Some criteria for laminar conditions during HFV

Area of Science:

• Physiology
• Mechanical Ventilation
• Fluid Dynamics

Background:

• Assessing airflow regimes (laminar, transitional, turbulent) in the central airways during high-frequency ventilation (HFV) is crucial for understanding gas transport mechanisms.
• Existing empirical relationships can identify transitions from laminar to turbulent flow in tubes.

Purpose of the Study:

• To derive limiting relationships between dimensionless stroke volume and Womersley number for maintaining laminar flow conditions during HFV.
• To evaluate these relationships using lung models for humans and dogs.

Main Methods:

• Utilized published empirical relationships for flow regime identification in tubes.
• Derived limiting relationships for laminar flow maintenance based on dimensionless stroke volume and Womersley number.
• Applied these relationships to morphometric lung models of humans and dogs.

Main Results:

• Predicted maximum stroke volumes for humans and dogs using HFV agreed within 20% of experimentally reported values.
• Identified stroke volume-frequency combinations associated with declines in PaO2 and alveolar ventilation corresponded to nonlaminar flow conditions.

Conclusions:

• The derived limiting relationships effectively predict flow regimes during HFV in different species.
• This approach can guide the selection of HFV parameters (stroke volume, frequency) to achieve desired flow regimes.
• The method offers a valuable tool for analyzing HFV data and optimizing ventilation strategies.