Non Invasive ventilation (NIV) in chronic ventilatory failure: A comparison of different modes of ventilation and an analysis of mechanisms of action

INTERVENTION: Pressure support ventilation vs volume cycled ventilation CONDITION: Nervous system diseases: Other nervous system disease ; Nervous System Diseases PRIMARY OUTCOME: Arterial blood gas tensions (pO2, PCO2) SECONDARY OUTCOME: 1. Exercise tolerance (shuttle walk tests) ; 2. Psychometric tests ; 3. Central respiratory drive (using ventilatory and PO.1 response to carbon dioxide) ; 4. Assessment of respiratory muscle strength (sniff nasal pressures). ; 5. Full polysomnography (sleep quality and efficiency) ; 6. Health status INCLUSION CRITERIA: Patients with established chronic respiratory failure due to chest wall deformity or neuromuscular weakness stable of home nocturnal non‐invasive ventilation.