CBF was measured by transcranial Doppler by mean of LMCAFV immediately before NIV, during NIV at 5, 30 and 60 minutes and after NIV removal at 5 and 30 minutes. ABG were collected immediately before the experiment, after one hour of NIV breathing and 30 minutes after NIV discontinuation. Respiratory rate (RR), tidal volume (VT), oxygen saturation by pulse oximetry (SpO2), heart rate (HR), minute ventilation (VE) and mean systemic arterial blood pressure (MAP) were continuously measured by a multiparameter monitor (Dixtal DX-2010™, Dixtal, Manaus, Brazil) both on spontaneous respiration and NIV.