How does bmi status influence spirometry and respiratory muscle strength in children?

Introduction: While BMI correlates positively with spirometry during childhood, young children who are overweight or obese have been shown to have a reduced FEV1/FVC compared to their peers (1). In childhood, obesity has been shown to have a negative effect upon inspiratory muscle strength (2). Aims: To assess whether there are differences in spirometry of children of varying BMI status and whether this relates to respiratory muscle strength. Methods: Within schools, we measured each child’s height, weight, and spirometry. Respiratory muscle strength was assessed via maximal inspiratory and expiratory pressures (MIP/MEP). The child breathed through a pneumotachograph attached to a shutter. To measure MIP, the child exhaled maximally and the shutter was activated. The child made an inspiratory effort against the shutter and peak pressure was recorded. The test was repeated several times. Measurements of MEP were similar, except that the child inhaled maximally and then made a forceful expiratory effort. We calculated BMI and grouped children by centile score into underweight, healthy, overweight or obese, using epidemiological cut-offs (4). Results were adjusted for age and height via an ANCOVA. Results: We studied 297 children (5-11yr). We obtained data for spirometry in 258, MIP in 231 and MEP in 262. Mean adjusted values are shown (Table). All individual parameters showed significant positive correlation with BMI, while FEV1/FVC was significantly negatively correlated with BMI. The obese group had a significantly greater adjusted mean value for MEP than the healthy group and a significantly greater mean adjusted value for FVC than the underweight group, while having a significantly lower mean adjusted FEV1/FVC than both healthy and underweight groups. Conclusion: Despite having the greatest adjusted mean value for expiratory muscle strength and vital capacity, the obese group demonstrated the lowest adjusted mean FEV1/FVC, indicating a potential alteration in respiratory flow dynamics for children of greater BMI. 1. Tantisira et al, Thorax. 2003 Dec;58(12):1036-41. 2. da Rosa et al, Rev Paul Pediatr. 2014 Jun;32(2):250-5. Underweight Healthy Overweight Obese FEV1 (L) 1.55 1.69 1.69 1.67 FVC (L) 1.70 1.90 1.94 1.97 FEV1/FVC (%) 91.2 89.1 87.7 85.7 MIP (kPa) 6.89 7.07 7.68 7.57 MEP (kPa) 6.01 6.29 6.54 7.12