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Trapped gas and airflow limitation in children with cystic fibrosis and asthma
Author(s) -
Desmond Katharine J.,
Coates Allan L.,
Martin James G.,
Beaudry Pierre H.
Publication year - 1986
Publication title -
pediatric pulmonology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.866
H-Index - 106
eISSN - 1099-0496
pISSN - 8755-6863
DOI - 10.1002/ppul.1950020303
Subject(s) - medicine , asthma , cystic fibrosis , functional residual capacity , plethysmograph , spirometry , lung volumes , respiratory disease , ventilation (architecture) , cardiology , lung , anesthesia , mechanical engineering , engineering
Trapped gas (TG) has been shown to be present in cystic fibrosis (CF) and asthma, but its relationship with airflow limitation (AL) has not been explored. TG was defined as the difference between the functional residual capacity measured by body plethysmography [FRC(BP)] and that measured by helium dilution [FRC(He)] expressed as a percentage of total lung capacity (TLC). We studied 21 children with CF and 15 with asthma who had a similar degree of AL and hyperinflation, however the children with CF had greater amounts of TG compared with asthma [15% ± 2 (mean ± 1SE) vs 8 ± 2, P < 0.05]. Mixing efficiency (ME), an index of the distribution of ventilation, was found to be lower in the CF children than in those with asthma (34 ± 4 vs 54 ± 4). In CF, TG correlated with forced expiratory flow between 25 and 75% of vital capacity (FEF25‐75), ME, RV/TLC, and maximal expiratory flow rates at 25 and 50% of vital capacity (V̇max25 and 50, respectively; r = −0.66, −0.61, 0.72, −0.71, −0.74). ME also correlated with the above measures. In asthma, TG did not correlate with the FEF25‐75, ME, RV/TLC, V̇max25, or V̇max50. Furthermore, TG was frequently found in patients with asthma with moderate AL while it was often absent in patients with severe AL. For both CF and asthma, neither the severity of AL nor the magnitude of the TG could be predicted from the increase in V̇max 50 with helium (ΔV̇50). In CF, TG and ME correlated, thus allowing for an assessment of the validity of FRC(He) in determining hyperinflation. In asthma, the presence or absence of TG could not be anticipated from tests of ME or AL, and hence the validity of FRC(He) in determining hyperinflation could not be anticipated.