Effect of deep inspiration on airway conductance in subjects with allergic rhinitis and allergic asthma.

We measured specific airway conductance (Gaw/Vtg) in a body plethysmograph before and after a deep inspiratory maneuver in 8 subjects with allergic rhinitis and 8 subjects with allergic asthma. In hay fever subjects deep inspiration had no effect on Gaw/Vtg if it was performed in the control state; however, when methacholine-induced bronchoconstriction was present, deep inspiration transiently increased Gaw/Vtg. In asthmatic subjects deep inspiration was followed by a transeint fall in baseline Gaw/Vtg in the control state; however, when bronchoconstriction was present, deep inspiration was followed by small and variable changes in Gaw/Vtg in 7 subjects and marked improvement in Gaw/Vtg in 1 subject. In asthmatic subjects the bronchoconstrictor response to deep inspiration performed in the control state is thought to be due to reflex changes in bronchomotor tone mediated by cholinergic (vagal) nerve pathways. Like asthmatic subjects, hay fever subjects, hay fever subjects also possess cholinergic-mediated airway hyperreactivity compared with normals. Our results indicate that, in spite of their increased airway reactivity, hay fever subjects respond more like normal subjects than like asthmatic subjects after a deep inspiratory maneuver.