Unloading work of breathing during high-frequency oscillatory ventilation: a bench study

Area of Science:

• Mechanical Ventilation
• Respiratory Physiology

Background:

• High-frequency oscillatory ventilation (HFOV) can impose a significant work of breathing (WOB) on patients.
• Spontaneous breathing efforts during HFOV often necessitate suppression due to high imposed WOB.

Purpose of the Study:

• To design and evaluate a demand-flow system to reduce imposed WOB during HFOV.
• To assess the system's effectiveness in facilitating spontaneous breathing in patients.

Main Methods:

• An external gas flow controller (demand-flow system) was developed to manage fresh gas flow during spontaneous breathing simulations.
• A control algorithm was implemented to detect breathing effort and regulate the demand-flow valve.
• Bench testing using Campbell diagrams and pressure time product (PTP) quantified the imposed workload.

Main Results:

• The demand-flow system reduced inspiratory imposed WOB by 30-56% and inspiratory PTP by 38-59%.
• Expiratory imposed WOB decreased by 12-49%.
• Fluctuations in mean airway pressure were markedly reduced, with maximum imposed WOB within the physiological range.

Conclusions:

• The demand-flow system effectively reduces imposed WOB and airway pressure fluctuations during HFOV.
• This reduction may enable easier maintenance of spontaneous breathing during HFOV.
• The system could facilitate earlier initiation of HFOV and potential weaning directly on the ventilator.