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Enhanced airway dilation by positive-pressure inflation of the lungs compared with active deep inspiration in patients with asthma

¹Department of Pulmonology, Leiden University Medical Center, Leiden; ²Department of Pulmonology, Medical Center Alkmaar, Alkmaar; and ³Department of Respiratory Medicine, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands

Submitted 20 November 2007 ; accepted in final form 15 September 2008

Deep inspiration temporarily reduces induced airways obstruction in healthy subjects. This bronchodilatory effect of deep inspiration is impaired in asthma. Passive machine-assisted lung inflation may augment bronchodilation compared with an active deep inspiration in patients with asthma by either opening closed airways or by reducing fluid flux across the airway wall during deep inspiration, and thereby increasing the tethering forces on the airway wall. We recruited 24 patients with asthma [18–46 yr old, forced expiratory volume in 1 s (FEV₁) > 70% predicted; provocative concentration of methacholine inducing a 20% fall in FEV₁ (PC₂₀) < 8 mg/ml], with either an impaired (n = 12) or an intact (n = 12) bronchodilatory response to deep inspiration. Two methacholine challenges were performed on separate days. At a 50% increase in respiratory resistance (forced oscillation technique at 8 Hz), the change in resistance by a positive-pressure inflation (computer-driven syringe) or an active deep inspiration was measured in randomized order. The reduction in resistance by positive-pressure inflation was significantly greater than by active deep inspiration in the impaired deep inspiration response group (mean change ± SE: –0.6 ± 0.1 vs. –0.03 ± 0.2 cmH₂O·l^–1·s, P = 0.002). No significant difference was found between positive-pressure inflation and active deep inspiration in the intact deep inspiration response group (–0.6 ± 0.2 vs. –1.0 ± 0.3 cmH₂O·l^–1·s, P = 0.18). Positive-pressure inflation of the lungs can significantly enhance deep inspiration-induced bronchodilation in patients with asthma.

airway narrowing; deep breath; deep inspiration-induced bronchodilation; methacholine; lung inflation