Table 2.

Effects on high-flow nasal cannula versus standard oxygen on respiratory variables

Variable	Standard oxygen	HFNC	p value
ΔPes, cmH2O	7.2 [5.6–10.3]	5.3 [4.2–7.1]	< 0.001
PTP, cmH2O. s	6.4 [5.3–8.9]	4.3 ± [3.4–6.2]	< 0.001
PTPmin, cmH2O. s/min	156 [114–238]	85 [67–140]	< 0.001
Pdi, cmH2O	7.3 [6.2–11.2]	5.9 [5.0–7.7]	0.008
Respiratory rate, bpm	24 ± 6	22 ± 5	0.001
VT Glob, ml	362 ± 112	334 ± 99	0.292
VT Dep, ml	261 ± 97	239 ± 76	0.206
VT Non-Dep, ml	101 ± 59	94 ± 60	0.554
VT, ml/kg IBW	6.2 ± 2.1	5.7 ± 1.9	0.482
Minute Ventilation, L/min	8.6 ± 2.8	7.4 ± 2.4	0.037
ΔEELVglob (change from standard oxygen), ml	0 [0–0]	169 [93–656]	< 0.001
Dynamic compliance, VT/ΔPes (ml/cmH20)	48 [33–62]	66 [40–82]	0.048
ΔEAdi, µV	14 [9–16]	10 [7–13]	0.022
Neuroventilatory efficiency, (VT/EAdi) ml/ µV	30 ± [24–36]	33 [22–54]	0.111
Diaphragmatic neuromuscular coupling, (Pdi/ΔEAdi) cmH2O/µV	0.65 [0.42–0.70]	0.61 [0.56–0.76]	0.256
A/P Ratio	0.41[0.25–0.62]	0.41 [0.16–0.59]	0.125
Center of ventilation	55 [52–58]	56 [50–60]	0.967
GI index	0.97 [0.87–1.38]	0.88 [0.75–1.5]	0.609
PaO2/FiO2, mmHg	240 ± 77	267 ± 80	0.012
PaCO2, mmHg	37 ± 4.7	37 ± 4.1	0.888
pH	7.45 ± 0.04	7.45 ± 0.05	0.898
Ventilatory ratio	1.36 ± 0.36	1.18 ± 0.39	0.035

Abbreviations: ΔPes: inspiratory esophageal pressure swing; PTP: pressure–time product per breath; PTP_min: pressure–time product per minute; Pdi: transdiaphragmatic pressure; V_{T Glob}: tidal volume global; V_{T Dep}: tidal volume dependent region; V_T-Nondep: tidal volume non-dependent region; ΔEELV_glob: variation of end expiratory lung volume; ΔEAdi: electrical activity of the diaphragm; A/P ratio: anterior to posterior ventilation ratio; GI index: global inhomogeneity index; PaCO₂: partial pressure of carbon dioxide. Normally distributed variables are expressed as the mean ± standard deviation; non-normal distributed variables are expressed as median and [interquartile range]. p values were calculated using a two-way repeated measures ANOVA