Inhaled Albuterol Increases Forced Mid-expiratory Flows In Non-asthmatic Children With And Without Obesity

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PURPOSE: The effect of albuterol on β2-adrenoceptor activation is usually assessed by a significant increase in forced expiratory volume in one second (FEV1). However, even without a significant increase in FEV1, an increase in isovolume forced expiratory flow between 25% and 75% (isoFEF25-75) of forced vital capacity (FVC) would allow for greater exercise tidal flow rates thus increasing ventilatory capacity (V̇Ecap). This could be particularly important in children with obesity, who breathe at low lung volumes and have limited expiratory reserves. We examined if isoFEF25-75 and V̇Ecap increase with albuterol in non-asthmatic prepubescent children with and without obesity. METHODS: A total of 46 obese (n=29 boys) and 29 nonobese (n=14 boys) children, ages 8-12yr, performed spirometry according to the American Thoracic Society guidelines before and after 360μg of albuterol. Subjects who displayed ≥12% and ≥200mL increase in FEV1 after albuterol were excluded. For each individual, V̇Ecap was determined using an estimated tidal volume at maximal exercise (‘VTmax’ = FVC/2) and forced expiratory time between 25% and 75% of FVC (FET25-75) to estimate an individualized maximum breathing frequency (fbmax), where V̇Ecap = VTmax*fbmax. A two-way ANOVA with repeated measures (obese x nonobese; pre- x post-inhaler) was conducted. RESULTS: No significant group by treatment interaction was detected. No significant differences were detected in spirometry parameters between children with and those without obesity. From pre- to post-inhaler in the total cohort of children (n=75), FVC significantly decreased (-0.70%, p = 0.04). While there was a statistically significant increase in peak expiratory flow (+3.0%, p = 0.02), FEV1 (+2.6%, p < 0.01) and FEV1/FVC (+3.0%, p < 0.01), there were more meaningful increases in isoFEF25-75 (+17.1%, p < 0.01) and V̇Ecap (+15.5%, p < 0.01).CONCLUSIONS: Administration of albuterol can increase isoFEF25-75 despite a relatively small nonclinical increase in FEV1. The remarkable increase in flow rates along the effort-independent portion of a forced expiration yields a large increase in V̇Ecap, which could potentially change breathing mechanics and ventilatory output during heavy exercise in non-asthmatic prepubescent children with and without obesity.