Longitudinal lung function growth of Mexican children compared with international studies

Abstract

Introduction: Our aim was to compare the longitudinal lung function growth of Mexican children and adolescents with the collated spirometric reference proposed for international use and with that of Mexican-Americans from the National Health State Examination Survey III (NHANES) III study.

Materials and methods: A cohort of Mexican children in third year of primary school was followed with spirometry twice a year through secondary school. Multilevel mixed-effects lineal models separated by gender were fit for the spirometric variables of 2,641 respiratory-healthy Mexican children expressed as Z-scores of tested reference equations. Impact of adjustment by sitting height on differences with Mexican-American children was observed in a subsample of 1,987 children.

Results: At same gender, age, and height, Mexican children had increasingly higher forced expiratory volume in 1 s (FEV1) and Forced vital capacity (FVC) than the children from the collated reference study (mean Z-score, 0.68 for FEV1 and 0.51 for FVC) and than Mexican-American children (Z-score, 0.23 for FEV1 and 0.21 for FVC) respectively. Differences with Mexican-Americans were not reduced by adjusting by sitting height.

Conclusions: For reasons that remain unclear, the gender-, age-, and height-adjusted lung function of children from Mexico City is higher than that reported by several international studies.

Figure 1. Lung function growth of a cohort of Mexican children compared with international spirometric reference equations.

Forced expiratory volume in 1 s (FEV₁) (panel A), Forced vital capacity (FVC) (panel B), the ratio of FEV₁ and FVC (FEV₁/FVC) (panel C) vs. age in years of children from Mexico City is expressed as Z-score of the international study of lung function by Quanjer et al. (empty diamond), Mexican-American children from the National Health and Nutrition Examination Survey III (NHANES III) study (full triangles), and Mexican children from a cross-sectional study (empty circles). The majority of values for age-, gender-, and height-adjusted FEV₁ and FVC in Mexican children from the reported cohort are positive compared with those of children from international studies and of Mexican-American children, indicating higher spirometric lung function, and these in addition change position during growth relative to predicted values. The better the fit, the closer the median Z-score will be to zero at all ages.

Figure 2. Lung function growth of a cohort of Mexican children as estimated by longitudinal models (full symbols) vs. cross-sectional models (empty symbols).

Forced expiratory volume at 1 s (FEV₁) (panel A), Forced vital capacity (FVC) (panel B), the ratio of FEV₁ and FVC (FEV₁/FVC) (panel C) and Peak expiratory flow (PEF) (panel D) vs. age in years of children from Mexico City as expressed in mL (FEV₁ and FVC) or in percentage (FEV₁/FVC) for mean age, mean height, and mean weight of children, for longitudinal growth (full circles) or cross-sectional models (empty circles). Estimates from the cross-sectional model and the longitudinal model depart during follow-up for FEV₁/FVC, as do the values at the end of follow-up, especially for girls.

Figure 3. Peak expiratory flow (PEF) growth of a cohort of Mexican children compared with the National Health and Nutrition Examination Survey III (NHANES-III) equation.

PEF of children in the cohort expressed as Z-score of the Mexican-American children from the NHANES III study (full triangles, panel A), and Mexican children from a cross-sectional study (empty circles, panel A). Panel B has PEF of Mexican children adjusted to that estimated at sea level. The majority of values for age-, gender- and height-adjusted PEF in Mexican children from the reported cohort are positive compared with those of children among Mexican-American children, and these in addition increase during growth relative to predicted values. Adjusting PEF in Mexico City to sea level values (see Supporting Information) partially reduces the positive bias especially in boys.