Forced Expiratory Volume in 6 s (FEV6) and FEV1/FEV6 Values as a Viable Alternative for Forced Vital Capacity (FVC) and FEV1/FVC Values During Pregnancy in South East Nigeria: A Preliminary Study

Abstract

Background: Forced expiratory volume in 6 s (FEV₆) and FEV₁/FEV₆ ratio have traditionally been used as a surrogate for forced vital capacity (FVC) and FEV₁/FVC in the assessment of spirometric lung function in nonpregnant subjects. However, the existence of this relationship during pregnancy is yet to be ascertained. Aim: The aim of this study was to determine if FEV₆ and FEV₁/FEV₆ can effectively be used instead of FVC and FEV₁/FVC in the interpretation of lung function test during pregnancy. Subjects and Methods: This study was a descriptive cross‑sectional study carried out among 200 pregnant women who were recruited by using systematic random sampling during the period between April and October 2011. One hundred matched nonpregnant women served as control. A standard spirometer was used to determine the FVC, FEV₆, FEV₁/FVC, and FEV₁/FEV₆. Data analysis was done using SPSS version 11.0 (Chicago, IL, USA). Values were recorded as mean (standard deviation), and also median and interquartile ranges. The one‑way analysis of variance, Mann–Whitey U and the Kruskal–Wallis were used to test for significance where applicable. P <0.05 were considered to be significant. Results: All the values were within normal range, but the FVC and FEV₆ decreased significantly while the FEV₁/FVC and FEV₁/FEV₆ increased as pregnancy progressed. However, for first and last trimester, FVC differed significantly from FEV₆. The values of the FVC were comparable to the values of FEV₆. The FEV₁/FVC and FEV₁/FEV₆ ratio were similar and well above the 0.7 cutoff for obstructive lung diseases. Conclusion: FEV₆ requires a short exhalation time and can effectively be used in place of FVC in evaluation of lung function test during pregnancy. The FEV₁/FEV₆ may be applied as a proxy for FEV₁/FVC in pregnant and nonpregnant women. 

Keywords: FEV₆, FEV₁/FEV₆, FEV₁/FVC, Forced vital capacity, Pregnancy, South East Nigeria