Effects of posture on tidal Expiratory Flow Limitation (EFLT) and on minimum PEEP(Positive End Expiratory Pressure) able to abolish it in Chronic Obstructive Pulmonary Disease (COPD) patients

Supine position may promote EFL T in COPD leading to intrinsic PEEP. The application of PEEP during NIV is used to counterbalance its effects. Forced oscillation technique (FOT) allows a real-time automatic optimization of PEEP (APEEP) by adjusting it continuously to abolish EFLT (Dellaca’ et al, ERJ 2004). The aim of this study is to evaluate the effect of posture on APEEP in COPD. 23 COPD patients (FEV 1 %pred= 40.1±16.6, FVC%pred=65.4±12.1 %) were studied seated (Se) first and then supine(Su) for 15 mins. PEEP was automatically adjusted continuously by a prototype of NIV ventilator (Synchrony, Philips, USA) incorporating FOT at 5Hz to abolish EFL T . APEEP, breathing pattern (tidal volume, V T , and minute ventilation, V E ) and inspiratory reactance (X RSi ) were recorded in the last 2 min of each condition. Data reported as median/IQR. When moving from the seated to the supine position APEEP, Vt, Ve and X RSi changed significantly (* p<0,05, tab.1) Data for patients never showing EFL T (NoEFL), withEFL T in both position (EFLSuSe) or only in the supine (EFLSu) are reported in tab.2 No differences of BMI and spirometry were found within groups. To abolish EFL T , PEEP must be increased in the supine position of an amount unpredictable from spirometry or anthropometric data.