Role of body mass index in unbalanced (dysanaptic) lung growth of healthy infants.

Rationale: Imbalance between forced expiratory volume in the first second (FEV) and forced vital capacity (FVC) (dysanapsis) has been reported in children who are obese. This dysanaptic growth might begin at an early age, although there are no data on children younger than 6 years.

Objetives: To assess whether body mass index (BMI) and early weight gain, in healthy infants born at term, plays a significant role in the imbalance between FEV and FVC, even in the absence of obesity.

Methods: Lung function was measured by means of raised volume rapid thoracic compression in 69 healthy infants born at term from the Nutrition in Early Life and Asthma cohort. Dysanapsis was defined as zFVC >0.674, zFEV ≥-1.645, and FEV /FVC ≤-1.645. Weight gain (g/day) and growth rate (cm/year) were calculated as the difference between weight and length on the test date and those at birth. To assess the relationship between zBMI and dysanapsis, a receiver operating characteristic curve was performed. Multivariable analysis was carried out by means of linear regressions (one for each lung function index) and by logistic regression for dysanapsis (yes/no).

Results: Higher zBMI was associated with risk of dysanapsis (odds ratio: 3.53, [95% confidence interval: 1.30; 9.66]; p = .014): Each additional zBMI unit was associated with ~10 mL higher FVC and with ~3.5% lower FEV/FVC. Weight gain was associated with lower FEV/FVC ratio.

Conclusion: Dysanaptic development of lung function begins very early in infancy and is related with weight gain and body mass index, even in the absence of obesity.