Positive- and Negative-Pressure Ventilation Characterized by Local and Global Pulmonary Mechanics

Area of Science:

• Pulmonary Mechanics
• Biomedical Engineering
• Respiratory Physiology

Background:

• Ongoing debate exists regarding the equivalency of positive-pressure ventilation (PPV) and negative-pressure ventilation (NPV).
• Understanding the differences is crucial due to distinct clinical applications and outcomes associated with each ventilation strategy.

Purpose of the Study:

• To investigate the mechanical parallels between PPV and NPV.
• To determine if PPV and NPV produce identical ventilation profiles by analyzing local strain mechanics under matched global tidal volume and inflation pressure.

Main Methods:

• Utilized a custom electromechanical apparatus to apply equal global loads and displacements to ex vivo porcine lungs using both PPV and NPV.
• Employed high-speed, high-resolution cameras to record real-time lung surface deformations and strains.
• Assessed differences in global energetics, viscoelasticity, and local tissue distortion between PPV and NPV.

Main Results:

• NPV demonstrated significantly greater bulk pressure-volume compliance during initial inflation, suggesting earlier lung recruitment.
• NPV settings resulted in reduced relaxation, hysteresis, and energy loss compared to PPV.
• Analysis of tissue anisotropy revealed decreased local strain trends and reduced tissue distortion with NPV.

Conclusions:

• Equivalent transpulmonary pressures in PPV and NPV yield identical lung volumes and pressures, but local tissue strains differ.
• These findings, despite ex vivo limitations, may reconcile contradictory previous studies.
• The observed differences in local tissue strain could explain reported benefits of NPV, such as improved oxygenation and reduced lung injury.