BACKGROUND
 
Asthma is a heterogeneous, chronic airway inflammatory disease in which pulmonary function tests (PFTs) might provide valuable information for diagnosis, assessment of clinical control, and estimation of future risk.
 
OVERVIEW
 
A 57-year-old never-smoking woman reported a 10-year history of recurrent dyspnea and occasional wheezing that worsened after COVID-19 two years earlier. Dyspnea progression was associated with weight gain (BMI = 33 kg/m2) in a background of type 2 diabetes and hypertension. She did report asthma in childhood, and her symptoms were typically precipitated by changes in the weather. Spirometry revealed mild and similar decreases in FEV1 and FVC, with normal FEV1/FVC ratio. Inhaled bronchodilator (BD) was associated with proportional increases in FEV1 (­ 0.37 L and 22%) and FVC (­ 0.39 L and 18%), with normalization of spirometry. DLCO was preserved. On the basis of her clinical history and functional data, she was diagnosed with asthma, with marked clinical improvement after a few weeks of treatment with medium-dose inhaled corticosteroids.
 
Reduced FVC and/or FEV1 with normal FEV1/FVC is a nonspecific finding that might signal restriction and/or obstruction. A commensurate improvement in FEV1 and FVC with the use of an inhaled BD indicates lung volume recruitment, revealing underlying airway disease. If these changes are large enough to normalize the results of spirometry, asthma is the most likely diagnosis. It should be noted, however, that “fixed” airflow obstruction with variable degrees of hyperinflation and gas trapping can be seen in patients with remodeled airways and severe asthma. Variable airflow obstruction over time is commonly seen in patients with asthma, usually improving either spontaneously or secondary to treatment. In equivocal cases, airway hyperresponsiveness can be revealed by bronchial challenge testing.(1) Once treatment is initiated, between-visit variability in FEV1 and BD responsiveness might provide ancillary information to gauge disease stability. Although it is not mandatory that maintenance or as-needed medications are withheld before testing, repeating PFTs under similar therapeutic conditions allows more meaningful interpretation. Low post-BD FEV1 (particularly < 60% predicted)(2,3) and higher BD responsiveness(3) are independent predictors of increased risk of exacerbation, even in patients with relatively modest symptom burden (Chart 1). Indirect airway hyperresponsiveness testing with the use of hypertonic saline to determine the dose of inhaled corticosteroids has been reported to decrease the number of asthma exacerbations in children when compared with treatment based only on symptoms.(4)
 

 
CLINICAL MESSAGE
 
PFTs are central to the diagnosis and follow-up of patients with asthma. For instance, undiagnosed obstruction in asthma patients is more common among those who have never undergone spirometry or who have never been referred to a pulmonologist.(5) However, PFT results should not be used in isolation. The best management approach involves a longitudinal assessment of clinical endpoints (symptom control and exacerbation frequency) and laboratory data (eosinophil count, total IgE, and specific IgE) under the modulating influence of key comorbidities (obesity, rhinosinusitis, nasal polyposis, and gastroesophageal reflux disease). There is renewed interest in using lung function parameters to improve asthma phenotyping, which may shed novel light into more complex biological mechanisms (endotypes) relevant to disease pathophysiology and, ultimately, treatment choices.(6)
 
AUTHOR CONTRIBUTIONS
 
All authors contributed to conceptualization, writing, reviewing, and editing.
 
CONFLICTS OF INTEREST
 
None declared.
 
REFERENCES
 
1.            Lougheed DM, Webb KA, O’Donnell DE. Breathlessness during induced lung hyperinflation in asthma: the role of the inspiratory threshold load. Am J Respir Crit Care Med. 1995;152(3):911-20. https://doi.org/10.1164/ajrccm.152.3.7663804
2.            Osborne ML, Pedula KL, O’Hollaren M, Ettinger KM, Stibolt T, Buist AS, et al. Assessing future need for acute care in adult asthmatics: the Profile of Asthma Risk Study: a prospective health maintenance organization-based study. Chest. 2007;132(4):1151-1161. https://doi.org/10.1378/chest.05-3084
3.            Denlinger LC, Phillips BR, Ramratnam S, Ross K, Bhakta NR, Cardet JC, et al. Inflammatory and Comorbid Features of Patients with Severe Asthma and Frequent Exacerbations [published correction appears in Am J Respir Crit Care Med. 2018 Apr 1;197(7):971]. Am J Respir Crit Care Med. 2017;195(3):302-313. https://doi.org/10.1164/rccm.201602-0419OC
4.            Ciółkowski J, Hydzik P, Rachel M, Mazurek-Durlak Z, Skalska-Izdebska R, Mazurek H. Childhood asthma treatment based on indirect hyperresponsiveness test: Randomized controlled trial [published online ahead of print, 2023 Jun 21]. Pediatr Pulmonol. 2023;10.1002/ppul.26556. https://doi.org/10.1002/ppul.26556
5.            Cherian M, Magner KMA, Whitmore GA, Vandemheen KL, FitzGerald JM, Bergeron C, et al. Patient and physician factors associated with symptomatic undiagnosed asthma or COPD. Eur Respir J. 2023;61(2):2201721. https://doi.org/10.1183/13993003.01721-2022
6.            Reyna ME, Bedard MA, Subbarao P. Lung Function as a Biomarker of Health: An Old Concept Rediscovered. Am J Respir Crit Care Med. 2023;208(2):117-119. https://doi.org/10.1164/rccm.202305-0911ED