Effect ofinspiratory flow rateon bronchomotor tone innormal andasthmatic subjects

Theeffect oftheinspiratory flowrateduring deepinspiration on theregulation of bronchomotor tonewas studied inninenormaland22asthmatic subjects. Changesinbronchial tonewere assessed byrespiratory resistance measured byan oscillation method.Innormal subjects withbronchoconstriction induced bymethacholine a rapiddeepinspiration reduced respiratory resistance more than a slowdeepinspiration. Asthmatic subjects withspontaneous airway narrowing showed an increase inrespiratory resistance after deepinspiration that was greaterafter rapid thanafter slowdeepinspiration. On theotherhand,inasthmatics with methacholine induced bronchoconstriction, bronchodilatation occurred after deepinspiration andthis was also greaterafter rapid thanafter slowdeepinspiration. Lignocaine inhalation attenuated bothbronchoconstriction andbronchodilatation induced bybothslowandrapid deep inspiration. Theseresults suggestthat theeffects ofdeepinspiration aremediated atleast inpart viareceptors intheairways. Itissuggested that inasthmatic patients withspontaneousbroncho- constriction irritant receptor activity will beincreased inproportion tothespeedofinspiration. After methacholine induced bronchoconstriction stretch receptoractivity islikely tobehaveina similar fashion, leading toan opposite effect. A deepinspiration hasbeenreported toproduce a transient decrease inairway calibre insomeasthma- ticsubjects.' 2Incontrast, inthepresence ofphar- macologically induced bronchoconstriction adeep inspiration produces bronchodilatation inmost asthmatice andnormal4 subjects. Thereasonfor these divergent effects ofdeepinspiration onbron- chomotor tonewithandwithout druginduced bronchoconstriction isunclear. Deepinspiration might stimulate different vagal sensory receptors in these different circumstances: inthose withartifi- cially induced bronchoconstriction deepinspiration mightstimulate stretch receptors, whichinduce bronchodilatation5; while inasthmatics without pro- vokedbronchoconstriction