Pulmonary Function Tests
Spirometry
Spirometry measures the maximal expiratory flow and exhaled volume during a forced expiratory vital capacity maneuver. The test is widely available, reproducible, and highly standardized in terms of performance, methodology, and equipment specifications.
Spirometry is a useful measure of severity of airflow limitation in asthma and is predictive of clinical outcomes. Normal standardized values for spirometry are well established for healthy, multiethnic populations. It is a safe and low-risk procedure that can be performed repeatedly for long-term monitoring.
The prebronchodilator response and postbronchodilator response maneuver involves a baseline spirometric value compared to a postbrochodilator spirometric value (ie, a repeat spirometry 15 min after two to four inhalations of albuterol). An improvement of 12% or more in the measurement of forced expiratory volume in 1 second (FEV1) improvement of 12% or greater from baseline represents the presence of reversible airflow obstruction, which usually means that the patient has asthma. [16, 17] See the image below.
Asthma in older adults. Spirometric data plot. Pre-bronchodilator forced expiratory volume-one second (FEV1) = 1.77 L, post-bronchodilator FEV1 = 3.11 L, approximating a 75% change or airway reversibility.
Peak expiratory flow
Peak expiratory flow (PEF) is a measure of maximum instantaneous expiratory flow and is used as an indicator of airway caliber in asthma. The advantage of peak expiratory flow is that the test can be self-administered on a daily basis, and the results can be recorded manually or electronically to attain the day-to-day or intraday variability. [17]
Peak flows may be used to monitor changes in airflow in response to treatment, in relation to exercise or other provocations, or to determine if shortness of breath (or other chest symptoms) is associated with a change in airflow measurement when trying to differentiate the various causes for shortness of breath (ie, cardiac vs pulmonary).
Methacholine challenge
Methacholine inhalation challenge (or, bronchoprovocation test) provides a measure of airway responsiveness and has been used as one indication of whether a patient has asthma. A negative methacholine finding is a strong indicator that the patient does not have asthma, whereas a positive finding does not mean that the patient does have asthma.
Methacholine challenges have proven useful in the evaluation of coughing patients and in the evaluation of vocal cord dysfunction. The challenge is performed by inhalation of increasing concentrations of methacholine, which is a cholinergic agonist, until the forced expiratory volume in 1 second (FEV1) falls by 20% or more. [17]
Mannitol challenge
The mannitol inhalation challenge is a promising method of assessing airway hyperresponsiveness by imposing an osmotic stress on the airways. It may induce bronchoconstriction by the same mechanism as exercise or isocapnic hyperventilation. [17]
Mannitol is used for the same indications as methacholine but is easier to perform and less dangerous for individuals who may have airway overreactivity.
Exercise challenge
An exercise challenge measures airflow limitation after a maximum exercise test. A decline in forced expiratory volume in 1 second (FEV1) of 10% or more is a positive result and highly specific for a diagnosis of asthma in children but less so in adults. [17]
Isocapnic hyperventilation challenge
The isocapnic hyperventilation challenge is conducted via the inhalation of cold, dry air, which induces bronchoconstriction in many people with asthma. However, it is not considered a diagnostic test. Wide application of the test is limited by the lack of standardization. [17]
Imaging Studies
Chest radiography
A chest radiograph may reveal hyperinflation of the lungs for a diagnosis of asthma. This imaging modality may be an important part of the work-up for differential diagnosis of other respiratory diseases.
Sinus computed tomography (CT) scanning
A sinus CT scan may reveal evidence of rhinosinusitis or nasal polyposis, which might help with the diagnosis (eg, Samter triad of asthma, aspirin sensitivity, nasal polyposis).
Other Tests
Allergy skin testing
Adults with asthma often have an allergic trigger; therefore, skin tests are useful to identify the offending triggers. Strategies for allergen avoidance can then be developed, (eg, cat allergy, dust mite allergy).
pH probe evaluation
A a=pH probe evaluation is a procedure that involves placing a pH probe attached to a monitor and then measuring in real-time the amount of stomach acid that is refluxed within the esophagus. This may establish a diagnosis of gastroesophageal reflux disease (GERD) or laryngopharyngeal reflux (LPR) disorder as the etiology of chronic cough. GERD is also known to trigger and exacerbate asthma. LPR can cause postnasal drip, throat clearing, cough, and hoarseness.
Lifestyle modifications include weight loss, low-fat diet, decreased caffeine and alcohol intake, raising the head of the bed about 6 inches, and avoiding meals 2-3 hours prior to reclining. Medications that reduce gastric acid secretion may also be helpful. Oral steroids may exacerbate GERD symptoms. [18]
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Asthma in older adults. Lung tissue normal versus constricted.
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Asthma in older adults. Airway histology and pathology.
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Asthma in older adults. Allergic and nonallergic triggers.
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Asthma in older adults. Spirometric data plot. Pre-bronchodilator forced expiratory volume-one second (FEV1) = 1.77 L, post-bronchodilator FEV1 = 3.11 L, approximating a 75% change or airway reversibility.
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There has been an upward trend in the prevalence of asthma across all age groups since 2001. Courtesy of the CDC (https://www.cdc.gov/asthma/data-visualizations/prevalence.htm).
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Asthma prevalence by age, 2017. Courtesy of the CDC (https://www.cdc.gov/asthma/data-visualizations/prevalence.htm).
