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Effects of long-term continuous respiratory resistive loading on rat diaphragm function and structure
D J Prezant1, T K Aldrich, B Richner
1Department of Medicine, Albert Einstein College of Medicine, Montefiore Medical Center, Bronx, New York 10467.
Journal of Applied Physiology (Bethesda, Md. : 1985)
|March 1, 1993
Summary
Chronic respiratory resistive loading in rats increased diaphragm endurance and muscle mass by altering fiber types. The diaphragm adapted to long-term breathing challenges by enhancing endurance over peak tension.
Area of Science:
- Physiology
- Respiratory Mechanics
- Muscle Adaptation
Background:
- Chronic respiratory loading is a significant physiological stressor.
- Understanding diaphragm adaptation is crucial for respiratory health.
- Previous research has not fully elucidated the long-term effects on diaphragm function and structure.
Purpose of the Study:
- To investigate the long-term effects of continuous respiratory resistive loading on diaphragm mass, contractility, fatigue, and fiber type composition in male rats.
- To determine how the diaphragm adapts to chronic increases in breathing resistance.
Main Methods:
- Male rats were subjected to extratracheal banding to create chronic respiratory resistance for 24-28 weeks.
- Diaphragm mass, surface area, and isometric contractility were measured.
- In vitro diaphragm costal strip preparations were used to assess fatigue resistance and contractility.
- Fiber type analysis was performed.
Main Results:
- Respiratory loading reduced tracheal diameter by 57% and increased diaphragm mass and surface area by 19%.
- Baseline tensions at low frequencies decreased, while fatigue resistance indexes significantly increased.
- These functional changes correlated with an increase in type I (high-endurance) muscle fibers.
Conclusions:
- The diaphragm adapts to chronic resistive loads by increasing its endurance capacity at the expense of peak tension.
- This adaptation involves a shift towards a higher proportion of type I muscle fibers.
- These findings provide insights into the plasticity of respiratory muscles under sustained stress.