• Nikhil A Huprikar, Andrew J Skabelund, Valerie G Bedsole, Tyson J Sjulin, Asmita V Karandikar, James K Aden, and Michael J Morris.
• Pulmonary/Critical Care Service, Brooke Army Medical Center, Joint Base San Antonio (JBSA) Fort Sam Houston, Texas. nikhil.a.huprikar.mil@mail.mil.
• Respir Care. 2019 Jul 1; 64 (7): 786-792.

BackgroundObstructive lung disease is diagnosed by a decreased ratio of FEV1 to the vital capacity (VC). Although the most commonly used VC is FVC, American Thoracic Society guidelines suggest alternative VCs, for example, slow VC (SVC), may offer a more-accurate evaluation of breathing capacity. There is recent evidence that using only FEV1/FVC underrecognizes obstruction in subjects at high risk and who are symptomatic. Previous studies have indicated that healthy individuals show a minimum difference between FVC and SVC; however, testing of individuals with asthma and who are symptomatic indicates that SVC can be markedly larger than FVC.ObjectiveTo evaluate the differences among SVC, FVC, and SVC-based measurements in the diagnosis of symptomatic obstructive lung disease.MethodsA retrospective analysis was performed of spirometry and plethysmography measurements from studies conducted between 2011 to 2015. We established a pulmonary function database that incorporated predictive equations from the National Health and Nutrition Examination Survey III (NHANES III). The SVC to FVC difference was calculated. FEV1/SVC was compared with FEV1/FVC by using NHANES III lower limit of normal values.ResultsA total of 2,710 studies with 2,244 subjects were reviewed. Spirometric obstruction, as defined by NHANES III, was identified in 26.1% of the studies (707/2,710). The mean (± SD) difference between SVC and FVC was 375.0 ± 623.0 mL and 258.8 ± 532.5 mL in those with and those without obstruction, respectively. Subgroup and multivariate analysis demonstrated age, body mass index, and FEV1 associated contributions to the difference between SVC and FVC. By using FEV1/SVC, the prevalence of obstruction increased from 26.1 to 45.0% (1,219/2,710) and identified 566 additional studies of subjects with obstruction. Fifty-four percent of the subjects with newly-identified obstructive lung disease (305/566) had smoking histories, and 67.4% (345/512) received medications for obstructive lung disease.ConclusionsThe isolated use of FVC-based diagnostic algorithms did not recognize individuals with symptomatic obstructive lung disease. Recognizing the difference between SVC and FVC measurements in subjects will improve testing and diagnosis of obstructive lung disease.Copyright © 2019 by Daedalus Enterprises.

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