 1.7 million people, 9% of whom are aged 40 to 59 years. Members of the first group include current smokers with more than a 10 pack-year history of smoking (smokers). The second group comprises individuals who quit smoking from 1 to 5 years ago and have more than a 10 pack-year history of smoking (ex-smokers). The third group comprises persons who have never smoked regularly (ie, smoked less than 100 cigarettes in their lifetime) (never-smokers).
We recruited individuals who are 40 years of age or older because most people are at least 40 years old when the symptoms of COPD first appear . The same age limit is selected for many COPD prevalence studies [ - ]. The upper age was set at 59 years to avoid survival bias [ ] possibly leading to underestimating the effects of risk factors on COPD. We have taken into account that the life expectancy at birth among males was only 66 years in Kazakhstan in 2015 [ ].
Inclusion and Exclusion Criteria
Male and female participants aged 40 to 59 years who have a 10 pack-year and more of smoking history (for smokers and ex-smokers) or fewer than 100 cigarettes in their lifetime (for never-smokers) and are able to provide informed consent can be included in this study.
- Fever (37°C or higher) at the time of the visit or during the 2 weeks preceding the visit
- Legally incapable
- Chronic infectious and noninfectious lung disease except asthma (eg, pulmonary fibrosis, bronchiectasis, cystic fibrosis, tuberculosis)
- Resection of at least one lobe (or performing procedures to reduce lung volume)
- Any cancer; receiving a course of radiation or chemotherapy at the time of the visit
- Suspected lung cancer (presence of significant lung neoplasm)
- Presence of metal in the chest
- Ophthalmic surgery within the last 12 months prior to the visit
- Myocardial infarction or other form of acute or chronic coronary insufficiency or cardiac arrhythmia diagnosed at least 6 months prior to the visit
- Myocardial infarction or other form of acute or chronic coronary insufficiency or cardiac arrhythmia for which an individual regularly receives medication
- Severely elevated blood pressure (equal to or greater than a systolic 180 or diastolic of 100)
- History of cerebrovascular accident
- Thoracic or abdominal surgery within the last 6 months
- Contraindications to use salbutamol or its analogs
- CT scan or other research using ionizing radiation within the last 6 months
According to the Burden of Obstructive Lung Disease (BOLD) protocol, a minimal sample size of 600 is recommended to achieve an acceptable level of precision for estimating COPD prevalence . Our goal is for a sample size of 900 including 500 smokers, 200 ex-smokers, and 200 never-smokers. We have used the National Health and Nutrition Examination Surveys data to assume COPD prevalence in these 3 groups [ ]. The sample size of 500 allows for achieving the precision of 3.5% with the expected prevalence of obstructive impairment of 20%. The sample size of 200 and the expected prevalence of pulmonary obstruction of 10% and 2% among ex-smokers and never-smokers, respectively, provides sample estimates with 4.2% and 1.9% precision, respectively [ ].
The 3 study groups are planned to have the same gender and age distribution by implementing age-gender quota to eliminate age and gender potential confounding effect to the associations between smoking status and outcomes.
It was shown that the sample characteristics depend on recruitment method used . To recruit study participants, active and passive approaches are used. Participants are recruited by using personal networks of investigators and persons who are already participating in the study (snowball), placing an advertisement of the study in social media (Facebook) targeting those individuals who are potentially eligible to participate (live in Almaty, specific age group), and meeting with the owners and managerial staff of several large companies located in Almaty to explain the benefits of participation in the study. Employees of these companies who are potentially eligible to participate in the study are contacted by phone calls.
The study flow is shown in. Participants are expected to attend 2 to 3 visits for the study, for a total of about 3 hours. Completing study procedures for each participant, including sharing the study results with the participant, is expected to take up to 2 weeks.
Spirometry is performed by trained investigators, with 3 technically satisfactory maneuvers performed by each study participant. The largest value of FEV1 and the respective value FVC are selected to calculate ratio of FEV1 to FVC. The CardioTouch 3000-S (BiTech Medical Corp), a 12-lead resting electrocardiogram (ECG) machine with a spirometer with a measuring accuracy that complies with American Thoracic Society requirements , is used to perform lung function tests. Calibration of the spirometer was performed every day before using it. A 3-L syringe was pumped through to check that accuracy did not exceed a tolerance of 3% [ ].
Study subjects undergo 64-channel CT scans of the chest (Philips Brilliance CT 64). Subjects with restrictive (FEV1/FVC from 70% to 80%) and obstructive (FEV1/FVC less than 70%) lung diseases or signs and symptoms of COPD found during the physical examination and survey undergo inspiratory-expiratory CT scans obtained at the following settings: detector collimation 0.6-0.75 mm, 0.625-0.9 mm reconstructed slice thickness, 0.45-0.625 mm slice interval, 120 kV, 200 (inspiratory) and 50 (expiratory) mAs. Other subjects have only inspiratory CT scans: 0.8 mm reconstructed slice thickness, 0.4 mm slice interval, smooth reconstruction algorithm iDose 7, matrix size 512×512, range = –500 to 1500, 120 kV, 40 mAs .
CT scans are evaluated by 3 independent qualified observers to produce semiquantified measures that characterize the extent of emphysema, severity of bronchial dilatation, traction bronchiectasis, bronchial wall thickening, and small airway disease. We use the Bhala scoring system  modified by Tulek at al [ ]. The kappa test will be used to evaluate interrater reliability of visual CT scan analysis. The median score by 3 observers will be recorded for each participant.
A standard 12-lead ECG is performed with the CardioTouch 3000-S for each study subject by employing strictly standardized procedures. Research staff members were trained to properly place electrodes. At least 4 cardiac cycles are taken from each of 12 leads. The machine runs at 50 mm/sec. The following ECG parameters are evaluated by a trained clinical researcher: waves and complexes, presence and description of ECG abnormalities including pathologic q-waves, ST elevation, ST depression, T-wave inversion, hypertrophy, QRS axis deviation, block, and arrhythmia. ECGs were visually inspected for technical errors and were interpreted by a qualified cardiologist. The prevalence of specific ECG abnormalities as well as grouped abnormalities will be reported for each study group. Associations between COPD and ECG abnormalities, crude and adjusted by sex, age, and smoking status, will be measured and presented.
Clinical investigators were trained to conduct the pulmonary (percussion and inspection) exam and technique for listening to second heart sounds. Two Stanford Medicine 25 modules were used as study materials in hands-on sessions [, ]. The prevalence of individual pathological findings will be presented for each study group. Associations between pathological findings from 2 exams and COPD will be evaluated.
Anthropometry measures include height, weight, waist circumference, heart rate, blood pressure, and pulse oximetry.
Six-Minute Walk Test
All study subjects will take a 6-minute walk test to evaluate functional exercise capacity. Investigators assess whether contraindication exists or not. Absolute contraindications are unstable angina and myocardial infarction during the previous month. Relative contraindications are blood pressure more than 180/100 mm Hg and a resting heart rate of more than 120 beats per minute . Subjects with any of the contraindications are referred to the clinical coordinator for a decision about the conduct of the test. Posttest dyspnea is measured using the Borg scale [ ].
Serum from each participant is tested for blood cholesterol level, high-density lipoprotein (HDL), low-density lipoprotein (LDL)), triglycerides, C-reactive protein, fibrinogen, glucose, hepatitis B and C IgM and IgG antigens and antibodies, alanine aminotransferase (ALT) and aspartate aminotransferase (AST) liver enzymes, and α1-antitrypsin.
The questionnaire was designed to collect data on possible COPD risk factors including history of smoking; current smoking; level of smoking exposure (in pack-year); passive smoking; and occupational and environmental hazards including dusts, chemicals, and indoor fuel pollution. The questionnaire contains the following covariates: age, gender, ethnicity, education, occupation, and self-reported morbidity. CAT is used to collect Information about COPD symptoms. The test was designed and validated for use in routine clinical practice to evaluate the health status of patients with COPD . Computer-assisted personal interviewing (CAPI) with tablets has been implemented to collect, store, and transmit data related to a personal survey interview.
The questionnaire was piloted by interviewing 7 testers—3 smokers, 2 ex-smokers, and 2 never-smokers. After completing pilot interviews, the testers were asked to answer specific questions and then provide comments and suggestions on the whole questionnaire. The questions that were not clear enough were identified and have been improved.
Data from all CAPI devices will be exported to one database, and R version 3.3.1 (The R Foundation) will be used for data analysis. Descriptive analyses will be performed using mean, median, interquartile interval, and standard deviation for quantitative variables and frequency tables for categorical variables. Depending on the nature of outcome and exposure variables, type of data distribution, and the sample size, bivariate comparisons will be made by the following tests: chi-square test, Fisher’s exact test, analysis of variance, t test, and the Mann-Whitney test.
A multivariable analysis (generalized linear models) will be conducted to control for confounding. Presence of effect modification/interaction terms will be explored. An alpha <.05 will be considered significant. To construct the optimal model, backward elimination will be used. The full models will contain all independent effects and some important interactions. Mediators (variables that lie on the causal pathway between exposure and outcome) will not be included in the model. To avoid multicollinearity, we will examine the tolerance for each independent variable. If the tolerance value is less than 0.1, we will omit a variable from the analysis. The optimal model will be defined based on the Akaike Information Criterion. Model diagnostic plots will be generated to test model assumptions (eg, normality of deviance residuals).
The National Central Ethics Committee under the Ministry of Health and Social Development in the Republic of Kazakhstan approved this study on August 19, 2016. The study has been registered at ClinicalTrials.gov [NCT02926534].
We have completed the participant recruitment and study procedures. Currently, we are working on data processing and data analysis. The authors anticipate the preliminary results should be available by September 2017. Study results will be published in peer-reviewed scientific journals.
To the best of our knowledge, this is the first study in Kazakhstan that assesses COPD prevalence in the general population aged 40 to 59 years, specifically smokers, ex-smokers, and never-smokers. The study also aims to investigate COPD comorbidities and their interaction with COPD. Improving COPD preventive measures, COPD screening, identification, and registration requires obtaining this epidemiological information. Study strengths include its relatively large sample size and collection of comprehensive medical, behavioral, and other health-related data from each study participant.
However, there remain some limitations. First, the study is observational. Thus, the possibility of unidentified or unmeasured confounders exists. We are going to conduct the sensitivity analysis to assess a covariate that could eliminate the effect of smoking on COPD. Second, the study is cross-sectional, and the time when COPD occurred cannot be identified. The values of potential confounders measured in the study could differ from ones when symptoms of COPD first appeared and could be diagnosed. As a result, causal inferences cannot be made. Third, the study includes many components to be measured, which makes it impossible to employ probability sampling to select participants. The main risk of nonprobability sampling is that the distribution of important covariates in the sample will differ significantly from their distribution in the study population. We employ quota sampling to set quotas for gender and age, 2 important covariates for COPD, to balance them in the sample. In addition, we measure all known important covariates or confounders to make the desired adjustments in our data analysis. Fourth, the study is conducted in one city, Almaty, which reduces the generalizability of the study results to the country population. Finally, we expect some measurement bias that arises from errors in the data collection. For example, participants could avoid socially undesirable answers. To reduce the latter bias, all data collection procedures were tested and the research staff members were trained.
This study is supported with resources and the use of facilities at Kazakhstan Academy оf Preventive Medicine, the HealthCity Clinic, and Synergy Group Kazakhstan. The project is partially funded by a grant from Philip Morris International (IIS.PMI.2016.001). This funder had no role in collection, analysis, or interpretation of data or in writing the manuscript.
The study was designed by AS, DS, and BZ. AS and BZ drafted the manuscript. All authors critically revised the manuscript. All authors read and approved the final manuscript.
Conflicts of Interest
- Lozano R, Naghavi M, Foreman K, Lim S, Shibuya K, Aboyans V, et al. Global and regional mortality from 235 causes of death for 20 age groups in 1990 and 2010: a systematic analysis for the Global Burden of Disease Study 2010. Lancet 2012 Dec 15;380(9859):2095-2128. [CrossRef] [Medline]
- Murray CJ, Lopez AD. Alternative projections of mortality and disability by cause 1990-2020: Global Burden of Disease Study. Lancet 1997 May 24;349(9064):1498-1504. [CrossRef] [Medline]
- Chuchalin AG, Khaltaev N, Antonov NS, Galkin DV, Manakov LG, Antonini P, et al. Chronic respiratory diseases and risk factors in 12 regions of the Russian Federation. Int J Chron Obstruct Pulmon Dis 2014;9:963-974 [FREE Full text] [CrossRef] [Medline]
- Adeloye D, Chua S, Lee C, Basquill C, Papana A, Theodoratou E, et al. Global and regional estimates of COPD prevalence: systematic review and meta-analysis. J Glob Health 2015 Dec;5(2):020415 [FREE Full text] [CrossRef] [Medline]
- National Center for the Problems of Forming the Healthy Lifestyle: press release. URL: http://www.hls.kz/rus/press-releases_1_61 [accessed 2017-07-06] [WebCite Cache]
- Global Initiative for Chronic Obstructive Lung Disease. Global strategy for the diagnosis, management, and prevention of COPD. URL: http://goldcopd.org/global-strategy-diagnosis-management-prevention-copd-2016/ [accessed 2017-01-25] [WebCite Cache]
- Swanney MP, Ruppel G, Enright PL, Pedersen OF, Crapo RO, Miller MR, et al. Using the lower limit of normal for the FEV1/FVC ratio reduces the misclassification of airway obstruction. Thorax 2008 Dec;63(12):1046-1051. [CrossRef] [Medline]
- Bakke PS, Rönmark E, Eagan T, Pistelli F, Annesi-Maesano I, Maly M, et al. Recommendations for epidemiological studies on COPD. Eur Respir J 2011 Dec;38(6):1261-1277 [FREE Full text] [CrossRef] [Medline]
- Lundbäck B, Stjernberg N, Nyström L, Forsberg B, Lindström M, Lundbäck K, et al. Epidemiology of respiratory symptoms, lung function and important determinants. Report from the Obstructive Lung Disease in Northern Sweden Project. Tuber Lung Dis 1994 Apr;75(2):116-126. [CrossRef] [Medline]
- Bakke P, Eide GE, Hanoa R, Gulsvik A. Occupational dust or gas exposure and prevalences of respiratory symptoms and asthma in a general population. Eur Respir J 1991 Mar;4(3):273-278. [Medline]
- Koff RS. Fundamentals of lung auscultation. N Engl J Med 2014 May 22;370(21):2053. [CrossRef] [Medline]
- Make BJ, Martinez FJ. Assessment of patients with chronic obstructive pulmonary disease. Proc Am Thorac Soc 2008 Dec 15;5(9):884-890 [FREE Full text] [CrossRef] [Medline]
- Pistolesi M, Camiciottoli G, Paoletti M, Marmai C, Lavorini F, Meoni E, et al. Identification of a predominant COPD phenotype in clinical practice. Respir Med 2008 Mar;102(3):367-376 [FREE Full text] [CrossRef] [Medline]
- Lynch DA, Austin JHM, Hogg JC, Grenier PA, Kauczor H, Bankier AA, et al. CT-definable subtypes of chronic obstructive pulmonary disease: a statement of the Fleischner Society. Radiology 2015 Oct;277(1):192-205 [FREE Full text] [CrossRef] [Medline]
- Mohamed HFAA, Zanen P, Gietema H, Kruitwagen CLJJ, Isgum I, Mol C, et al. CT-quantified emphysema in male heavy smokers: association with lung function decline. Thorax 2011 Sep;66(9):782-787. [CrossRef] [Medline]
- Koo H, Jin KN, Kim DK, Chung HS, Lee C. Association of incidental emphysema with annual lung function decline and future development of airflow limitation. Int J Chron Obstruct Pulmon Dis 2016;11:161-166 [FREE Full text] [CrossRef] [Medline]
- Sin DD, Leipsic J, Man SFP. CT in COPD: just a pretty picture or really worth a thousand words (or dollars)? Thorax 2011 Sep;66(9):741-742. [CrossRef] [Medline]
- Rosenberg SR, Kalhan R, Mannino DM. Epidemiology of chronic obstructive pulmonary disease: prevalence, morbidity, mortality, and risk factors. Semin Respir Crit Care Med 2015 Aug;36(4):457-469. [CrossRef] [Medline]
- Lee SJ, Kim SW, Kong KA, Ryu YJ, Lee JH, Chang JH. Risk factors for chronic obstructive pulmonary disease among never-smokers in Korea. Int J Chron Obstruct Pulmon Dis 2015;10:497-506 [FREE Full text] [CrossRef] [Medline]
- Berndt A, Leme AS, Shapiro SD. Emerging genetics of COPD. EMBO Mol Med 2012 Nov;4(11):1144-1155 [FREE Full text] [CrossRef] [Medline]
- Cavaillès A, Brinchault-Rabin G, Dixmier A, Goupil F, Gut-Gobert C, Marchand-Adam S, et al. Comorbidities of COPD. Eur Respir Rev 2013 Dec;22(130):454-475 [FREE Full text] [CrossRef] [Medline]
- Chatila WM, Thomashow BM, Minai OA, Criner GJ, Make BJ. Comorbidities in chronic obstructive pulmonary disease. Proc Am Thorac Soc 2008 May 01;5(4):549-555 [FREE Full text] [CrossRef] [Medline]
- Shavelle RM, Paculdo DR, Kush SJ, Mannino DM, Strauss DJ. Life expectancy and years of life lost in chronic obstructive pulmonary disease: findings from the NHANES III Follow-up Study. Int J Chron Obstruct Pulmon Dis 2009;4:137-148 [FREE Full text] [Medline]
- Daldoul H, Denguezli M, Jithoo A, Gnatiuc L, Buist S, Burney P, et al. Prevalence of COPD and tobacco smoking in Tunisia—results from the BOLD study. Int J Environ Res Public Health 2013 Dec 17;10(12):7257-7271 [FREE Full text] [CrossRef] [Medline]
- Alhamad EH, Alorainy HS, Lababidi H, Al-Hajjaj MS. The prevalence of chronic obstructive pulmonary disease in Riyadh, Saudi Arabia: a BOLD study. Int J Tuberc Lung Dis 2015 Oct;19(10):1252-1257. [CrossRef] [Medline]
- Danielsson P, Ólafsdóttir IS, Benediktsdóttir B, Gíslason T, Janson C. The prevalence of chronic obstructive pulmonary disease in Uppsala, Sweden—the Burden of Obstructive Lung Disease (BOLD) study: cross-sectional population-based study. Clin Respir J 2012 Apr;6(2):120-127. [CrossRef] [Medline]
- Rothman RJ, Greenland S, Lash TL. Modern Epidemiology. Third Edition. Philadelphia: Lippincott-Williams & Wilkins Publishers; 2008.
- World Health Organization. The WHO country health profile of Kazakhstan. URL: http://www.who.int/countries/kaz/en/ [accessed 2017-05-14] [WebCite Cache]
- Buist AS, Vollmer WM, Sullivan SD, Weiss KB, Lee TA, Menezes AMB, et al. The Burden of Obstructive Lung Disease Initiative (BOLD): rationale and design. COPD 2005 Jun;2(2):277-283. [Medline]
- Ford ES, Mannino DM, Wheaton AG, Giles WH, Presley-Cantrell L, Croft JB. Trends in the prevalence of obstructive and restrictive lung function among adults in the United States: findings from the National Health and Nutrition Examination surveys from 1988-1994 to 2007-2010. Chest 2013 May;143(5):1395-1406 [FREE Full text] [CrossRef] [Medline]
- Lohr SL. Sampling: Design and Analysis. 2nd Edition. Boston: Cengage Learning; 2010.
- Hoving C, Mudde AN. Effect of recruitment method and setting on the composition of samples consisting of adult smokers. Patient Educ Couns 2007 Jan;65(1):79-86. [CrossRef] [Medline]
- Miller MR, Hankinson J, Brusasco V, Burgos F, Casaburi R, Coates A, et al. Standardisation of spirometry. Eur Respir J 2005 Aug;26(2):319-338 [FREE Full text] [CrossRef] [Medline]
- Beigelman-Aubry C. Advanced chest imaging. URL: http://clinical.netforum.healthcare.philips.com/us_en/Explore/Abstracts/CT/Advanced-chest-imaging [accessed 2017-07-06] [WebCite Cache]
- Bhalla M, Turcios N, Aponte V, Jenkins M, Leitman BS, McCauley DI, et al. Cystic fibrosis: scoring system with thin-section CT. Radiology 1991 Jun;179(3):783-788. [CrossRef] [Medline]
- Tulek B, Kivrak AS, Ozbek S, Kanat F, Suerdem M. Phenotyping of chronic obstructive pulmonary disease using the modified Bhalla scoring system for high-resolution computed tomography. Can Respir J 2013;20(2):91-96 [FREE Full text] [Medline]
- Stanford Medicine 25. Pulmonary exam: percussion and inspection URL: http://stanfordmedicine25.stanford.edu/the25/pulmonary.html [accessed 2017-07-06] [WebCite Cache]
- Stanford Medicine 25. Cardiac second sounds URL: http://stanfordmedicine25.stanford.edu/the25/cardiac.html [accessed 2017-01-25] [WebCite Cache]
- American Thoracic Society. ATS statement: guidelines for the six-minute walk test. Am J Respir Crit Care Med 2002 Jul 1;166(1):111-117. [CrossRef] [Medline]
- Mahler DA, Horowitz MB. Perception of breathlessness during exercise in patients with respiratory disease. Med Sci Sports Exerc 1994 Sep;26(9):1078-1081. [Medline]
- Jones PW, Harding G, Berry P, Wiklund I, Chen W, Kline LN. Development and first validation of the COPD Assessment Test. Eur Respir J 2009 Sep;34(3):648-654 [FREE Full text] [CrossRef] [Medline]
|BOLD: Burden of Obstructive Lung Disease|
|CAT: COPD Assessment Test|
|CAPI: computer-assisted personal interviewing|
|COPD: chronic obstructive pulmonary disease|
|CT: computed tomography|
|FEV1: forced expiratory volume in 1 second|
|FVC: forced vital capacity|
Edited by G Eysenbach; submitted 27.01.17; peer-reviewed by F Pourmalek; comments to author 20.03.17; revised version received 16.05.17; accepted 23.05.17; published 25.07.17
©Almaz Sharman, Baurzhan Zhussupov, Dana Sharman, Assel Stambekova, Sattar Yeraliyev. Originally published in JMIR Research Protocols (http://www.researchprotocols.org), 25.07.2017.
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