Lung mechanical properties distinguish children with asthma with normal and diminished lung function.

Background: Children with asthma, even those with severe persistent disease, can have forced expiratory volume in 1 second (FEV ₁ ) values ≥100% of predicted, while others have diminished FEV ₁ .
Objective: We sought to characterize the lung mechanical properties underlying these two asthma phenotypes and the mechanisms explaining the paradox of severe asthmatic children, whom when clinically stable can have an FEV ₁ >100% of predicted, but during an acute bronchospastic episode can experience a life-threatening asthma event.
Methods: Lung mechanics were evaluated in three groups of children: asthmatics with FEV ₁ ≥100% (HFEV ₁ ; n = 13), asthmatics with FEV ₁ ≤80% (LFEV ₁ ; n = 14) and non-asthmatic controls (n = 10). A linear mixed model was used to examine the relationship between volume and static transpulmonary pressures obtained at total lung capacity (TLC); actual TLC %of predicted and flow; and static transpulmonary pressure and flow.
Results: HFEV ₁ asthmatics had larger airways (FEV ₁ z-scores 1.12 vs -2.37; P < .05), greater lung volumes (mean % of predicted TLC 134.8% vs 109.6%; P < .05) and lower airway resistance (mean %of predicted Raw 101.9% vs 199.9%; P < .05) compared to the LFEV ₁ group. Moreover, HFEV ₁ asthmatics had significantly reduced elastic recoil pressure (pressure-volume curve shifted upward and to the left) and higher lung compliance (0.21 vs 00.9 L/cm H ₂ O; P < .05) compared to the LFEV ₁ group. The pressure-flow curves revealed the LFEV ₁ group to have significantly increased resistance to flow in the upstream segment of the airways at all lung volumes studied compared to HFEV ₁ .
Conclusion and Clinical Relevance: HFEV ₁ asthmatic children display distinct lung mechanical proprieties compared to their LFEV ₁ asthmatic peers. With loss of elastic recoil pressure, the HFEV ₁ group could generate normal FEV ₁ due to proportionally enlarged airways and reduced airway resistance, while airflow limitation in the LFEV ₁ is due to increased airway resistance. Loss of elastic recoil and interdependence during acute bronchoconstriction episodes may predispose the HFEV ₁ group to catastrophic reductions in airflow.
(© 2020 John Wiley & Sons Ltd.)