Respiratory changes in parasternal intercostal intramuscular pressure

Area of Science:

• Respiratory Physiology
• Muscle Mechanics
• Biomechanics

Background:

• The parasternal intercostal muscles are crucial for breathing, but the forces they generate are not fully understood.
• Measuring parasternal intramuscular pressure (PIP) offers insight into the forces developed by these muscles.

Purpose of the Study:

• To investigate the forces exerted by parasternal intercostal muscles during various respiratory maneuvers.
• To correlate parasternal intramuscular pressure (PIP) with muscle activity and respiratory mechanics.

Main Methods:

• Measurements of parasternal intramuscular pressure (PIP) were taken in 14 supine anesthetized dogs using a microtransducer.
• Experiments included bilateral parasternal stimulation, quiet inspiration, inspiratory loading, airway occlusion, phrenicotomy, vagotomy, passive deflation, and passive inflation.

Main Results:

• A linear relationship was found between parasternal stimulation force and PIP (r > 0.95).
• Substantial PIP was generated during quiet inspiration (55 +/- 11.5 cmH2O).
• PIP increased proportionally with inspiratory resistive loading and airway occlusion (r = 0.82).
• Phrenicotomy and vagotomy increased inspiratory PIP rise by 21% and 99%, respectively.
• Large PIP rises (320 +/- 221 cmH2O) occurred during passive deflation, while it remained constant/decreased during passive inflation.

Conclusions:

• Parasternal intramuscular pressure (PIP) directly reflects the forces generated by parasternal intercostal muscles.
• These muscles exert significant forces on the ribs during both active and passive respiratory actions.
• PIP measurements provide a valuable tool for understanding the mechanical contribution of parasternal intercostals to breathing.