Usefulness of FEV1/SVC to uncover airflow obstruction in subjects with preserved FEV1/FVC

Abstract

Background: Forced vital capacity (FVC) may substantially underestimate slow expiratory VC (SVC) in patients with airflow obstruction thereby leading to a “pseudo-normal” FEV 1 /FVC (i.e., ≥ 0.7 and/or ≥ lower limit of normality (LLN)). It remains unclear in which specific circumstances FEV 1 /SVC would be helpful to uncover airway obstruction despite preserved FEV 1 /FVC. Methods: 15,801 consecutive spirometric measurements showing pre-bronchodilator FEV 1 /SVC Results: Twenty percent (3,031/15,801) of subjects with FEV 1 /SVC 1 /FVC ≥ 0.7. Among those presenting with both ratios 1 /SVC 1 /FVC ≥ LLN. Most patients diagnosed with airflow obstruction only by FEV 1 /SVC had mild disease. However, they did present with lower FEF 25-75% , higher residual volume and higher specific airway resistance than those with preserved FEV 1 /FVC (p 1 /SVC increased markedly as a function of body mass index (BMI) (e.g., 11.9% in subjects with BMI 2 to 33.4% in those with BMI > 40 kg/m 2 ; p 30 kg/m 2 (2.04 (1.88-2.21)) and FEV 1 > 75% predicted (1.21 (1.10-1.32)) were associated with airflow obstruction diagnosed only by FEV 1 /SVC (p Conclusion: Compared to FVC, SVC increases the sensitivity of spirometry to detect mild airflow obstruction regardless the defining criterion ( 1 .