Chronic bronchitis is defined by symptoms of a productive cough 3 months out of the year for at least 2 consecutive years. Causes include chronic or repeated exposures to silica, coal, grain, cotton, wood, or asbestos dusts; also to welding fumes, firefighting, and dusts in livestock confinement buildings. The length of exposure necessary to cause chronic bronchitis is probably years or decades, not days or months. [Rosenstock, p. 322-5] Chronic bronchitis has been described in boiler cleaners exposed to vanadium pentoxide. [ACGIH] "Pulmonary Disease, Chronic Obstructive" is defined as, "A disease of chronic diffuse irreversible airflow obstruction." Subcategories of COPD include chronic bronchitis and emphysema. [National Library of Medicine MeSH Database] "It is unusual for a person to have clinically apparent COPD without a history of smoking for at least 20 pack years, and most patients have at least 40 pack years of exposure. [Cecil, 23rd Ed, p. 619] "Occupational exposures are also associated with increased risk for accelerated loss of lung function, although the effect is usually small compared to the effect of cigarette smoking." [Murray, p. 1126] "Most of the studies summarized throughout this chapter have reported statistically significant reductions in airflow rates among groups of exposed workers compared to nonexposed workers. Symptoms of cough, phlegm, and wheezing are variable reported to be increased or not increased. The relevance of these findings with respect to disability and clinical outcome is strongly debated." [Harber, p. 447] "Evidence of chronic airflow obstruction in relation to measures of welding exposure has been seen in most but not all studies designed to investigate this outcome. . . . Functional changes appeared to be reversible only among those welders who were consistently using local exhaust ventilation." [Asthma in the Workplace, p. 380-1]"The biological plausibility of the capacity of occupational exposures to irritating dusts, gases, and fumes to cause chronic obstructive pulmonary disease (COPD) is high. Epidemiological evidence from both worker cohort and community studies supports an increased risk of COPD associated with such exposures. The occupational contribution to the burden of COPD is sufficiently great that preventive interventions are warranted." [Balmes JR. Occupational contribution to the burden of chronic obstructive pulmonary disease. J Occup Environ Med. 2005 Feb;47(2):154-60] FEV1/FVC Ratio of 70% Misclassifies Patients with Obstruction at the Extremes of Age." [
PMID 16840402] "Applying the current GOLD criteria (FEV1/FVC < 0.70) to post bronchodilator spirometry, the prevalence of COPD of adults aged 40 years and over was 24.2%. In contrast to this, utilization of the lower limit of normal as a threshold for the FEV1/FVC ratio (FEV1/FVC < LLN) demonstrated a prevalence of 15.3%. Prevalence of doctor-diagnosed COPD (reported physicians diagnosis of COPD, emphysema, or chronic bronchitis) was 5.6%" [
PMID 21637369] Emphysema causes increased air volumes, asbestosis causes a restrictive pattern, and both cause decreased diffusing capacity. [
PMID 15751618] and [
PMID 16570255] In 1965 in the United States, 42.4% of adults aged 18 years and older were smokers compared with 19.3% in 2010. "Depending on the spirometric criteria used, estimates of prevalence of COPD based on spirometry tests may be as much as double the estimates derived from self-reported information." [
PMID 23619732] See "Occupational COPD and job exposure matrices: a systematic review and meta-analysis." [
PMID 28260879]