FEV1/FEV6 for Detection of Airflow Obstruction: Response

Abstract

To the Editor: In his letter regarding our article,1Jing JY Huang TC Cui W et al.Should FEV1/FEV6 replace FEV1/FVC ratio to detect airway obstruction? A metaanalysis.Chest. 2009; 135: 991-998Abstract Full Text Full Text PDF PubMed Scopus (76) Google Scholar Dr. Pereira stated that substituting forced expiratory volume in 6 s (FEV6) for FVC to determine airflow obstruction would reduce the sensitivity of spirometry findings, especially in elderly patients with mild airflow obstruction.2Soares AL Rodrigues SC Pereira CA Airflow limitation in Brazilian Caucasians: FEV1/FEV6 vs. FEV1/FVC.J Bras Pneumol. 2008; 34: 468-472Crossref PubMed Scopus (12) Google Scholar This has also been noticed by other investigators.3Demir T Response: utilization of FEV6 in place of FVC may lead to the underestimation of mild airway obstruction [letter].Respir Med. 2005; 99: 1617Abstract Full Text Full Text PDF PubMed Scopus (6) Google Scholar, 4Crapo RO The role of FEV6 in the detection of airway obstruction [letter].Respir Med. 2005; 99: 1467Abstract Full Text Full Text PDF PubMed Scopus (3) Google Scholar One key point to Dr. Pereira's comments is the use of a cutoff value for FEV6 to determine airflow obstruction, which is also one cause of the heterogeneity of our study. For example, since FEV6 cannot be greater than FVC, one can anticipate that the false-positive values for the FEV1/FEV6 ratio should be zero. Why did it reach 30% in the study by Gleeson et al?5Gleeson S Mitchell B Pasquarella C et al.Comparison of FEV6 and FVC for detection of airway obstruction in a community hospital pulmonary function laboratory.Respir Med. 2006; 100: 1397-1401Abstract Full Text Full Text PDF PubMed Scopus (18) Google Scholar The reason for that is the lower limit of the reference values for FEV6 and FVC, both of which were obtained from the study by Hankinson et al.6Hankinson JL Odencrantz JR Fedan KB Spirometric reference values from a sample of the general US population.Am J Respir Crit Care Med. 1999; 159: 179-187Crossref PubMed Scopus (3337) Google Scholar Studies from Soares et al2Soares AL Rodrigues SC Pereira CA Airflow limitation in Brazilian Caucasians: FEV1/FEV6 vs. FEV1/FVC.J Bras Pneumol. 2008; 34: 468-472Crossref PubMed Scopus (12) Google Scholar and others3Demir T Response: utilization of FEV6 in place of FVC may lead to the underestimation of mild airway obstruction [letter].Respir Med. 2005; 99: 1617Abstract Full Text Full Text PDF PubMed Scopus (6) Google Scholar have shown a low sensitivity in patients with mild airflow obstruction, because they have also used a fixed ratio for the cutoff values of FVC or FEV6. Because the process of aging affects lung volumes, the use of this fixed ratio may result in the overdiagnosis of airflow obstruction in elderly persons, especially in those with mild disease. Therefore, the current Global Initiative for Chronic Obstructive Lung Disease guidelines7Global Initiative for Chronic Obstructive Lung Disease Global strategy for the diagnosis, management, and prevention of chronic obstructive pulmonary disease (updated 2008), 2008.Available at: http://www.goldcopd.orgGoogle Scholar advise that using a lower limit of normal values for FEV1/FVC ratio, which is based on a normal distribution and classifies the bottom 5% of the healthy population as abnormal, is one way to minimize the potential misclassification. If a lower limit is used for FEV6, it should be applied to FVC too. We think that no remarkable difference would be seen in the results while evaluating the FEV1/FEV6. Also, the simplicity of using FEV6 in place of FVC would be sacrificed if a lower limit for FEV6 is utilized. However, reference equations using post-bronchodilator therapy FEV1 and longitudinal studies to validate the use of the lower limit of normal are urgently needed. The only such equations currently available are those from the National Health and Nutrition Examination Study III study. The primary significance of using the FEV1/FEV6 ratio is to reduce the misclassification rates in the multitude of settings where a volume-time plateau is rarely obtained. Many people operating spirometers have misinterpreted the traditional spirometry guidelines, which allow them to quit coaching patients after 6 s (even when the patient could have exhaled much more air), and this practice frequently causes the reported FEV1/FVC ratio to be higher than the true value. The use of the reference values for FEV1/FEV6 ratio is more appropriate in these settings, since it reduces the misclassification for detecting airway obstruction when compared with using the FEV1/FVC ratio reference values. FEV1/FEV6 for Detection of Airflow Obstruction: Better Forget ItCHESTVol. 136Issue 6PreviewTo the Editor: Full-Text PDF