INFLUENCE OF NASAL OBSTRUCTION ON AUTO-CPAP BEHAVIOR DURING SLEEP IN SLEEP APNOEA HYPOPNOEA SYNDROME/

Background-Auto-CPAP machines have been developed to adapt automatical ly the positive pressure level to the required needs. The auto-CPAP re sponse to transient nasal obstruction was tested during sleep in patie nts with sleep apnoea/hypopnoea syndrome (SAHS). Methods-Nasal obstruc tion was induced by local instillation of histamine. Fourteen nasal ch allenges were performed on eight patients, seven while the patients we re on the ''Morphee plus'' apparatus and the other seven with the pati ents on the ''Horizon'' machine. Results-Nasal resistance increased in itially by a mean (SD) of 166 (66)% during the trials with the ''Morph ee plus'' and by 118 (44)% with the ''Horizon'' machine. The increase in nasal resistance was always accompanied by flow limitation with one exception. Mask pressure initially decreased to the minimal permitted value as nasal resistance increased with the ''Morphee plus'' device. A late increase of the positive pressure level occurred sometimes. Ma sk pressure did not change with increasing nasal resistance when the ' 'Horizon'' device was used. Conclusion-Neither the ''Morphee plus'' no r the ''Horizon'' device abolished flow limited breaths and resulting sleep fragmentation. We conclude that, despite the different algorithm of pressure changes, these auto-CPAP machines do not adequately respo nd to an acute increase in nasal resistance.