Upper airway pressure distribution during nasal high-flow therapy

Area of Science:

• Respiratory physiology
• Biomedical engineering
• Fluid dynamics

Background:

• Nasal High-Flow Therapy (NHFT) utilizes two primary mechanisms: anatomical dead space washout and positive end-expiratory pressure (PEEP).
• Understanding the pressure distribution and jet penetration is crucial for optimizing NHFT efficacy.
• Direct in-vivo measurement of these parameters in patients is currently challenging.

Purpose of the Study:

• To investigate the respiratory pressure distribution and jet penetration length during NHFT.
• To determine the relationship between NHFT flow rate and PEEP in adult and infant upper airway models.
• To evaluate methods for predicting PEEP in different patient populations.

Main Methods:

• Utilized 3D-printed, anatomically correct upper airway models of an adult and an infant.
• Measured respiratory pressure distribution within the models under varying NHFT flow rates and cannula sizes.
• Assessed the correlation between flow rate, cannula size, jet penetration, and PEEP levels.

Main Results:

• NHFT jet penetration at end-expiration was observed to reach into or slightly beyond the nasal cavity, with minimal dependence on cannula size or flow rate.
• PEEP was found to be approximately proportional to the square of the flow rate, suggesting a 40% increase in flow rate can double PEEP.
• While PEEP was accurately predicted by prong-exit dynamic pressure in the adult model, this method proved unreliable in the infant model. Significant pressure fluctuations occurred with oversized cannulas relative to nostril size.

Conclusions:

• NHFT PEEP is significantly influenced by flow rate, with a quantifiable relationship observed in rigid airway models.
• Current methods for predicting NHFT-induced PEEP may not be universally applicable across different age groups, particularly in infants.
• Further research into patient-specific airway anatomy and aerodynamics is needed to refine NHFT parameter prediction and clinical application.