Figure 4.

Individual patient values and medians of the impedance-derived measures during high-flow nasal oxygen (HFNO), helmet continuous positive airway pressure (CPAP), and helmet noninvasive ventilation (NIV). Both helmet NIV and helmet CPAP increased the Vt compared with HFNO. Quasistatic respiratory system compliance was similar between HFNO and helmet NIV and showed a trend toward an increase during helmet CPAP. The application of positive end-expiratory pressure caused a significant increase in the end-expiratory lung impedance, which was related to recruitment in the dorsal lung regions, so the dynamic lung strain during helmet NIV and helmet CPAP decreased. Because of increased aeration of the dependent lung regions, both helmet NIV and helmet CPAP reduced the pendelluft effect.