The aim of this study is to investigate the effects of setting airway pressure release valve (APL valve) on the anesthesia workstation to 5 cmH2O during spontaneous breathing on preoxygenation. In this prospective study healthy volunteers are randomized in cross-over between spontaneous breathing with the APL valve on spontaneous position or spontaneous breathing with the APL valve on 5 cmH2O or CPAP (continous positive airway pressure) mode with 5 cmH2O PEEP (positive end expiratory pressure).

There are several methods to improve preoxygenation but most of them require advanced anesthesia workstations. Therefore the investigators planned an an experimental study on healthy volunteers to investigate the effects of a simple method on preoxygenation.

Healthy volunteers are randomized in cross-over between spontaneous breathing with the APL valve on spontaneous position or spontaneous breathing with the APL valve on 5 cmH2O or CPAP mode with 5 cmH2O PEEP.

The volunteers will breath through an anesthesia face mask. The fresh gas flow rate is 12 L/min, inspiratory fraction of oxygen is 100%. The exhaled gas (oxygen and carbon dioxide) are monitored. The inspiratory and end expiratory fraction of oxygen will be recorded every 10 seconds.

The primary endpoint is the time to achieve end expiratory fraction of oxygen of 90% or more.The secondary endpoint is the proportion of subject with end expiratory fraction of oxygen of 90% or more after a 3 min period and the end expiratory fraction of oxygen at the third minute.

Inclusion Criteria:

• healthy volunteers

Exclusion Criteria:

• any respiratory disease