Chapter 14 - Techniques to evaluate asthma

Abstract

The evaluation of the asthma patient combines history, lung physiology tests, and mechanistic tests of airway inflammation to inform diagnosis and management. Subjective measures assess asthma control in two principal domains: impairment and risk of adverse events. The impairment domain includes daytime asthma symptoms, frequency of rescue bronchodilator use, limitations in activity, and nighttime awakenings. The risk domain assesses frequency of exacerbations requiring urgent medical attention or systemic corticosteroids. However, patients may misreport the asthma history due to diagnoses that mimic asthma, lack of historical recall, or misperception of dyspnea. Therefore, physiologic testing such as spirometry or provocation testing is important to confirm reversible airway obstruction and objectively monitor asthma severity. Spirometry is the primary method to measure airway obstruction by measuring a patient’s maximal expiratory flow rate and demonstrates airway reversibility by measuring bronchodilator response. However, accurate spirometry requires good patient technique, accurate reference values, and can be affected by medications. When initial spirometry is nondiagnostic, provocation testing can assess airway hyperresponsiveness consistent with asthma with triggers that act directly on airway smooth muscle or indirectly by stimulating inflammatory cells to release mediators. Mechanistic evaluations investigate the underlying immunologic pathogenesis of the patient’s asthma to help design therapies specific to their disease mechanism. Allergy testing helps identify environmental triggers to avoid and the potential use of anti-IgE biologics or allergen immunotherapy. Peripheral blood eosinophils are used to predict response to biologics that target the T2-high inflammatory pathway. An elevated fractional exhaled nitric oxide measurement suggests either nonadherence or an inadequate inhaled corticosteroid dose. Taken together, the clinician combines subjective, physiologic, and mechanistic techniques for evaluating asthma to inform diagnosis and management. This chapter will review the subjective, physiologic, and mechanistic evaluations available for the optimal assessment of the asthma patient.