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The impact of mechanical ventilation on immature airway smooth muscle: functional, structural, histological, and
Aaron B Cullen1, Peter H Cooke, Steven P Driska
1Department of Physiology, Temple University School of Medicine, Philadelphia, PA, USA.
Insights
Mechanical ventilation impairs lamb airway function and structure, with effects worsening with age. This ventilator-induced airway injury involves cellular changes and epithelial damage, impacting preterm infant lung development.
Area of Science:
- Neonatal Physiology
- Respiratory Medicine
- Pathology
Background:
- Mechanical ventilation is crucial for preterm infants but can cause airway injury.
- Bronchopulmonary dysplasia and airway dysfunction are common complications.
- The mechanisms underlying ventilator-induced airway injury remain unclear.
Purpose of the Study:
- To investigate the age-related effects of mechanical ventilation on airway function.
- To correlate functional changes with structural alterations at multiple levels (tissue, cellular, ultrastructural, molecular).
- To elucidate the pathogenesis of ventilator-induced airway injury.
Main Methods:
- Tracheal rings from ventilated and non-ventilated lambs (premature and newborn) were studied.
- Functional assessment included passive/active length-tension and dose-response relationships.
- Structural analysis involved smooth muscle cell measurement, light/electron microscopy, and myosin heavy chain isoform analysis.
Main Results:
- Mechanical ventilation decreased passive stiffness and maximal force generation, most notably in newborns.
- Functional deficits correlated with reduced smooth muscle cell length and ultrastructural damage, particularly in older lambs.
- Epithelial denudation occurred at all ages; no significant changes in myosin isoforms were observed.
Conclusions:
- Mechanical ventilation induces age-related changes in tracheal function and structure.
- Pathogenesis involves ultrastructural alterations, reduced cell length, and epithelial damage.
- Findings contribute to understanding ventilator-induced airway injury in vulnerable infants.
Abstract:
Preterm infants exposed to mechanical ventilation often develop airway dysfunction and bronchopulmonary dysplasia. The mechanisms of mechanical ventilation-induced airway injury are currently unknown. This study correlates the age-related effects of mechanical ventilation on airway function with structural alterations at the tissue, cellular, ultrastructural, and molecular levels. Mechanically ventilated and nonventilated tracheal rings were obtained from premature and newborn lambs. In tissue baths, the passive and active length-tension relationships and dose-response characteristics of the tracheal rings were determined. Fixed tracheal rings were digested and the resulting isolated smooth muscle cells measured. Rings were analyzed by light and electron microscopy. Additionally, protein was extracted from the tracheal smooth muscle and myosin heavy chain isoforms were separated by SDS-polyacrylamide gel electrophoresis and analyzed by densitometry. Mechanical ventilation resulted in a significant decrease of both the slope of the passive length-stress relationship and of maximal force generation, with both effects being most pronounced in the newborn age group. These age-related functional alterations correlated with a decrease in smooth muscle cell length and a disruption of ultrastructural architecture, which were also most pronounced in the older groups. Furthermore, mechanical ventilation resulted in epithelial denudation at all ages. There were no acute statistically significant effects of mechanical ventilation on myosin heavy chain isoform expression. This study demonstrates age-related effects of mechanical ventilation on the passive and active characteristics of tracheal function and provides a structural analysis of potential mechanisms. The mechanisms behind these functional differences involve ultrastructural changes in cell length, tissue matrix, and disruption of epithelial integrity. These findings help elucidate the pathogenesis of ventilator-induced airway injury.
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