Maximal flow at functional residual capacity in asthmatic preschool children

Background: Many preschool children will perform correct peak-flow but will not exhale to residual volume, thus limiting the determination of airways obstruction. The maximal flow measured at function residual capacity (V’maxFRC) is independent of lung empting and could potentially serve as a parameter for describing flow at low lung volumes. The study determines the detection of airway obstruction/dilation in asthmatic preschool children by V’maxFRC, compared to FEV1 and FEF25-75. Methods: Children performed bronchial provocation test (BPT; n?=?26) or received bronchodilators (Post-BD; n?=?31). V’maxFRC was extracted at inspiratory capacity point of flow/volume maneuvers. The %change of V’maxFRC from baseline was compared with changes in various spirometry indices and to values obtained from our previously studied healthy control children. Results: FEV1, FEF25-75, and V’maxFRC decreased by 30.9?±?12.2%, 46.2?±?10.9%, and 36.6?±?8.0%, respectively, while FRC increased by 37.0?±?24.9% at end of the BPT. Post-BD spirometry values increased by 17.1?±?16.1%, 47.0?±?42.2, and 45?±?24%, respectively (p?<?0.0001). A positive response to bronchodilators was observed in 15/31 (48%) children by FEV1, in 22/31 (71%) children by V’maxFRC, and in 21/31 children by FEF25-75. Conclusion: V’maxFRC detects airway obstruction/dilation in young asthmatic children similar to FEF25-75 and FEV1. V’maxFRC may be a valuable index in preschool children who cease exhalation prematurely. Digitally measured V’maxFRC should confirm the actual values in a wider age range in healthy and disease states.