Physiological effects of bi-level high-flow nasal cannula in healthy individuals: a proof of concept trial

Abstract

Background: High-flow nasal cannula (HFNC) delivers a continuous, unidirectional high flow of oxygen (Uniflow) throughout the respiratory cycle. Despite its positive pressure effects in the nasopharynx, the persistent high flow during expiration imposes additional work of breathing and disrupts the patient's neural respiratory cycle. We devised a bi-level high-flow system (Biflow) allowing separate flow rate adjustments for inspiration and expiration.

Methods: We conducted a randomized crossover pilot study which we included healthy volunteer at ASAN Medical Center (April 2021 to June 2021). The data of 12 healthy volunteers (7 male, 5 female, average age 46.3 years) were analyzed. For Uniflow, flow settings of 30 (U30), 40 (U40), and 50 (U50) L/min were tested. In the Biflow, inspiratory flow rates were matched to the Uniflow settings, while expiratory flow rates varied from 10 to 30 L/min. The sequence of each flow (Uniflow vs. Biflow) was randomized and each flow setting was maintained for 3 min. Physiologic parameters, nasopharyngeal pressure-time product (N-PTP) as an energy cost proxy, end-expiratory lung impedance (EELI), and participant comfort were assessed.

Results: Uniflow decreased respiratory rate and elongated expiratory time compared to natural breathing. However, these effects were less pronounced during Biflow. Compared with the Uniflow, both expiratory and inspiratory N-PTP were lower during the Biflow. Transcutaneous CO₂ was lower during the Biflow compared with natural breathing or Uniflow. EELI did not differ between modes. All participants completed the study protocol without side effects.

Conclusion: In healthy participants, compared with the conventional HFNC (Uniflow), Biflow showed less interference with the natural respiratory cycle of the participants. Compared with Uniflow, energy cost occurring in the nasopharynx was lower during Biflow.

Clinical trial registration: http://cris.nih.go.kr/cris/, identifier KCT0006100.

Keywords: Biflow; concept trial; high flow nasal cannula; pressure-time product; respiratory cycle.

FIGURE 1

Consort flow diagram.

FIGURE 2

Airway pressure tracing (upper) and Bi-flow operating signal (lower). During Biflow, breath a was a failed operation, and breaths b and c were successful.

FIGURE 3

Changes in expiratory time and N-PTP (a) Change of expiration time of Biflow compared to Uniflow (b) Change of inspiratory PTP of Biflow compared to Uniflow (c) Change of expiratory PTP of Biflow compared to Uniflow (d) Change of total PTP of Biflow compared to Uniflow P-value of <0.05 compared with Uniflow, *P-value of <0.05 between Biflow settings. PTPinsp, inspiratory nasal pressure time product; PTPexp, expiratory nasal pressure time product; PTPtotal, total nasal pressure time product; U, Uniflow; B, Biflow.

FIGURE 4

Changes in TIV, GI index, EELI, and V/D ratio of EELI (a) Comparison of TIV among natural breathing, Uniflow and Biflow settings (b) Comparison of GI Index among natural breathing, Uniflow and Biflow settings (c) Comparison of EELI among natural breathing, Uniflow and Biflow settings (d) Comparison of V/D ratio among natural breathing, Uniflow and Biflow settings P-value of <0.05 compared with natural breathing, *P-value of <0.05 between Biflow settings. TIV, tidal impedance variation; GI, global inhomogeneity; EELI, end-expiratory lung impedance; V/D ratio, ventral/dorsal ratio; U, Uniflow; B, Biflow.