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Airway hyperresponsiveness, remodeling, and smooth muscle mass: right answer, wrong reason?
Madavi N Oliver1, Ben Fabry, Aleksandar Marinkovic
1Physiology Program, Department of Environmental Health, Harvard School of Public Health, Boston, Massachusetts, USA.
American Journal of Respiratory Cell and Molecular Biology
|April 28, 2007
Summary
Airway remodeling in asthma causes airway smooth muscle (ASM) to shorten excessively. Increased ASM mass, not just airway thickening, impairs deep inspiration relaxation, contributing to asthma symptoms.
Area of Science:
- Respiratory Physiology
- Pulmonary Medicine
- Smooth Muscle Biology
Background:
- Airway remodeling is a hallmark of asthma.
- Airway smooth muscle (ASM) hyperresponsiveness contributes to asthma pathophysiology.
- The precise role of increased ASM mass in airway remodeling and function remains debated.
Purpose of the Study:
- To quantify the impact of airway wall remodeling on ASM shortening.
- To investigate the functional consequences of increased ASM mass and airway thickening.
- To elucidate the mechanisms behind impaired bronchodilation during deep inspirations in asthma.
Main Methods:
- Isolated sheep ASM was subjected to controlled loading simulating airway wall changes.
- ASM length was measured under varying conditions of airway geometry, elasticity, and transpulmonary pressure.
- The effects of thickening individual airway wall compartments (smooth muscle, submucosal, adventitial) were assessed.
Main Results:
- Simulated asthmatic airways with thickened compartments showed significantly greater ASM shortening.
- Increased ASM mass alone led to the most pronounced muscle shortening.
- ASM in asthmatic airways failed to lengthen during deep inspirations, unlike normal airways.
Conclusions:
- Increased ASM mass is the primary driver of functional derangements in asthmatic airways.
- This increased mass explains both hyperresponsiveness and the failure of deep inspirations to relax the airway.
- The mechanisms underlying ASM shortening and impaired relaxation differ from previous assumptions.
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