Smooth muscle in human bronchi is disposed to resist airway distension.
Studying airway smooth muscle (ASM) in conditions that emulate the in vivo environment within which the bronchi normally operate may provide important clues regarding its elusive physiological function. The present study examines the effect of lengthening and shortening of ASM on tension development in human bronchial segments. ASM from each bronchial segment was set at a length approximating in situ length (Linsitu). Bronchial tension was then measured during a slow cyclical strain (0.004Hz, from 0.7Linsitu to 1.3Linsitu) in the relaxed state and at graded levels of activation by methacholine. In all cases, tension was greater at longer ASM lengths, and greater during lengthening than shortening. The threshold of methacholine concentration that was required for ASM to account for bronchial tension across the entire range of ASM lengths tested was on average smaller by 2.8 logs during lengthening than during shortening. The length-dependency of ASM tension, together with this lower threshold of methacholine concentration during lengthening versus shortening, suggest that ASM has a greater ability to resist airway dilation during lung inflation than to narrow the airways during lung deflation. More than serving to narrow the airway, as has long been thought, these data suggest that the main function of ASM contraction is to limit airway wall distension during lung inflation.
Institut Universitaire de Cardiologie et de Pneumologie de Québec (IUCPQ), Université Laval, Québec, Canada.
Morgan
M
Gazzola
Institut Universitaire de Cardiologie et de Pneumologie de Québec (IUCPQ), Université Laval, Québec, Canada.
Cyndi
C
Henry
Institut Universitaire de Cardiologie et de Pneumologie de Québec (IUCPQ), Université Laval, Québec, Canada.
Christian
C
Couture
Institut Universitaire de Cardiologie et de Pneumologie de Québec (IUCPQ), Université Laval, Québec, Canada.
David
D
Marsolais
Woolcock Institute of Medical Research, Australia; University of Sydney, Australia; CRC for Asthma, Sydney, Australia.
Gregory G
GG
King
Department of Environmental Health, Harvard T.H. Chan School of Public Health, Boston, United States.
Jeffrey J
JJ
Fredberg
Institut Universitaire de Cardiologie et de Pneumologie de Québec (IUCPQ), Université Laval, Québec, Canada. Electronic address: ynuk.bosse@criucpq.ulaval.ca.
Ynuk
Y
Bossé
D000368:Aged; D001696:Biomechanical Phenomena; D001980:Bronchi / Q000187:drug effects / Q000473:pathology / Q000502:physiology* / Q000601:surgery; D016085:Bronchoconstrictor Agents / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D008176:Lung Volume Measurements; D008297:Male; D016210:Methacholine Chloride / Q000494:pharmacology; D008875:Middle Aged; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D009130:Muscle, Smooth / Q000187:drug effects / Q000473:pathology / Q000502:physiology* / Q000601:surgery; D009369:Neoplasms / Q000601:surgery; D012119:Respiration
D016085:Bronchoconstrictor Agents; D016210:Methacholine Chloride
Contractile capacity; Human bronchi; Hysteresis; Intrinsic tone; Oscillatory mechanics