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Coupling between triangularis sterni and parasternals during breathing in dogs.
Journal of Applied Physiology (Bethesda, Md. : 1985)
|August 1, 1986
Summary
Quiet breathing involves active muscle coupling. The parasternal intercostals and triangularis sterni muscles work together, with the triangularis sterni actively shortening during exhalation, challenging traditional views of passive muscle length determination.
Area of Science:
- Respiratory Physiology
- Muscle Physiology
Background:
- The mechanics of quiet breathing are traditionally attributed to passive forces.
- The role of specific intercostal muscles in expiratory muscle activity is not fully elucidated.
Purpose of the Study:
- To investigate the functional coupling between parasternal intercostals and triangularis sterni muscles during resting breathing.
- To determine if rib cage muscle length during the expiratory pause is passively determined.
Main Methods:
- Measurement of electrical activity and muscle length changes in parasternal intercostals and triangularis sterni.
- Experiments conducted on 13 supine anesthetized dogs.
- Muscle length changes were referenced to their in situ relaxation length (Lr).
Main Results:
- Parasternal intercostals shortened during inspiration, passively stretching the triangularis sterni.
- Triangularis sterni actively shortened post-inspiration, forcibly stretching parasternal intercostals.
- This pattern persisted after phrenicotomy, indicating a non-diaphragmatic mechanism.
Conclusions:
- Rib cage muscle length during the expiratory pause is actively determined, not passive.
- Parasternal intercostals and triangularis sterni exhibit functional coupling during quiet breathing.
- Findings challenge the conventional understanding of expiratory muscle mechanics.