Table 1.
Gas composition, pressure in the hypopharynx, and respiratory parameters at different preset flows, 100% inspiratory fraction of oxygen, and various breathing patterns of volunteers
| Variable | Breathing Pattern (BP) | HFNC flow rate | P between preset flow | ||
|---|---|---|---|---|---|
| 30 L/min | 60 L/min | 80 L/min | |||
| FiO2, % | CM | 98.3 (95.3–99.6) | 99.9 (98.2–100.0)* | 100.0 (99.3–100.0)** | < 0.001 |
| OM | 84.8 (41.7–94.0)† | 91.2 (35.6–100.0)*† | 97.8 (39.4–100.0)**† | 0.021 | |
| HCM | 81.4 (77.2–94.3) ‡ | 96.9 (94.1–99.8)* | 99.0 (98.1–100.0)** | < 0.001 | |
| HOM | 59.2 (32.8–67.2)# | 66.6 (34.1–85.9)# | 64.3 (36.3–82.3)**# | 0.014 | |
| p between all BP | < 0.001 | < 0.001 | < 0.001 | ||
| Abnormal oxygram waveform, n (%) | CM | 0 | 0 | 0 | NA |
| OM | 7 (35)† | 11 (55)† | 11 (55)† | 0.069 | |
| HCM | 13 (65) ‡ | 15 (75) ‡ | 16 (80) ‡ | 0.247 | |
| HOM | 15 (75) | 17 (85) | 17 (85) | 0.135 | |
| p between all BP | < 0.001 | < 0.001 | < 0.001 | ||
| FeCO2, % | CM | 2.9 (2.6–3.6) | 2.6 (2.1–3.4)* | 2.1 (1.8–3.1)** | < 0.001 |
| OM | 2.6 (2.2–2.9)† | 2.2 (1.6–2.9)*† | 2.0 (1.7–2.4)** | 0.001 | |
| HCM | 2.4 (2.2–3.2) ‡ | 2.0 (1.6–2.6)*‡ | 1.7 (1.4–2.5) **‡ | < 0.001 | |
| HOM | 1.9 (1.7–2.2)# | 1.8 (1.5–2.3)* | 1.4 (1.1–1.7)**§# | < 0.001 | |
| p between all BP | < 0.001 | < 0.001 | < 0.001 | ||
| Expiratory pressure, cmH2O | CM | 3.8 (3.1–6.6) | 7.6 (6.4–11.4)* | 11.1 (7.7–14.8)** § | < 0.001 |
| OM | 1.2 (0.7–1.4)† | 1.5 (0.9–2.3)† | 1.5 (0.8–2.9)† | 0.102 | |
| HCM | 5.8 (3.5–8.2) ‡ | 9.4 (6.8–13.1)* ‡ | 12.7 (8.2–18.1)** § ‡ | < 0.001 | |
| HOM | 1.5 (1.1–1.7)# | 2.4 (1.4–2.7)*# | 3.0 (1.3–3.8)**# | 0.005 | |
| p between all BP | < 0.001 | < 0.001 | < 0.001 | ||
| Delta pressure, cmH2O | CM | 3.5 (2.5–5.8) | 3.5 (1.9–9.4) | 4.5 (1.4–11.4) | 0.500 |
| OM | 1.1 (0.8–1.5)† | 1.2 (0.7–1.7)† | 1.5 (0.6–3.7)† | 0.584 | |
| HCM | 7.1 (4.5–10.0) ‡ | 9.9 (6.1–14.7) ‡ | 12.2 (9.1–18.6) **‡ | 0.009 | |
| HOM | 1.8 (1.3–3.2)# | 2.1 (1.6–3.7)# | 1.9 (1.1–4.4)# | 0.383 | |
| p between all BP | < 0.001 | < 0.001 | < 0.001 | ||
| Minimal inspiratory pressure, cmH2O | CM | 0.5 (0.3–1.5) | 3.9 (2.3–5.1)* | 5.4 (1.5–8.0)** | 0.001 |
| OM | 0.3 (0.0–0.4) | 0.3 (0.0–0.9)† | 0.2 (−0.2–1.0)† | 0.212 | |
| HCM | −1.9 (−3.9–0.3) ‡ | 0.6 (−2.5–2.5)*‡ | 0.5 (−2.4–2.7)**‡ | 0.025 | |
| HOM | −0.5 (−1.8–0.3) | −0.1 (−1.3–0.5) | 0.0 (−0.7–0.5) | 0.097 | |
| p between all BP | < 0.001 | < 0.001 | < 0.001 | ||
| Exhaled tidal volume, mL | CM | 711.0 (608.3–790.0) | 948.0 (715.0–1204.8)* | 948.0 (869.0–1422.0)** | < 0.001 |
| HCM | 790.0 (681.4–898.6) | 987.5 (869.0–1194.9)* | 1027.0 (869.0–1264.0)** | < 0.001 | |
| p between BP | 0.059 | 0.808 | 0.819 | ||
| Respiratory rate, min−1 | CM | 11.0 (9.3–16.0) | 10.5 (8.0–14.0) | 10.0 (7.0–15.0)** | 0.043 |
| OM | 14.0 (11.0–16.8) | 15.0 (12.0–18.9) | 16.0 (12.0–19.0) | 0.531 | |
| HCM | 27.0 (24.3–30.0) ‡ | 30.0 (28.0–32.8)* ‡ | 30.0 (28.0–33.0)** ‡ | 0.004 | |
| HOM | 30.0 (28.0–31.0) # | 31.0 (30.0–33.0)* | 32.0 (29.0–35.0)** | 0.006 | |
| p between BP | < 0.001 | < 0.001 | < 0.001 | ||
| Ventilatory ratio (modified), AU | CM | 0.62 (0.49–0.91) | 0.59 (0.38–0.88) | 0.50 (0.40–0.73) | 0.076 |
| HCM | 1.13 (0.54–1.54) ‡ | 1.22 (0.96–1.50) ‡ | 1.05 (0.71–1.84) ‡ | 0.949 | |
| p between BP | < 0.001 | < 0.001 | < 0.001 | ||
| Expiratory time, s | CM | 3.4 (2.2–5.4) | 3.4 (2.9–6.0) | 3.7 (2.5–5.8) | 0.759 |
| HCM | 1.2 (1.0–1.3) ‡ | 1.0 (0.9–1.2) ‡ | 1.0 (0.9–1.2) ‡ | 0.063 | |
| p between all BP | < 0.001 | < 0.001 | < 0.001 | ||
| Inspiratory time, s | CM | 1.7 (1.2–2.0) | 1.7 (1.1–2.0) | 1.8 (1.2–1.9) | 0.570 |
| HCM | 1.0 (1.0–1.2) ‡ | 0.9 (0.8–1.0) *‡ | 0.9 (0.8–1.0)**‡ | 0.002 | |
| p between all BP | < 0.001 | < 0.001 | < 0.001 | ||
| Ti/Te, ratio | CM | 0.47 (0.30–0.65) | 0.41 (0.34–0.50) | 0.49 (0.29–0.60) | 0.311 |
| HCM | 0.90 (0.77–1.00) ‡ | 0.91 (0.83–1.00) ‡ | 0.83 (0.76–1.00) ‡ | 0.156 | |
| p between all BP | 0.001 | < 0.001 | 0.001 | ||
| Visual-analog scale of comfort, points | CM | 8.0 (7.3–9.8) | 7.0 (5.3–8.8)* | 6.0 (4.0–8.0)** § | < 0.001 |
| OM | 8.0 (7.0–9.8) | 6.5 (5.3–8.8)* | 6.0 (3.0–8.0)** § | < 0.001 | |
| HCM | 8.0 (6.3–9.0) | 6.5 (5.0–8.0)* | 6.0 (3.0–8.0)** | < 0.001 | |
| HOM | 8.0 (6.3–9.0) | 6.5 (5.0–8.0)* | 5.5 (3.0–8.0)** | < 0.001 | |
| p between all BP | 0.030 | 0.051 | 0.866 | ||
| Mean inspiratory flow, L/min | CM | 26.3 (20.3–33.6) | 39.6 (27.1–49.8)* | 44.8 (30.1–51.8)** | 0.003 |
| HCM | 43.6 (40.3–52.1) ‡ | 61.6 (50.0–77.0)* ‡ | 68.4 (56.9–90.9)** ‡ | < 0.001 | |
| p between all BP | < 0.001 | 0.001 | 0.001 | ||
| Preset flow/mean inspiratory flow | CM | 1.14 (0.89–1.48) | 1.51 (1.20–2.21) | 1.79 (1.54–2.66)** § | 0.001 |
| HCM | 0.69 (0.58–0.74) ‡ | 0.97 (0.78–1.20)* ‡ | 1.17 (0.88–1.41)** ‡ | < 0.001 | |
| p between all BP | < 0.001 | 0.001 | 0.001 | ||
Data are presented as median (interquartile range)
HFNC high flow oxygen through nasal cannula, BP breathing pattern, CM quiet breathing with closed mouth, OM quiet breathing with opened mouth, HCM hyperpnea with closed mouth, HOM hyperpnea with opened mouth, FiO2 measured inspiratory oxygen fraction, FeO2 measured expiratory oxygen fraction, FeCO2 end-expiratory carbon dioxide fraction, AU arbitrary units, VAS visual-analog scale (10 points—maximal comfort, 1 point—maximal discomfort), Te expiratory time, Ti inspiratory time
Significant differences (Friedman test with Bonferroni correction for multiple comparisons or Cochran’s Q test, where appropriate with p < 0.05) between preset flows with stable respiratory pattern: * 30 vs 60 l/min, ** 30 vs 80 l/min, § 60 vs 80 l/min. Significant differences (Friedman test with Bonferroni correction for multiple comparisons or Cochran’s Q test, where appropriate with p < 0.05) between different respiratory patterns with a constant preset flow: †CM vs OM, ‡CM vs HCM, #HCM vs HOM
Significant differences in p values are highlighted in bold