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Mechanical work of breathing during maximal voluntary ventilation
1Meakins-Christie Laboratories, McGill University, Montreal, Canada H2X 2P2.
Journal of Applied Physiology (Bethesda, Md. : 1985)
|July 9, 1998
Summary
Respiratory muscle work capacity was studied during maximal ventilation. Work per breath decreased with frequency, while power peaked around 100 cycles/min, with wasted work increasing at higher frequencies.
Area of Science:
- Respiratory Physiology
- Exercise Physiology
Background:
- Assessing respiratory muscle working capacity is crucial for understanding exercise limitations.
- Maximal voluntary ventilation (MVV) is a common test, but its efficiency at varying frequencies is less understood.
Purpose of the Study:
- To measure the working capacity of respiratory muscles during maximal voluntary ventilation (MVV) across a wide range of respiratory frequencies.
- To quantify wasted work due to alveolar gas compressibility at different breathing rates.
Main Methods:
- Utilized the esophageal balloon technique to measure respiratory muscle work per breath (W) and respiratory power (W).
- Subjects performed MVV at imposed respiratory frequencies (f) from 20 to 273 cycles/min.
- Employed a body plethysmograph to determine wasted work (Wg') from alveolar gas compressibility.
Main Results:
- Work per breath (W) decreased as respiratory frequency (f) increased.
- Respiratory power (W) reached a maximum at approximately 100 cycles/min.
- Wasted work (Wg') was a small fraction of total work at lower frequencies but increased significantly at higher frequencies (8-22% of W at 200 cycles/min).
Conclusions:
- Respiratory muscle efficiency varies with breathing frequency during MVV.
- High respiratory frequencies during MVV lead to a substantial increase in wasted work due to gas compression.
- These findings have implications for understanding respiratory limitations during intense exercise and respiratory disease.