On-line lung volume measurement during high-frequency oscillatory ventilation

Area of Science:

• Respiratory Physiology
• Critical Care Medicine
• Medical Instrumentation

Background:

• Functional residual capacity (FRC) is crucial for assessing lung function during mechanical ventilation.
• Existing methods for measuring lung volume may require interrupting ventilation, posing risks.
• High-frequency oscillatory ventilation (HFOV) presents unique challenges for continuous lung volume monitoring.

Purpose of the Study:

• To evaluate a bag-in-box system with helium dilution for measuring mean lung volume during HFOV.
• To assess the accuracy and reliability of this technique in lung models and animal subjects.
• To determine if the system can provide continuous lung volume data without interrupting HFOV.

Main Methods:

• A closed-circuit helium-dilution technique was implemented using a bag-in-box system.
• The system was tested on mechanical lung models and ten New Zealand adult rabbits (healthy and ALI groups).
• Helium rebreathing time for equilibration and volume accuracy were measured and compared to known volumes.

Main Results:

• The bag-in-box system demonstrated good correlation between measured and known lung volumes in models (p <.001).
• Helium equilibration times were approximately 50 seconds in models, 40-50 seconds in healthy rabbits, and 30-40 seconds in rabbits with acute lung injury (ALI).
• The method showed low coefficients of variation (0.5%-6.5%) for mean lung volume determinations in rabbits.

Conclusions:

• The bag-in-box helium-dilution technique is a viable method for measuring gas-containing lung volumes (10-60 mL).
• This approach can be used in patients undergoing high-frequency oscillatory ventilation.
• The system offers potential for non-interruptive lung volume monitoring in critical care settings.