title: Short-term variability in respiratory impedance and effect of deep breath in asthmatic and healthy subjects with airway smooth muscle activation and unloading.
abstract: Inspiratory resistance (RINSP) and reactance (XINSP) were measured for 7 min at 5 Hz in 10 subjects with mild asymptomatic asthma and 9 healthy subjects to assess the effects of airway smooth muscle (ASM) activation by methacholine (MCh) and unloading by chest wall strapping (CWS) on the variability of lung function and the effects of deep inspiration (DI). Subjects were studied at control conditions, after MCh, with CWS, and after MCh with CWS. In all experimental conditions XINSP was significantly more negative in subjects with asthma than in healthy subjects, suggesting greater inhomogeneity in the former. However, the variability in both RINSP and XINSP was increased by either ASM activation or CWS, without significant difference between groups. DI significantly reversed MCh-induced changes in RINSP both in subjects with asthma and healthy subjects, but XINSP in the former only. This effect was impaired by CWS more in subjects with asthma than in healthy subjects. The velocity of RINSP and XINSP recovery after DI was faster in subjects with asthma than healthy subjects. In conclusion, these results support the opinion that the short-term variability in respiratory impedance is related to ASM tone or operating length, rather than to the disease. Nevertheless, ASM in individuals with asthma differs from that in healthy individuals in an increased velocity of shortening and a reduced sensitivity to mechanical stress when strain is reduced.
authors.affiliation: TBM Lab, Dipartimento di Elettronica, Informazione e Bioingegneria, Politecnico di Milano, Milano, Italy;
authors.forename: Alessandro
authors.initials: A
authors.lastname: Gobbi
authors.forename: Riccardo
authors.initials: R
authors.lastname: Pellegrino
authors.forename: Carlo
authors.initials: C
authors.lastname: Gulotta
authors.forename: Andrea
authors.initials: A
authors.lastname: Antonelli
authors.forename: Pasquale
authors.initials: P
authors.lastname: Pompilio
authors.forename: Claudia
authors.initials: C
authors.lastname: Crimi
authors.forename: Roberto
authors.initials: R
authors.lastname: Torchio
authors.forename: Luca
authors.initials: L
authors.lastname: Dutto
authors.forename: Paolo
authors.initials: P
authors.lastname: Parola
authors.forename: Raffaele L
authors.initials: RL
authors.lastname: Dellacà
authors.forename: Vito
authors.initials: V
authors.lastname: Brusasco
mesh_terms: D000328:Adult; D000403:Airway Resistance / Q000187:drug effects / Q000502:physiology; D001249:Asthma / Q000503:physiopathology*; D001980:Bronchi / Q000187:drug effects / Q000502:physiology* / Q000503:physiopathology*; D017097:Electric Impedance; D006801:Humans; D016210:Methacholine Chloride / Q000494:pharmacology; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology* / Q000503:physiopathology*
chemical_list: D016210:Methacholine Chloride
keywords: chest wall strapping; deep inspiration; induced bronchoconstriction; respiratory reactance; respiratory resistance