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Overnight monitoring of lung mechanics and Tidal expiratory flow limitation (EFLT) by Forced Oscillation Technique (FOT) in Chronic Obstructive Pulmonary Disease (COPD) receiving non-invasive ventilation (NIV): the impact of sleep and posture

Tidal expiratory flow limitation (EFLT) promotes Intrinsic PEEP (PEEPi) which has detrimental effects on respiratory mechanics. FOT can monitor EFLT by measuring within-breath changes in reactance at 5Hz (ΔXRS) (Dellaca et al ERJ 2004), a breath is considered as EFL if ΔXRS >2.8 cmH2Os/L. This technique has been incorporated in a prototype of NIV ventilator (Synchrony, Philips/Respironics, Pittsburgh, USA) and used to assess EFLT breath by breath over one night. Five COPD patients (FEV1%pred=39.4±13.5%; FEV1/FVC%pred=50.4±19.9%) on NIV were studied over one night while receiving their prescribed ventilatory settings. ΔXRS was assessed continuously and evaluated according to posture and sleep stages: awake, rapid eye movement (REM) and non-REM (NREM). Patients spent 81.3(31.4)% of the night in supine position, 18.7(31.4)% on the side, 6.6(31.2)% in REM, 70.6(38.1)% in NREM and 22.8(24.1)% awake (data reported as median(IQR)). The correspondent averaged values of ΔXRS, expressed in cmH2Os/L, are reported in the table:
 Supine posture in REM stages shows the highest ΔXRS and, on average, supine posture worsens EFL (ΔXRS 3.1(0.8) vs 1.8(0.3) cmH2Os/L). The value of ΔXRS is highly variable within the night and depends on both posture changes and sleep stages.