Volume history and effect on airway reactivity in infants and adults.
Volume history is an important determinant of airway responsiveness. In healthy adults undergoing airway challenge, deep inspiration (DI) provides bronchodilating and bronchoprotective effects; however, the effectiveness of DI is limited in asthmatic adults. We hypothesized that, when assessed under similar conditions, healthy infants have heightened airway reactivity compared with healthy adults and that the effectiveness of DI is limited in infants. We compared the effect of DI on reactivity by using full (DI) vs. partial (no DI) forced-expiratory maneuvers on 2 days in supine, healthy nonasthmatic infants (21) and adults (10). Reactivity was assessed by methacholine doses that decreased forced expiratory flow after exhalation of 75% forced vital capacity during a full maneuver and maximal expiratory flow at functional residual capacity during a partial maneuver by 30% from baseline. Reactivity in adults increased when DI was absent, whereas infants' reactivity was unchanged. Infants were more reactive than adults in the presence of DI; however, adult and infant reactivity was similar in its absence. Our findings indicate that healthy infants are more reactive than adults and, like asthmatic adults, do not benefit from DI; this difference may be an important characteristic of airway hyperreactivity.
Department of Pediatric Pulmonology and Critical Care, Riley Hospital for Children, Indiana University Medical Center, Indianapolis, Indiana 46202, USA.
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Weist
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Williams
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Kisling
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D000328:Adult; D000375:Aging / Q000502:physiology*; D001985:Bronchial Provocation Tests; D016085:Bronchoconstrictor Agents; D002675:Child, Preschool; D005260:Female; D005540:Forced Expiratory Flow Rates; D006801:Humans; D007223:Infant; D008168:Lung / Q000502:physiology*; D008176:Lung Volume Measurements; D008297:Male; D008499:Medical Records; D016210:Methacholine Chloride; D008875:Middle Aged; D012016:Reference Values; D015656:Respiratory Mechanics
D016085:Bronchoconstrictor Agents; D016210:Methacholine Chloride