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Background In children, obesity typically reduces functional residual capacity (FRC), which reduces airway caliber and increases airway resistance. Whether these obesity‐related changes in respiratory function can alter bronchodilator responsiveness is unknown. Objective To investigate bronchodilator responsiveness in nonasthmatic children with and without obesity. Methods Seventy nonasthmatic children, 8−12 years old, without (n = 19) and with (n = 51) obesity, completed spirometry, impulse oscillometry, and airway resistance measurements through plethysmography pre/post 360 µg of inhaled albuterol. FRC was assessed pre albuterol. A two‐way analysis of variance determined the effects of obesity (group) and inhaled albuterol (pre−post) on outcome measures. Results FRC (%total lung capacity) was 16% lower in children with obesity compared with those without obesity. There was no significant group by pre−post albuterol interaction on any outcome variables. Albuterol inhalation reduced total, central and peripheral airway resistance and increased airway reactance (i.e., less negative) to a similar degree in children with and without obesity. In children with obesity, airway resistance was increased whether measured by impulse oscillometry or plethysmography. However, once airway resistance was adjusted for lung volumes (i.e., specific airway resistance or sRaw), there were no differences between children with and without obesity. In addition, significant but moderate associations were detected between chest mass and FRC (r = −0.566; p < 0.001), FRC and total airway resistance (i.e., Raw; r = −0.445; p < 0.001). Conclusions In nonasthmatic early pubescent children, obesity increases total, central, and peripheral respiratory system resistance. However, the added respiratory system resistance and low lung volume breathing with obesity are not sufficient to reduce bronchodilator responsiveness.

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IntroductionThe purpose of this study was to examine whether maximal oxygen uptake (V̇O2max) prediction equations based on lean body mass can overcome the confounding effect of fat mass on quantification of cardiorespiratory fitness in children with obesity.MethodsForty‐nine children (23 with obesity; BMI ≥ 95th percentile) completed a dual‐energy x‐ray absorptiometry scan for estimating body composition and incremental maximal and verification exercise tests till volitional exhaustion for estimating V̇O2max. Prediction equations based on lean body mass (LBM) and body mass from Cooper D.M. et al 2016 were used to predict V̇O2max [Boys: (0.059 × LBM) − 0.103; (0.052 × body mass) − 0.266. Girls: (0.055 × LBM)–0.187; (0.037 × body mass) + 0.022].ResultsIn children without obesity, predicted V̇O2max based on body mass was 100 ± 10mL/min higher than predicted V̇O2max based on LBM (P < 0.001). In children with obesity, predicted V̇O2max based on body mass was 906 ± 33mL/min higher than predicted V̇O2max based on LBM (P < 0.001). Predicted V̇O2max based on body mass was more strongly associated with fat mass (r = 0.81) compared with predicted V̇O2max based on LBM (r = 0.51); P<0.001. The V̇O2max vs. LBM slope was similar for children with (0.040 L·min−1·kg−1) and without obesity (0.043 L·min−1·kg−1). Percent predicted V̇O2max based on LBM was 13% lower in children with obesity compared with children without obesity (P < 0.001). Percent predicted V̇O2max based on body mass was 37% lower in children with obesity compared with children without obesity (P < 0.001).ConclusionsReferencing V̇O2max to body mass substantially underestimates cardiorespiratory fitness in children with obesity due to the confounding effect of metabolically inactive fat mass. It would be prudent to measure LBM and reference V̇O2max to LBM for a less biased estimation of cardiorespiratory fitness in children with obesity.Support or Funding InformationThis research was supported by NIH R01 HL136643, Texas Health Presbyterian Hospital Dallas, King Charitable Foundation Trust, and unrestricted funds from Dr. Pepper Snapple.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

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