COPD and chronic bronchitis risk of indoor air pollution from solid fuel: a systematic review and meta-analysis - indoor air cleaner

More than half of the world's people are exposed to the smoke generated by solid fuel burning every day.
Chronic pulmonary disease (COPD)
Is one of the major contributors to the global burden of disease, possibly due to exposure to biomass smoke.
However, studies of biomass exposure and chronic lung obstruction have shown a wide range of impacts.
The purpose of this systematic review is to quantify the effect of biomass smoke on the development of chronic lung obstruction and to identify the causes of the difference in the size of the reported effects.
Methods a systematic review of studies with sufficient statistical capacity to calculate the health risk of using solid fuel for chronic lung obstruction followed standardized criteria for the diagnosis of chronic lung obstruction and to deal with mixed factors.
These results are aggregated by fuel type and country, using a random effect model for aggregate estimation.
Publication bias was also estimated.
Results The use of solid fuel and chronic lung obstruction (OR=2. 80, 95% CI 1. 85 to 4. 0)
And chronic branchOR=2. 32, 95% CI 1. 92 to 2. 80).
Summary estimates of different types of fuels indicate that exposure to wood smoke during household work is more likely to develop into chronic lung and chronic bronchitis than other fuels.
Conclusion despite the heterogeneity in selected studies, exposure to solid fuel smoke is always associated with chronic lung and bronchitis.
Efforts should be made to reduce access to solid fuels, using clean fuels or relatively clean technologies when doing home work.
Search strategies using Medline (1980–2009)
, Cochrane database, Google Scholar (
Advanced Google search)
Library and Information Network knowledge base of the World Health Organization (WHOLIS)
We used "or" and "and" as combined terms for exposure and results, and conducted a literature search on the use of chronic pulmonary obstruction, chronic bronchitis, and biomass or solid fuels.
The search terms used are summarized in supplementary table s1.
In Supplementary Table S1, the number of hits and steps to search for literature from MEDLINE are given, and the combination is given in Supplementary Table s2.
The same search terms are used by other search engines and databases.
References in each identified paper are screened out for any article not identified in the original search.
The aim was to analyze the studies, which took into account the chronic obstruction lung as defined by the lung activity assay, whereas, based on the questionnaire response, the study considered chronic bronchitis.
Selection of studies to be included in the inclusion criteria of meta-papers
The analysis is given in Box 1.
Figure 1 gives the details of the review process and a flow chart of the studies included and excluded.
The method originally incorporated into the study was intended to expand the scope.
Instead of using standard quality tools, we have developed a list of key information that requires a presence in each study.
Extract information from 63 papers using predefined tables, 23 of which (10 for COPD (table 1)
, 11 cases of chronic bronchitis, 2 cases each ,(table 2))
Meet the inclusion criteria and in meta-analysis.
Studies that did not have an appropriate comparison group were discarded.
Box 1 only systematically reviews the inclusion criteria of English.
The paper contains the original data and is completelength peer-
Cohort, case-control, or cross-examination report
Segmentation research. Data for a non-
Exposed comparison groups were provided.
The mixed factors caused by smoking were adjusted.
Contains estimates of the quantitative effects Associated between exposure and non-exposure
Groups exposed to biomass/solid fuel or data sufficient to calculate the effect estimate.
Sufficient sample size.
I have used a standard questionnaire or reported good questions to measure the respiratory symptoms of chronic bronchitis.
Lung function was measured according to the American chest Association standard.
Download the figureOpen figure 1 flow chart in the new tabDownload powerpoint showing studies related to chronic blocked lung disease (COPD)
Contact solid fuel.
Chronic bronchitis
LF, lung function;
Respiratory symptoms.
View this table: view the magnitude of the effects of chronic pulmonary obstruction associated with solid fuel smoke exposure view this table: both authors performed observations of chronic bronchitis associated with solid fuel smoke exposure at each stage. OK and JA)
Resolve differences through consensus.
According to the American Thoracic Society, the study of chronic lung obstruction (ATS)
7 and/or the global initiative for the Prevention of pulmonary obstruction (GOLD)
8 Standard, lung activity standard using 1 s Force breath (FEV1)
/Forced lung capacity (FVC)
Ratio |; t|; =0. 008)
Is an important contributor to heterogeneity (
Supplementary figures S12 and S13).
Heterogeneity tests performed on studies of chronic bronchitis in the same way did not show significant results.
Discussion of exposure to solid fuel smoke is considered to be an important risk of chronic lung and chronic bronchitis in LEDCs adults. This meta-
Analysis shows that exposure to solid fuel smoke is always associated with chronic lung and chronic bronchitis, regardless of the type of fuel exposure, the overall risk is more than doubled compared to non-fuel exposure
Biomass fuel users.
In more developed countries, smoking and occupational exposure are considered to be the main factors contributing to chronic lung arrest.
People with lower socio-economic status are at greater risk of chronic lung obstruction, 25-27, despite which factors (
Poor housing, poor nutrition, low income, no/poor education, for example)
Is the most important, to what extent is not clear.
Exposure to solid fuel smoke is also considered a major contributing factor, although this belief is based on alternative measurements of exposure, however, no studies have shown the relationship between direct measurement of biomass smoke exposure and chronic lung arrest prevalence. In this meta-
Analysis, estimates aggregated by Fuel Type, wood smoke (OR=4. 29, 95% CI 1. 35 to 13. 70)
Is the most important risk factor for chronic lung obstruction, followed by mixed biomass (OR=2. 49, 95% CI 1. 54 to 4. 01)and coal (OR=1. 84, 95% CI 1. 01 to 3. 35).
However, there are significant differences between the different studies included in this meta-study
Analysis was conducted in terms of design, handling of mixed factors, calculating risks for different reference groups, and exposure assessment.
All of these factors increase the significant statistical heterogeneity between different studies that may affect risk estimates.
Almost all studies of chronic lung disease have considered people over 35 years of age, which may increase the impact size as the prevalence of chronic lung disease increases, and is the highest among the elderly.
28 there are differences in exposure assessment, and most studies do not measure exposure directly, but use proxy measurements such as cooking time or whether room ventilation is present.
This lack of direct measurement can lead to overestimation or underestimation of the effect, always assuming the current measurement (
Usually measured ≤ 24 hours when obtained)
Really represents
More relevant term exposure in the development of chronic lung obstruction.
Summary estimates of chronic bronchitis from different types of fuels show results similar to those of the chronic lung obstruction, determining wood smoke (OR=2. 64, 95% CI 2. 12 to 3. 29)
As the most important risk factor, the second is mixed biomass smoke (OR=2. 46, 95% CI 1. 78 to 3. 39).
Respiratory questionnaires were used in studies related to chronic bronchitis (
Mainly the British MRC questionnaire)
: Studies that did not use the validation questionnaire were excluded from the meta-analysis.
The report and recall deviation cannot be ruled out by the questionnaire survey.
In developing countries, breathing, breathing difficulties and phlegm are considered to be normal to some extent, which may lead to breathing difficulties
Report symptom 29 if this is a differential expression between exposure and non-exposure
Exposed groups, which may affect the real risk.
Deviations may also occur in these studies due to the use of terminology.
In many languages, some words, such as "breathing", do not have an equivalent word.
In addition, in some parts of the world, people are reluctant to provide personal information, especially information about health, due to social taboos, especially in South Asia.
Finally, the review is restricted to include only English studies that may lead to published bias.
In LEDCs, it is common for a family to switch from one fuel to another.
Many people in urban areas, in the early years, may use cleaner fuel to cook.
This may lead to residual effects in the control group, so information about past fuel use should be collected in these studies.
In the study conducted before 2000, the chronic lung obstruction study using lung function criteria showed published deviations, showing higher results.
This may be related to the lack of clear research design issues in the described methods, such as the recruitment method, the level of training of technicians for lung capacity determination, differences in the use of trachea dilators on time at school in assessing chronic pulmonary obstruction or inconsistent use or lack of lung function equipment.
For chronic lung and chronic bronchitis, the allowance for exposure to mixed factors such as outdoor air pollution or toxic substances such as pesticides is insufficient (
Most rural residents are farmers or Housewives)
Or inadequate assessment of cigarette smoke exposure, whether active or passive, can lead to deviations in results.
Finally, heterogeneity may be true, and one explanation is the different toxicity of smoke from different biomass fuels.
No study provided information on the construction of a dose response function.
This should be seen as an important goal, as in the study of outdoor air pollution, simple linear relationships are unlikely to maintain exposure as documented in these studies.
Determining the shape of the dose-response curve will inform the need to reduce exposure levels to have a significant impact on health, taking into account the heterogeneity of fuel use shown in the analysis, which may vary depending on the fuel.
Future research needs to include all important risk factors, especially some form of measurement of direct exposure to biomass smoke.
What this measurement should be is not yet determined, but for now, the 24-hour average exposure (
Study on outdoor air pollution exposure)
It should be considered the most appropriate.
Mixed factors such as environmental tobacco smoke exposure, occupational exposure in dust environments, and smoking status should be considered.
The history of fuel use should be accurately recorded for longevity
The process of exposing simulation or estimation to biomass fuel smoke to determine any residual effects previously exposed to solid fuel smoke.
Health results should be measured using a validated instrument (
Is the lung function equipment used in the well
Trained technicians or questionnaires)
A clear definition of compliance with standard standards and agreed agreements.
Conclusion although there is heterogeneity in the estimation of design, measurement and quantitative effects included in the meta-study
Analysis, consistent evidence found that exposure to indoor air pollution was a risk factor for chronic lung and chronic bronchitis, and the risk was at least doubled, despite significant heterogeneity in the state and fuel types.
At present, there is not enough information to define the dose-response relationship and there is no epidemiology study to consider the potential differential toxicity of different fuel types, although this analysis shows the impact gradient of the fuel, but the impact of wood smoke is greatest.
Future studies should address these research design issues to improve risk estimates exposed to different fuel types.
The author thanks professor Tom Sorahan for providing statistical advice in preparing this manuscript.
OK is supported by doctoral students awarded by the University of Aberdeen.
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Funding from the University of Birmingham.
There is no competitive interest.
Uncommissioned source and peer review;
External peer review.