The increase of residual volume (RV) was investigated during acute bronchoconstriction induced in healthy subjects by methacholine (MCh) (Group 1, n = 13) and in asthmatics by MCh (Group 2, n = 21), or housemite dust (Group 3, n = 11) during early and late airway responses (EAR and LAR), or a series of deep breaths (Group 4, n = 7). In all subjects the difference between residual volume after partial (RVp) and maximal maneuver (RV), expressed as a percentage of control FVC, increased during bronchoconstriction and was correlated with the percent increase of maximal to partial flow ratio at 50% of control FVC (M/P50) (r = 0.854, p < 0.0001). At comparable reduction of partial expiratory flow at 50% of control FVC (VP50), the decreases of FEV1 and FVC were less in healthy than asthmatic subjects, whereas the change of FEV1/FVC was similar in all groups, reflecting similar change in slope of flow-volume curves. The increase of RVp was similar in all groups (range: 15 to 19%), but the increase of RV was 6 +/- 1% (SEM) in healthy subjects and significantly greater (range: 11.1 to 13.3%) in all groups of asthmatics (p < 0.02, analysis of variance [ANOVA]). The effect of deep inhalation (DI) on the airway caliber as assessed by the increase of M/P50 was higher in normal subjects than in all groups of asthmatics (p < 0.0001). A negative correlation was found between the increases of RV and M/P50 in all groups (r = -0.358, p < 0.01), suggesting that healthy subjects had a limited increase of RV because of a marked bronchodilator effect of DI.(ABSTRACT TRUNCATED AT 250 WORDS)
