Mechanical advantage of the canine triangularis sterni

Area of Science:

• Respiratory Physiology
• Comparative Anatomy

Background:

• Previous research linked maximal changes in airway opening pressure per unit muscle mass (ΔPao/m) to fractional muscle length changes in canine inspiratory muscles.
• The triangularis sterni is a key expiratory muscle of the canine rib cage.

Purpose of the Study:

• To investigate the validity of the established relationship for the canine triangularis sterni, an expiratory muscle.
• To determine if a unique relationship exists between respiratory muscle length changes and ΔPao/m for both inspiratory and expiratory muscles.

Main Methods:

• Passive lung inflation to increase functional residual capacity (FRC) in dogs.
• Maximal electrical stimulation of the triangularis sterni muscle at different lung volumes.
• Measurement of changes in airway opening pressure (Pao) and muscle length.
• Geometric analysis of the canine rib cage structure.

Main Results:

• Passive inflation induced a nearly linear increase in triangularis sterni muscle length.
• The coefficient of proportionality between triangularis sterni length change during passive inflation and ΔPao/m was consistent with previous findings for inspiratory muscles.
• Canine triangularis sterni lengthening during passive inflation is significantly greater than parasternal intercostal shortening due to rib cage geometry.

Conclusions:

• A unique relationship exists between fractional changes in respiratory muscle length and ΔPao/m for both inspiratory and expiratory muscles.
• The maximal effect of a respiratory muscle on lung mechanics can be predicted using its passive length change and mass.
• Rib cage geometry in dogs influences the differential length changes of inspiratory and expiratory muscles.