Changes in rib cage shape during quiet breathing, hyperventilation and single inspirations.

Area of Science:

• Physiology
• Respiratory Mechanics
• Biomechanics

Background:

• Rib cage volume changes are crucial for breathing mechanics.
• Understanding rib cage shape dynamics during different breathing patterns is essential for respiratory physiology.

Purpose of the Study:

• To investigate the relative changes in upper and lower rib cage volumes during various breathing conditions.
• To compare rib cage shape changes during relaxed breathing, quiet breathing, rapid breathing, exercise-induced hyperventilation, and single fast inspirations.

Main Methods:

• Utilized an induction coil plethysmograph (Respitrace) to measure rib cage volume changes (delta RCU and delta RCL).
• Studied seven normal seated subjects under controlled breathing conditions.
• Analyzed the relationship between upper and lower rib cage volume changes.

Main Results:

• Rib cage shape changes were similar during quiet breathing, rapid breathing, and exercise-induced hyperventilation compared to relaxed passive expiration.
• Single rapid inspirations exhibited marked and variable changes in rib cage shape, particularly early in inspiration.
• The plot of upper versus lower rib cage volume changes showed slight curvilinearity during relaxation.

Conclusions:

• Coordinated respiratory muscle activity during cyclic breathing results in a consistent pattern of rib cage shape change, mirroring relaxation.
• Distinct patterns of inspiratory muscle recruitment during single rapid inspirations lead to significantly different and variable rib cage shape dynamics.
• Findings support the concept that regional ventilation distribution is flow-independent during tidal breathing.