Background: Forced expiratory volume in 6 seconds (FEV(6)) is becoming a substitute of forced vital capacity (FVC). However, the Japanese predictive equation for FEV(6) has not been established, and the validity for the use of FEV(1)/FEV(6) for diagnosing airflow limitation in Japanese has not been confirmed.
Methods: Subjects aged 40 or older, who had participated in a community-based health check in Takahata, Japan, from 2004 through 2005, were enrolled. The smoking histories of these subjects were investigated using a self-reporting questionnaire. FVC, FEV(1), and FEV(6) were measured using spirometric machines. Predictive equations of FEV(6) were obtained from never-smoking subjects without history of pulmonary diseases by multiple linear regression assay.
Results: FEV(6) and FEV(1)/FEV(6) were significantly correlated with FVC (r=0.998, p<0.001) and FEV(1)/FVC (r=0.989, p<0.001), respectively. The cutoff values of percent predicted (%) FEV(6) and FEV(1)/FEV(6) for discrimination of having the restrictive lung disorder determined by %FVC <0.8 and having the airflow limitation determined by FEV(1)/FVC <0.7 were 0.80 and 0.72, respectively (%FEV(6): sensitivity=0.995, specificity=0.983, positive predictive value <PPV>=0.832, negative predictive value <NPV>=1.000; FEV(1)/FEV(6): sensitivity=0.942; specificity=0.971; PPV=0.787; NPV=0.993). When the 5th percentile the lower limit of normal values was used as criterion for discrimination of having airflow limitation, sensitivity, specificity, PPV, and NPV of FEV(1)/FEV(6) were 0.932, 0.985, 0.808, and 0.995, respectively.
Conclusion: The results of the present study suggest that %FEV(6) and FEV(1)/FEV(6) are excellent substitutes for %FVC and FEV(1)/FVC, respectively. We confirmed the validity of the use of FEV(6) and FEV(1)/FEV(6) for identifying pulmonary diseases in Japanese individuals.