Obstructive Lung Diseases
In patients with obstructive lung disease, changes in the bronchi, bronchioles, and lung parenchyma can cause airway obstruction. Obstructive lung diseases can be categorized as reversible or irreversible, although many cases may have some degree of both reversible and irreversible obstruction.
Reversible obstructive diseases are grouped under the term asthma. In patients with asthma, the airways are hyperresponsive and develop an inflammatory response with bronchospasm to various stimuli; the specific cause and duration of the bronchospasm can vary. In some persons, allergic immunoglobulin E (IgE)– mediated reactions to defined antigens cause bronchospasm. In many individuals with asthma, however, the cause of abnormal airway reactivity remains unknown. Precipitating factors may include exercise, aspirin, sulfites, tartrazine dye, emotional stress, cold air, environmental pollutants, or viral infection. Bronchial smooth muscle constriction, mucosal edema, excess mucus accumulation, and epithelial cell shedding all contribute to airway obstruction. This obstruction may be reversible, either spontaneously or with treatment. One marker of eosinophilic airway inflammation is an increase in exhaled nitric oxide; identifying this increase may be important in measuring an individual’s responsiveness to therapeutic intervention. Mepolizumab, a monoclonal antibody, is approved for use in cases of severe eosinophilic asthma.
Irreversible obstructive disease (sometimes known as chronic obstructive pulmonary disease [COPD]) comprises a group of conditions in which forced expiratory flow is reduced in either a constant or a slowly progressive manner over months or years. COPD is the third leading cause of death in the United States. The Global Initiative for Chronic Obstructive Lung Disease (GOLD), an international consortium working to improve prevention and treatment of COPD, publishes a guide on the diagnosis, classification, and management of this condition. The guide, which is updated regularly, can be downloaded from the GOLD website (www.goldcopd.org). GOLD offers a framework for the management of COPD. Some conditions, such as cystic fibrosis or bronchiectasis, which are either secondary to recurrent necrotizing bacterial infections or which occur as part of Kartagener syndrome, have an identifiable cause. However, most irreversible obstructive diseases, such as emphysema, chronic bronchitis, and peripheral airway disease, cannot be ascribed to specific conditions; rather, they represent an individual response to cigarette smoking and various airborne pollutants. For example, such responses occur in patients with either α1-antitrypsin deficiency (associated with certain forms of emphysema) or airway hyperactivity and mucus hypersecretion (as in bronchitis). The pathologic consequences of the abnormal response result in specific damage to lung tissue. Emphysema is characterized by pathologic enlargement of the terminal bronchiole air spaces and by destruction of the alveolar connective tissue septa. Bronchitis is characterized by hypertrophied mucous glands in the bronchi; in peripheral airway disease, only the small airways demonstrate fibrosis, inflammation, and tortuosity.
Obstructive sleep apnea (OSA) has similar pathophysiologic processes to COPD: compromised gas exchange that leads to hypoxia and hypercapnia. OSA is a breathing disorder characterized by the narrowing of the upper airway, which impairs normal ventilation during sleep. This physical disruption of the upper airway distinguishes OSA from central sleep apnea, which occurs as a result of the brain temporarily not transmitting signals to the muscles that control breathing, leading to insufficient ventilation and compromised gas exchange. The current prevalence of OSA in the United States is estimated at 14% for men and 5% for women. The prevalence of OSA is much higher in patients with coronary artery disease, congestive heart failure, arrhythmias, refractory hypertension, type 2 diabetes mellitus, and polycystic ovary disease. The fragmented sleep experienced by individuals with untreated OSA can lead to many negative consequences, including daytime sleepiness, cognitive disfunction, and decreased quality of life. Untreated OSA is also associated with an increased risk of developing cardiovascular disease, resistant hypertension, coronary artery disease, congestive heart failure, arrhythmias, stroke, and metabolic dysregulation that affects glucose control. In order for OSA to be diagnosed and evaluated, a patient must undergo polysomnography, a type of sleep study that records the many biophysical changes that occur during sleep, including respiratory functions. Treatment of OSA has been shown to improve the individual’s quality of life, decrease motor vehicle collisions, and reduce the chronic health consequences associated with untreated OSA.
Global Initiative for Chronic Obstructive Lung Disease. Global strategy for the diagnosis, management, and prevention of chronic obstructive pulmonary disease (updated 2017). www.goldcopd.org/gold-reports-2017. Accessed February 21, 2019.
Song WJ, Kim HJ, Shim JS, et al. Diagnostic accuracy of fractional exhaled nitric oxide measurement in predicting cough-variant asthma and eosinophilic bronchitis in adults with chronic cough: a systematic review and meta-analysis. J Allergy Clin Immunol. 2017;140(3):701–709.
Excerpted from BCSC 2020-2021 series: Section 1 - Update on General Medicine. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.