Figure 1From: Comparative evaluation of three interfaces for non-invasive ventilation: a randomized cross-over design physiologic study on healthy volunteersSchematic representation of the experimental design. (A) Spontaneous breathing; (B) face mask; (C) helmet standard; (D) helmet next. Pao, pressure at the airway opening; Pes, esophageal pressure; Pga, gastric pressure.Back to article page