Introduction: Although peak expiratory flow rate is the conventional way to measure asthma severity in adults, its use is problematic in children because it is effort dependent. Forced expiratory volume in 1 second (FEV₁) and the ratio of FEV₁ to forced vital capacity (FEV₁/FVC) are more accurate, but generally not available in the emergency department (ED). A better test is needed. Single-breath counting (SBC) is the measurement of how far an individual can count in a normal speaking voice after a maximal effort inhalation. The count is in cadence to a metronome set at 2 beats per second. Previous work has suggested that SBC correlates with standard measures of pulmonary function in adults. However, it has never been tested in children.
Objectives: The aims of this study are to determine if SBC can be easily performed by children and to assess the correlation between SBC and standard measures of pulmonary function in a pediatric population.
Methods: This was a prospective observational study of a convenience sample of children presenting to the pulmonary clinic for scheduled pulmonary function testing (PFT). Peak expiratory flow rate, FEV₁, FVC, forced expiratory flow 25% to 75%, and FEV₁/FVC were measured and recorded. After PFT, subjects were asked to perform SBC. Three attempts were allowed, and the average was recorded. Correlation was determined by the Pearson coefficient.
Results: Sixty-seven children (ages 5-18 years, 64% male) were enrolled. All were able to understand and complete the testing. Indications for PFT included asthma and/or allergies (n = 44), cystic fibrosis (n = 9), and other chronic diseases (n = 14). The correlations (r) of SBC to peak expiratory flow rate, FEV₁, FVC, forced expiratory flow 25% to 75%, and FEV₁/FVC were 0.55, 0.66, 0.71, 0.44, and -0.29, respectively (P < .05 for all results).
Conclusion: Single-breath counting is easy to perform in children, seems to correlate well with standard measures of pulmonary function, and shows promise for measuring asthma severity in children. Further work to define the range of reference SBC values (as a function of age and/or body size) and an evaluation of the utility of SBC in an ED population of acute asthmatics is indicated.
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