Single breath counting for the evaluation of pediatric respiratory function: derivation of a "normogram"

Single breath counting (SBC) is the measurement of how far an individual can count in cadence with a metronome set at 2 beats per second in a normal speaking voice following a maximal effort inhalation. Previous work has demonstrated that it correlates well with standard measures of pulmonary function. The objective of this study is to derive a "normogram" of healthy children showing the expected SBC value as a function of easily measured physiologic parameters (age, gender, height, and weight). This was a prospective observational study of a convenience sample of healthy children presenting for well-child checks or non-respiratory complaints at a large tertiary care center. Correlation was determined by the Pearson's product correlation coefficient (r) and r (2) determined as a measure of shared variance. Multiple regression analysis was performed on demographic data to determine a best linear fit with calculation of the coefficient of determination (R (2)). A total of 105 children served as the basis for analysis; 54 (51.4 %) were male and average age was 9.7 (median 10, range 3-15) years. For both males and females, height correlated most strongly with SBC score (r = 0.730 and 0.725, respectively). In both genders, height alone accounted for more than 50 % of the observed variance in the results (r (2) = 0.533 and 0.526, respectively). Breath counting, an easy to perform test that appears to correlate well with standard measures of pulmonary function and shows promise for measuring asthma severity in children. We present an equation for predicting normal results (a "normogram").