Chronic Obstructive Pulmonary Disease: Epidemiology, Clinical Presentation, and Evaluation

The NHIS estimates for COPD have 2 important limitations. First, these estimates depend on the proper recognition and diagnosis of COPD by both the study participants and their health care providers. This would tend to bias the estimates toward counting fewer cases than actually exist. A bias in the opposite direction, however, is that the term chronic bronchitis in this survey is not precisely defined and could be interpreted as recurrent episodes of acute bronchitis. The finding that “chronic bronchitis” has been reported in 3% to 4% of children supports the presence of this potential bias. The second limitation is that this survey is not able to validate, through physiologic evaluation, whether airway obstruction is present or absent.

These limitations were addressed, in part, by separate nationally representative US surveys that include an examination component, such as the National Health and Nutrition Examination Surveys (NHANES) [17]. An analysis of these data from 1988–1994 and 2007–2012 [18] demonstrated that over 70% of people with evidence of obstruction (based on an FEV ₁/FVC < 70%) did not have a diagnosis of lung disease (COPD or asthma). In addition, people with evidence of obstruction had a higher risk of mortality whether or not they had diagnosed lung disease [18].

Evaluation of “reversibility” of the airway obstruction requires the administration of bronchodilator, which is not a part of most population-based studies. A subset of participants in the NHANES 2007–2012 survey received a bronchodilator, with a decrease in the estimated prevalence of obstruction from 20.9% to 14.0% [19]. However, a closer look at similar data from a study where all people got a bronchodilator reveal that only a small proportion of people with “reversibility” actually had a significant response to the bronchodilator [20]. In a clinic-based study of subjects with COPD who were aged 69 years and older, 31% demonstrated reversibility, defined as a 15% improvement (from baseline) in FVC and FEV ₁ following administration of an inhaled bronchodilator [21]. In this study, subjects with more severe obstruction were more likely to have reversibility but would also be more likely to continue to have diminished lung function after maximum improvement was obtained, thus being classified as having “partial reversibility.”

The presence of significant reversibility or partial reversibility in patients with COPD [15] and nonreversible airflow obstruction in asthma patients [22] demonstrates that these diseases can coexist or, alternatively, that there is overlap and imprecision in the ways that these diseases are clinically diagnosed.

Morbidity and Mortality

COPD is a leading cause of disease morbidity and mortality in the United States. The National Center for Health Statistics (NCHS) conducts ongoing surveillance of several health indicators nationally. The NCHS collects physician office visit data using the National Ambulatory Medical Care Survey [23], emergency department visit data and hospital outpatient data using the National Hospital Ambulatory Medical Care Survey [24], hospitalization data using the National Hospital Discharge Survey [25], and death data using the mortality component of the National Vital Statistics System [26]. The following data include the number and rate of COPD events in adults in the United States (using International Classification of Diseases, 9th Revision, Clinical Modification [ICD-9-CM], codes 490, 491, 492 and 496) in these data sets for the most recent years available.