Abdominal compliance, parasternal activation, and chest wall motion

Area of Science:

• Respiratory Physiology
• Biomechanics of Breathing

Background:

• Chest wall mechanics differ between upright and supine postures.
• Abdominal compliance (Cab) is a key factor influencing breathing mechanics.

Purpose of the Study:

• To investigate the role of abdominal compliance in posture-related changes in chest wall motion.
• To determine if respiratory muscle recruitment patterns differ between postures.

Main Methods:

• Measured abdominal compliance (Cab), rib cage (Vrc), and abdominal (Vab) displacement in normal subjects.
• Utilized an abdominal binder to incrementally decrease Cab in the supine position.
• Recorded parasternal muscle electrical activity (EMGps) during CO2 rebreathing in different postures.

Main Results:

• Decreasing Cab with an abdominal binder in the supine posture increased the ratio of rib cage to abdominal displacement, mimicking upright posture.
• Supine posture without binding showed reduced rib cage-abdominal coordination compared to upright.
• Respiratory muscle activity (EMGps) was similar at equivalent tidal volumes in supine (bound and unbound) and upright postures, suggesting no difference in recruitment patterns.

Conclusions:

• Differences in chest wall motion between upright and supine postures are primarily attributed to variations in abdominal compliance.
• Respiratory muscle recruitment patterns do not appear to be the main driver of posture-dependent breathing mechanics.
• Altered mechanical coupling between the diaphragm and rib cage likely explains the observed changes in chest wall motion.