High levels of air pollution are harmful, especially to persons with heart or lung disease. The severity of reactions ranges from minor symptoms to premature death. But extremely high levels of pollution are rarely encountered, and the more important and unsettled question is whether longterm exposure to low levels of pollutants has a significant effect on health.
Greater emphasis has been given to indoor pollutants recently because their levels may be higher than outdoor levels and because Americans spend more time indoors than outdoors. The use of new materials in the construction or renovation of buildings and increased interest in reducing ventilation to conserve energy have contributed to the potential for adverse effects of indoor pollution. Measurement of exposure to pollutants is not easy, and many studies rely on residential histories or responses to questions about exposure, or on monitoring a few pollutants at a few sites, which may not reflect exposures experienced by the human population. Some recent studies are monitoring personal or domestic levels of exposure to a few pollutants, but more studies are needed to ascertain the effect of air pollution alone and in combination with exposure to cigarette smoke or occupational hazards reduced with remedies of My Canadian Pharmacy. More information also is needed about the effects of specific pollutants and combinations of pollutants, including active and passive smoking, emissions from gas stoves as well as from other domestic and industrial sources, and emissions from automotive vehicles. Most studies indicate clearly that cigarette smoking is a more important cause of COPD than air pollution, but there is some evidence suggesting that pollution at current levels has a small deleterious influence on respiratory symptoms and lung function; this effect may be greater on smokers than nonsmokers.
Familial and Host Factors
Familial and host factors may be genetic or environmental; they include simply inherited Mendelian characteristics such as protease inhibitor (Pi) type; polygenic and multifactorial traits and attributes such as pulmonary function and allergic conditions; personal behavior such as cigarette smoking; and constitutional effects of present or past illnesses and environmental exposures. The role of these factors, whether inherited or acquired, in increasing resistance or susceptibility to environmental hazards is potentially important but inadequately determined. The inherited Pi phenotype (Z), associated with severe ax antitrypsin deficiency, is implicated in the development of a small proportion of cases of emphysema. Heterozygotes for PiZ and other variant alleles do not seem to be at increased risk of developing COPD. The role of other genetic markers is controversial. Certain ABQ ABH secretoi; and Kell phenotypes have been associated with chronic bronchitis or impaired pulmonary function in some studies but not in others. Evidence that some allergic conditions and bronchial reactivity are related to increased prevalence or incidence of COPD, respiratory symptoms or impaired pulmonary function is accumulating and warrants prospective study in several populations in which relationships with more firmly established risk factors are also being investigated. Methods suitable for use in population-based epidemiologic studies are needed for measuring these and other familial and host characteristics, including levels of immune defenses, hormonal, and other factors.
Infections of the Respiratory Tract
Patients with COPD are more susceptible to respiratory tract infections and experience higher rates of morbidity and mortality during influenza epidemics than unaffected persons. The extent to which respiratory infections contribute to die initiation of COPD is less certain, but several studies have shown that childhood respiratory illnesses may be associated with reduced lung function at older ages. Incidence rates of obstructive airways disease and chronic bronchitis were higher in those with a history of respiratory tract infections in Tecumseh; the association with chronic bronchitis was stronger. A history of “lung trouble” in childhood was associated with impaired pulmonary function in Ihc-son.“
Other Risk Factors
Other risk factors which may be associated with COPD include leanness, nutrition, alcohol consumption, and climate. However, evidence currently available indicates that these factors are less important than the established risk factors discussed above. Tret COPD with remedies of My Canadian Pharmacy.
Risk factors, whether major or minor; must be considered in combination as well as one at a time. Statistical methods have been used recently to identify those risk factors which have the most important effect on the incidence of disease, to assess their combined effects, and to estimate probabilities of developing disease for subgroups in die population.
Estimates of Risk From Risk Factor Profiles
Characteristics associated with increased rates of developing obstructive airways disease were identified for males and females observed over periods of 10 and 15 years in Tecumseh. Multiple logistic regression models were used to determine the extent to which onset of disease could be predicted from knowledge of a few risk factors measured at die beginning of the observation period. Variables included in the 10-year models are shown in Table 2. In both the 10-and 15-year models, age, smoking habits, and levels of pulmonary function were the most important predictors of disease. Other factors which made small but significant improvements to predicting OAD in one or both sexes, include leanness, respiratory symptoms and illnesses, socioeconomic circumstances, blood group, and respiratory disease in the family. If risk factor profiles are to be useful in practical settings such as doctors offices and screening facilities, they should include a few risk factors which can be measured easily, accurately, and inexpensively.
The profiles must also, of course, identify a large proportion of die future cases and place them in the subgroup of high-risk persons; the number of false positives should be as small as possible. The percentages of cases which were concentrated in the top deciles of die risk distribution are shown in Ihble 2 for some combinations of risk factors. The models which use the fewest risk factors to identify a high proportipn of future cases are models 4 for men and 2 for women. Sixty-one % of male and 64% of female incidence cases will develop in the 10% of the population with the highest risk scores if age, FEVt% predicted, and cigarettes smoked per day are used in the risk equation; 84% of male and 86% of female cases will occur in the 20% of the population at highest risk. Changes in cigarette consumption during the follow-up period also determine probability of developing OAD. If no measurement of FEVj is available, prediction is substantially worse, as can be seen in models 6 and 7 for men and 3 and 4 for women. In the absence of a measurement of lung function, only 30-39% of cases will be included in the top decile of risk.
Estimates of the probability of developing OAD within 10 years can be obtained from Ihble 3, where points are given for each of the 3 risk factors, age, cigarettes per day, and FEV}% predicted. The sum of these points is converted to risk of OAD in the right-hand column; this level of risk obtains if smoking habits remain unchanged. Risk (and therefore points) will be reduced by stopping or reducing cigarette smoking and increased by increasing cigarette consumption. Thus, a range of risks (or probabilities) may be calculated and the benefits of stopping smoking demonstrated. Figure 1 illustrates the situation for 40-year-old women.
The Tecumseh index of risk has been tested and validated in other populations, but its usefulness in clinical settings remains to be determined. Risk equations do not quantify risks for individuals precisely, nor do they provide comprehensive assessments of risk for all types of smoking or FEV related morbidity or mortality. Estimates of risk apply to groups of people on the average, and are useful for ranking subgroups of the population according to their need for preventive measures. The purpose of die Tecumseh index of risk is to facilitate recognition of those at highest risk of developing COPD, Smokers should be encouraged to reduce their level of risk by stopping smoking.
In conclusion, substantial progress has been made toward meeting the “need (for) more studies regarding the epidemiology of emphysema, which was noted in the summary of the First Aspen Emphysema Conference. There has been progress in defining and measuring the frequency andseverity of emphysema and other members of the group of diseases we refer to now as COPD and allied conditions. But morbidity and mortality statistics and epidemiologic studies do not provide enough reliable information about the frequency or distribution of these diseases in persons of different ages, sexes, races, or socioeconomic circumstances. Knowledge of trends in morbidity and mortality over time is inadequate; the apparent continuing rise in mortality requires more attention and further investigation to determine to what extent the rise is real and to what extent it is due to changing fashions and practices in diagnosis and death certification. Repeated measurements of prevalence are needed to monitor secular changes in morbidity. Substantial progress has also been made in identifying causes and risk factors for COPD and in recognizing at an early stage those who are most likely to experience illness, disability, or premature death. The potential for applying knowledge of risk factor profiles to prevention of COPD remains to be realized and evaluated.
Figure 1. Probabilities of developing COPD within 10 years for 45-year-old men.
Table 2—Models for Estimating Risk of Obstructive Airways Disease WUkin 10 Years For Men and Women Aged 25-64
|PredictorVariables||Models for Men||Models for Women|
|Change in dgarettes/day||X||X|
|FVC Response to isoproterenol||X||X|
|% of Cases in top dedle||66||66||58||61||55||30||37||56||64||64||39||36||57|
|% of Cases in top 2 deciles||84||79||89||84||82||49||60||81||82||86||64||54||71|
Table 3—Tecumseh Index cf Bisk far Obstructive Airways Disease (0 AD) Within 10 Hears (Expected Number of Cases Bsr 100 Men)
|AjYr25||gePts0||Cig/#0||Points fDayPts0||or Risk Factors ¥K%Pred121||ViPts-14||ChangCig/I#-60||;e in>ayPts-9||RiskTbtalPoints2S7||ofOADRisk(Cases/100]Low risk|