The aim of the study is to compare the effect of two types of noninvasive ventilator (a small machine that assists breathing) in patients admitted to hospital with a sudden worsening of their existing breathing insufficiency, including an increase of carbon dioxide in the blood (hypercapnia) and acidity of the blood. Noninvasive ventilation (NIV) is standard therapy for patients with acute hypercapnic exacerbations (sudden worsening of existing breathing insufficiency) of both chronic obstructive pulmonary disease (COPD) and nonCOPD patients.