Fig. 1. Schematic representation of the experimental setup. Negative or positive pressures could be rapidly applied to the nasal mask of the anesthetized subject. Pm= mask pressure; Pnp= nasopharyngeal pressure; Pop= oropharyngeal pressure; Php= hypopharyngeal pressure; Pes= esophageal pressure; Piso= isoflurane concentration; Pco2= carbon dioxide concentration; EMGgg = genioglossus electromyogram.