What question did this study set out to answer?

This research aims to determine how different flow settings of high-flow nasal cannula (HFNC) impact lung impedance in healthy adults.

March 26, 2026

629: Effect of Flow Settings on Lung Impedance: A Randomized Crossover Study in Healthy Subjects

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This research aims to determine how different flow settings of high-flow nasal cannula (HFNC) impact lung impedance in healthy adults.
Randomized crossover trial design
Enrolled healthy adults for HFNC at 20, 40, and 60 L/min flows
Measured end-expiratory lung impedance (EELI) using Electrical Impedance Tomography (EIT)
Monitored tidal volume and respiratory rate before each flow setting
Included additional testing with Bi-flow settings (20-20 and 20-40 L/min).
EELI increased significantly at 40 L/min (74±16 units) and 60 L/min (131±20 units), but not at 20 L/min (p=0.551).
Flow at 60 L/min resulted in a higher EELI compared to 20 and 40 L/min (p=0.002 and p<0.001).
HFNC reduced respiratory rate by 2±0.6, 4±1, and 5±0.8 breaths/min at 20, 40, and 60 L/min, respectively (p<0.001).
Only the 60 L/min flow increased tidal volume variation (22±5 units, p=0.001)
Both Bi-flow settings increased EELI compared to baseline but did not significantly alter tidal volume variation.

Resumen

Introduction: High-flow nasal cannula (HFNC) oxygen therapy reduces work of breathing and improves oxygenation by providing flows that meet a patient’s peak inspiratory flow during tidal breathing. Despite its widespread use, the optimal flow setting remains unclear. Studies suggest a positive correlation between HFNC flows and end-expiratory lung impedance (EELI), the findings have been inconsistent. This study evaluated the effect of various flows on EELI using a novel HFNC system (HFT 750, MEKICS Ltd) and Electrical Impedance Tomography (EIT) device in healthy adults. Methods: Upon approval from ethic committee (No.23101708-IRB01), this randomized crossover trial enrolled healthy adults to receive HFNC at different flow settings (20, 40, and 60 L/min) in a random order. Some participants also received additional testing with two Bi-flow settings (20-20 and 20-40 L/min). Each setting was used for 20 minutes, followed by a 5-minute wash out period during which HFNC was removed. Before each flow, tidal volume and respiratory rate (RR) were obtained by a respiratory monitor. Throughout the study periods, EELI and tidal volume variation were monitored using EIT. Results: 26 subjects were enrolled between May and October 2024. All completed the standard flow interventions, and 12 also underwent Bi-flow. Compared to baseline, EELI significantly increased at 40 and 60 L/min, with increments of 74±16 and 131±20 units, respectively (both p0.05). Conclusions: In healthy volunteers, HFNC significantly increased EELI only at flow of 40 L/min or higher. RR decreased with increasing flows, but tidal volume variation increased only at 60 L/min. Both Bi-flow settings enhanced EELI without significantly altering tidal volume variation.

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