Analysis of time course and magnitude of lung inflation effects on airway tone: relation to airway reactivity.

Abstract

Lung inflation transiently reverses methacholine constriction of airways in normal subjects, whereas this capacity is diminished in subjects with airway hyperreactivity. To explore the mechanisms underlying these differences, we examined the magnitude and time course of the effects of lung inflation in subjects with varying degrees of methacholine responsiveness. Ten subjects were defined as nonreactive (NR) and 9 subjects as reactive (R) on the basis of the FEV1 decrement evoked during graded methacholine challenge. To examine the effects of inflation, Plethysmographic specific airway conductance (SGaw) was first measured before and after an inhaled methacholine dose titrated to produce a 60% fall in SGaw. Subjects then inspired maximally to total lung capacity, and SGaw was remeasured 7, 15, 30, 45, and 60 s after inflation. An increase in SGaw was observed at 7 s and, thereafter, it declined nonlinearly with time toward preinflation values. Measured SGaw values after inflation were fitted to a single e...