Breathlessness during induced lung hyperinflation in asthma: the role of the inspiratory threshold load.

The effects of the inspiratory threshold load (ITL) on breathlessness and ventilatory mechanics during acute bronchoconstriction were studied by comparing responses to continuous positive airway pressure (CPAP) and inspiratory positive airway pressure (IPAP) in 12 asthmatic subjects after methacholine bronchoprovocation to a maximum change (delta) in FEV1 of 50%. At maximum response, "optimal CPAP" (CPAPOPT) was selected as the level of CPAP providing maximum subjective improvement in breathlessness. Spirometry, breathing pattern, esophageal pressure (Pes), and operational lung volumes were monitored. At maximum response, FEV1 decreased by 54 +/- 3% (mean +/- SEM) (p < 0.001), dynamic end-expiratory volume (EELVdyn) increased 66 +/- 8%, by 1.4 +/- 0.2 L (p < 0.001), and subjects reported severe breathlessness (Borg Scale = 5.6 +/- 0.8). CPAPOPT (5.3 +/- 0.6 cm H2O) significantly (p < 0.001) reduced breathlessness (delta Borg Scale = -3.0 +/- 0.5) and did not cause further dynamic hyperinflation. CPAPOPT r...