1638 PERIPHERAL AIRWAYS DISEASE (PAD) IN ASYMPTOMATIC CHILDREN WITH ASTHMA

Abstract

We have frequently detected maldistribution of ventilation in asymptomatic children with asthma by using the single breath oxygen test (SBO₂). We hypothesized that this results from chronic PAD since there is histologic evidence that PAD occurs in asthma. To test this we compared the slope of the alveolar plateau of the SBO₂ to two indices of PAD: 1) density dependence (DD) of maximum expiratory flow (ΔVmax50VC after breathing He-O₂) and 2) ratio of residual volume to total lung capacity (RV/TLC) by plethysmograph in 28 asthmatic children aged 6-18 years. We found that all children with slopes in our normal range had normal DD and there was no correlation between slope and flow obstruction (MMEF range 42-121% predicted). The children with steep slopes (>2SD) had markedly reduced DD and elevated RV/TLC confirming the presence of PAD; MMEF was very low and they were hospitalized five times more frequently during the previous year (H/YR). Table shows means±SD.

Although tests of expiratory flow obstruction are traditionally used to assess chronicity of asthma, we show that a test of distribution, the SBO₂, will help identify a more severe group with PAD. This group may have a worse long-term prognosis and therefore requires a different therapeutic approach.

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