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Expiratory muscle fatigue in normal subjects
1First Department of Internal Medicine, Yokohama City University School of Medicine, Japan.
Journal of Applied Physiology (Bethesda, Md. : 1985)
|June 1, 1991
Summary
Expiratory resistive loading can cause fatigue in both expiratory and inspiratory muscles. This fatigue, particularly in expiratory muscles, is linked to increased workload during breathing exercises.
Area of Science:
- Respiratory Physiology
- Exercise Physiology
Background:
- Expiratory muscle fatigue is a significant factor in respiratory impairment.
- Understanding the impact of resistive loading on respiratory muscles is crucial for clinical applications.
Purpose of the Study:
- To investigate the effects of expiratory resistive loading on respiratory muscle fatigue in healthy individuals.
- To assess changes in respiratory muscle strength and electrical activity during and after loaded breathing.
Main Methods:
- 11 healthy subjects performed expiratory resistive breathing until exhaustion or 60 minutes.
- Respiratory muscle strength was measured via maximum static expiratory and inspiratory mouth pressures (PEmax and PImax).
- Electromyogram (EMG) frequency power ratio of the rectus abdominis and transdiaphragmatic pressure were monitored.
Main Results:
- Higher expiratory resistance led to significant decreases in PEmax and PImax, persisting for over 60 minutes.
- A progressive decrease in the EMG high-to-low frequency power ratio of the rectus abdominis was observed.
- Transdiaphragmatic pressure increased significantly during loaded breathing.
Conclusions:
- Expiratory resistive loaded breathing induces fatigue in both expiratory and inspiratory muscles.
- Expiratory muscle fatigue is directly related to the high workload imposed by the resistance.
- Inspiratory muscle fatigue may result from increased work due to shortened inspiratory time.