Suggested Reading
Marik PE. Aspiration pneumonitis and aspiration pneumonia.
N Engl J Med.
2001;344(9):665–671.
ASTHMA
Definition
Asthma is a highly prevalent and chronic inflammatory disorder in which the airway smooth muscle undergoes exaggerated contractions and is abnormally responsive to external stimuli. The best defined and most commonly identified cause of this inflammation is inhalation of allergens.
Classification of bronchial asthma can be based on age, etiology-associated characteristics, or severity. The pattern of disease presenting at different ages is distinct. In the first 2 years of life, wheezing and bronchiolitis are not distinguishable, and the most common cause of these episodes is infection with the RSV. In older children and young adults, by far the most commonly identified cause of asthma is sensitization to one of the most common inhalant allergens, particularly those encountered indoors.
Asthma that presents after 20 years of age provides a complex problem, and there is a wider differential diagnosis. Major causes include simple allergic asthma in adults, intrinsic asthma associated with chronic hyperplastic sinusitis, allergic bronchopulmonary aspergillosis, and wheezing associated with chronic obstructive lung disease.
Among adults aged >40 years who develop severe asthma for the first time, almost 50% may have intrinsic asthma (negative skin tests to common allergens, no family history, persistent eosinophilia). Late-onset asthma, which is frequently not associated with atopy, may be linked to workplace (occupational exposure to sensitizing chemicals).
Who Should Be Suspected?
Classic symptoms of asthma are intermittent dyspnea, cough, and wheezing. These symptoms are nonspecific and sometimes difficult to distinguish from other respiratory diseases. Patients may present to clinics or the emergency department with acute symptoms of breathlessness, wheezing, and coughing. Alternatively, they may present between episodes with normal or nearnormal lungs. Asthma may develop at any age, although new-onset asthma is less frequent in elderly compared to other age groups. Seventy-five percent of the cases are diagnosed before the age 7.
Asthmatic symptoms characteristically come and go, with a time course of hours to days, resolving spontaneously with removal of triggering stimulus or in response to antiasthmatic medications. Characteristic triggers of asthma include cold air, exercise, and exposure to allergens. Allergens that typically trigger asthmatic symptoms include dust, molds, furred animals, cockroaches, and pollens. Viral infections are also common triggers.
Diagnostic Findings
The diagnostic tools should include history, physical examination, pulmonary function tests (PFTs), and other laboratory evaluations.
PFTs: Measurement of peak expiratory flow rate (PEFR) and spirometry are the two PFTs most often used in the diagnosis of asthma. Spirometry is used to measure the amount of air a person can breathe out and the amount of time taken to do so. Forced vital capacity (FVC): maximum volume of air that can be exhaled during a forced maneuver. Forced expired volume in 1 second (FEV
1
): volume expired in the first second of maximal expiration after a maximal inspiration. This is a measure of how quickly the lungs can be emptied. FEV
1
/FVC: FEV
1
expressed as a percentage of the FVC gives a clinically useful index of airflow limitation. The ratio FEV
1
/FVC is between 70% and 80% in normal adults; it is influenced by the age, sex, height, and ethnicity and is best considered as a percentage of the predicted normal value. Variability of >20% in PEFR, a reversible reduction in FEV
1
and FEV
1
/FVC, and heightened sensitivity to bronchoprovocation are findings consistent with asthma.
