**Abbreviations**

ALI: acute lung injury ApEn: approximate entropy AUC: area under the curve COPD: chronic obstructive pulmonary disease CPAP: continuous positive airway pressure CV: coefficient of variation ECG: electrocardiogram EEG: electroencephalogram FD: fractal dimension FFT: fast Fourier transformation FW: failure weaning HRV: heart rate variability ICU: intensive care unit LAA : low attenuation area LLE: largest lyapunov exponents LVEF: left ventricular ejection fraction MODS: multiple organ dysfunction syndrome MSE : multiscale entropy MV: minute ventilation PEEP: positive end-expiratory pressure PEF: peak expiratory flow PET: positron emission tomography

Pimax: maximal inspiratory pressure P0.1: airway occlusion pressure at 0.1 sec Pre-Botz: pre-Botzinger complex PSD: power spectrum density PSV: pressure support ventilation ROC: receiver operating characteristic RR: respiratory rate RSBI: rapid shallow breathing index SampEn: sample entropy SBT: spontaneous breathing trial SD: standard deviation SIMV: synchronized intermittent mandatory ventilation SIRS: systemic inflammatory response syndrome SW: successful weaning Te: expiratory time Ti: inspiratory time Ttot: total breath duration VT: tidal volume
