Furthermore the secondary aim is to observe any relationship between diaphragmatic function (excursion), diaphragmatic thickening and the timing of arterial blood gases (ABGs) compensation in patients with AECOPD undergoing NIV treatment; additional outcomes are: correlation with dyspnea level, time of mechanical ventilation, NIV failure, rate of tracheostomy, length of stay in ICU and in-hospital and 90-day mortality.