Linkage between parasternals and external intercostals during resting breathing.

Area of Science:

• Respiratory Physiology
• Biomechanics
• Comparative Anatomy

Background:

• The cranial rib cage's mechanical function during breathing involves complex intercostal muscle interactions.
• Understanding the interplay between parasternal and external intercostal muscles is crucial for respiratory mechanics.

Purpose of the Study:

• To investigate the mechanical coupling and functional relationship between parasternal and external intercostal muscles in the cranial rib cage of dogs.
• To determine the relative contributions of these muscles to rib cage elevation during resting inspiration.

Main Methods:

• Measurements of respiratory muscle length changes and electromyograms in spontaneously breathing dogs.
• Selective denervation experiments to isolate the function of parasternal and external intercostal muscles.

Main Results:

• Parasternal intercostals exhibited greater inspiratory shortening than external intercostals.
• Denervation of parasternal muscles abolished inspiratory shortening in both muscle types.
• Denervation of external intercostals reduced but did not eliminate their inspiratory shortening, which reversed to lengthening after subsequent parasternal denervation.

Conclusions:

• Both parasternal and external intercostal muscles act agonistically during inspiration in dogs.
• Parasternal muscles significantly influence external intercostal muscle length changes during resting breathing.
• Parasternal intercostals appear to play a more dominant role than external intercostals in elevating ribs during normal canine inspiration.