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1 Department of Pharmacological and Pharmaceutical Sciences, University of Houston, and 2 Departments of Medicine, Immunology, and Biology of Inflammation Center, and 3 Department of Pediatrics, Baylor College of Medicine, Houston, Texas 77030
Airway dysfunction in asthma is
characterized by hyperresponsiveness, heterogeneously narrowed airways,
and closure of airways. To test the hypothesis that airway constriction
in ovalbumin (OVA)-sensitized OVA-intranasally challenged (OVA/OVA)
mice produces mechanical responses that are similar to those reported
in asthmatic subjects, respiratory system resistance (Rrs) and
elastance (Edyn,rs) spectra were obtained in OVA/OVA and control
mice during intravenous methacholine (MCh) infusions. In control
mice, MCh at 1,700 µg · kg
1 · min
1
produced 1) a 495 and 928% increase of Rrs at 0.5 Hz and
19.75 Hz, respectively, 2) a 33% rise in Edyn,rs at 0.5 Hz,
and 3) a mild frequency (f)-dependent increase of Edyn,rs.
The same MCh dose in OVA/OVA mice produced 1) elevations of
Rrs at 0.5 Hz and 19.75 Hz of 1,792 and 774%, respectively,
2) a 390% rise in Edyn,rs at 0.5 Hz, and 3)
marked f-dependent increases of Edyn,rs. During constriction, the f
dependence of mechanics in control mice was consistent with homogeneous
airway narrowing; however, in OVA/OVA mice, f dependence was
characteristic of heterogeneously narrowed airways, closure of airways,
and airway shunting. These mechanisms amplify the pulmonary mechanical
responses to constrictor stimuli at physiological breathing rates and
have important roles in the pathophysiology of human asthma.
airway closure; resistance; elastance; airway hyperresponsiveness
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