This study evaluates the work of breathing among healthy subjects under various conditions of treatment with high flow nasal cannulas. Ten subjects will be included. The design of this study is a cross over of five treatment periods with different flow settings.

High flow oxygen therapy (HFOT) is a promising technique increasingly used in the management of acute respiratory failure. In hospitalised hypoxemic patients, recent clinical evidence showed that HFOT can reduce endotracheal intubation and reduce mortality. Physiologically, the HFOT causes a decrease in respiratory rate and minute-ventilation and may be associated with a decrease in carbone dioxyde arterial pressure. It is possible that these effects are associated with decreased work of breathing, which could explain some of the benefits in terms of comfort and efficiency.

The objective of this research is to evaluate the impact of a wash-out of anatomical dead space by high flow nasal cannulas on respiratory parameters and on the work of breathing among healthy subjects. The investigators will evaluate the baseline status in room air, and then compare it with four different levels of flow. The primary endpoint will be the work of breathing.

Inclusion Criteria:

• Healthy subjects
• Written and informed consent

Exclusion Criteria:

• Pregnant or breastfeeding women;
• Subject enrolled in another study excluding co-enrolment;
• Cardio-vascular or respiratory disease;
• History of ear nose and throat disease (i.e. surgery, epistaxis, trauma), eso-gastric disease (i.e. esophageal varices, digestive haemorrhage), rheumatologic or neurologic disease possibly interfering with the design of the study;
• Subject feeling nauseous or under recent fed condition (<1h).