Adjustment of Mask Pressure, for Bilevel Positive Airways Pressure Therapy, by Automated Algorithm

Inclusion Criteria: * Subjects will be patients not naive to noninvasive ventilation, and being so treated for any form of hypercapnic ventilatory failure. * Previously stabilised on bilevel noninvasive pressure support ventilation. * Both genders, age \<75years. * Previously shown to have a requirement for an EEP above cm H2O in order to maintain upper airway patency, or those in whom such a raised EEP would be expected, e.g. obese patients. * Patients also known to have adequate airway patency at an EEP of 4 to 5 cm H2O will be included to ensure specificity of the algorithm. Exclusion Criteria: * Acute critical illness (e.g. acute coronary syndrome, stroke) * Serious anatomical variations of nose, sinuses, pharynx or oesophagus. * Any condition at risk of oesophageal bleeding (e.g. oesophageal varices, gastric ulcer, etc.) * Age \>75 years * Pregnancy * Epilepsy * Psychiatric disorders that could possibly influence the study * Any kind of addiction * Insufficient knowledge of the language * Noninvasive ventilation otherwise contraindicated