Relationship between maldistribution of ventilation and airways obstruction in children with asthma

This study was designed to explore the relationship between ventilation non-uniformity, as assessed by moment analysis of nitrogen washout, and airways obstruction, as assessed by spirometry, in children with asthma. Moment ratios derived from the multibreath washout curves in asthmatics were significantly higher than those obtained from healthy controls (P less than 0.001). Among patients with asthma, moment ratios showed a high degree of negative correlations with spirometric variables expressed as percent of predicted, i.e., increasing airways obstruction was associated with increasing ventilation non-uniformity. When the subjects were tested on multiple occasions during one test day the results demonstrated a strong quantitative relationship within subjects between spontaneous changes in moment ratios and spirometric variables (P less than 0.001), with the slope of the regressions showing a trend to vary from one patient to another. Chi squared analysis showed that significant changes in FEV1 were paralleled by corresponding significant changes in moment ratios with a sensitivity of approximately 81% and a specificity of 82%. Additionally, changes in FEV1 induced by an inhaled bronchodilator were associated with concomitant changes in moment ratios. We conclude that: (1) the majority of children with asthma have some degree of ventilation non-uniformity which is correlated with their degree of airways obstruction, and (2) spontaneous changes in airways obstruction in such subjects are paralleled by changes in ventilation non-uniformity.