Effective respiratory system elastance during positive-pressure breathing in supine man

Area of Science:

• Respiratory Physiology
• Mechanical Ventilation
• Biomechanics

Background:

• Understanding respiratory system mechanics is crucial for optimizing mechanical ventilation.
• The interplay between positive end-expiratory pressure (PEEP) and respiratory system elastance requires further elucidation.

Purpose of the Study:

• To investigate the effects of varying positive end-expiratory pressures (PEEP) on the elastance of the respiratory system and its components.
• To quantify the contribution of the abdomen-diaphragm system to tidal volume during mechanical ventilation.

Main Methods:

• Healthy male subjects were mechanically ventilated on a ballistobed at PEEP levels from 0 to 19 cmH2O.
• Pressures (airway opening, esophageal, gastric) and tidal volume were monitored.
• Respiratory system (E'rs) and component elastances (E'ab, E'di, E'rc) were calculated.

Main Results:

• Lung compliance slightly increased with PEEP.
• Rib cage (E'rc) and diaphragm (E'di) elastances decreased linearly, while abdominal muscle (E'ab) elastance increased linearly.
• The combined elastance of the abdomen and diaphragm (E'ab+di) initially decreased then increased.
• The abdomen-diaphragm contribution to tidal volume was approximately half that during spontaneous breathing.

Conclusions:

• PEEP significantly influences the mechanical properties of the respiratory system, particularly the abdominal compartment.
• The mechanical load on the respiratory system changes with PEEP, affecting the balance between chest wall and abdominal contributions.
• Findings provide insights into respiratory mechanics during mechanical ventilation and may inform ventilator management strategies.