Relationship between the Ability to Detect Added Resistance at Rest and Breathlessness during Bronchoconstriction in Asthmatics

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Abstract
The ability to detect added resistance at rest was compared to the magnitude of breathlessness (evaluated by a modified Borg scale) during bronchoconstriction in 27 stable asthmatics. Threshold for resistive load detection was analyzed in terms of the Weber fraction (ΔR/R₀) and mouth pressure (P) at the threshold. Bronchoconstriction was induced by inhalation of aerosolized acetylcholine. Both ΔR/R₀ and P correlated inversely with the Borg score during bronchoconstriction (r = -0.537 and r = -0.689, respectively; p < 0.01). On the other hand, during bronchoconstriction the Borg score did not correlate with increased lung volume, acute changes in arterial blood gas composition and drive and timing component of ventilation during bronchoconstriction, although bronchoconstriction caused significant changes in these variables. These results indicate that central processing of afferent stimuli rather than peripheral sensor contribute both to the ability to detect added resistance at rest and to the magnitude of breathlessness during bronchoconstriction in asthmatics