Development of reference values and equations for the pulmonary function of Nigerian children aged 6–11 years measured with digital peak flow meter and its validation against local and the Global Lung Function Initiative (GLI) equations

Abstract

Background: Spirometry reference equations (REs) assist diagnosis, monitoring and prognostication of chronic respiratory diseases (CRDs) like asthma. However, scarcity of spirometers in low-resource settings hampers optimal care of CRDs. Alternatively, cheap, widely-available mechanical peak flow meters, which measure peak expiratory flow (PEF), may serve limited usefulness in such settings. Better still, digital or electronic peak flow meters (ePFM) are more useful than mPFM because they measure forced expiratory volume in one second (FEV1), in addition to PEF. However, their use requires REs fitted specifically to ePFM-measured PEF and FEV1 of local populations. We thus determined the mean PEF and FEV1 of Nigerian school-age children, measured with an ePFM, and their determinants (including measures of body size and proportionality); and compared the PEF and FEV1 values with previously-published Nigerian, non-Nigerian equations and the Global Lung Function Initiative (GLI)’s race-specific and race-neutral equations. Methods: We analysed cross-sectional measurements of body-size, body-proportionality and lung function (LF) data of healthy 6–11-year-old Nigerian children living in Lagos, south-west Nigeria. An ePFM (Asma-1™, Vitalograph, UK) was used to measure each child’s PEF and FEV1. Bland-Altman analysis was used to validate measured PEF against published PEF equations [acceptable limits-of-agreement (LoA) defined as <20% of sex-specific mean PEF], while GLI’s validation criteria were used to validate measured FEV1 against GLI FEV1 equations {mean [standard deviation (SD)] predicted FEV1 Z-scores <0.5 (1.0)}. Results: A total of 766 participants with mean age 8.9 years (SD =1.6), comprising 46.9% boys, achieved mean PEF of 235.8 L/min (SD =52.0) and FEV1 of 1.40 L (SD =0.34); being lower in girls (P<0.001). Height (r=0.73–0.86), lower limb length (r=0.67–081), weight (r=0.62–0.76), age (r=0.60–0.66), upper-segment volume (r=0.58–0.69), upper-segment length (r=0.54–0.61) and chest circumference (r=0.52–0.66) were strongly correlated with both PEF and FEV1. Agreement was poor between measured PEF and PEF predicted by Nigerian and non-Nigerian equations (LoA >20% sex-specific mean PEF). Of the GLI FEV1 equations, only the GLI-African-American equations fitted the FEV1 of both sexes [mean (SD; % lower limit of normal, % upper limit of normal) for girls: −0.17 (1.10; 9.1%, 5.4%); for boys: 0.03 (1.11; 7.2%, 7.5%)]. Conclusions: GLI-African-American FEV1 equations are suitable for benchmarking ePFM-measured FEV1 of school-age children in Lagos, Nigeria; local and foreign PEF equations appear unsuitable, justifying development of new local ePFM-measured PEF equations.