Expiratory flow limitation and intrinsic positive end-expiratory pressure in obesity

Breathing at very low lung volumes might be affected by decreased expiratory airflow and air trapping. Our purpose was to detect expiratory flow limitation (EFL) and, as a consequence, intrinsic positive end-expiratory pressure (PEEPi) in grossly obese subjects (OS). Eight OS with a mean body mass index (BMI) of 44 ± 5 kg/m2and six age-matched normal-weight control subjects (CS) were studied in different body positions. Negative expiratory pressure (NEP) was used to determine EFL. In contrast to CS, EFL was found in two of eight OS in the upright position and in seven of eight OS in the supine position. Dynamic PEEPiand mean transdiaphragmatic pressure (mean Pdi) were measured in all six CS and in six of eight OS. In OS, PEEPiincreased from 0.14 ± 0.06 (SD) kPa in the upright position to 0.41 ± 0.11 kPa in the supine position (P< 0.05) and decreased to 0.20 ± 0.08 kPa in the right lateral position (P< 0.05, compared with supine), whereas, in CS, PEEPiwas significantly smaller (<0.05 kPa) in each position. In OS, mean Pdi in each position was significantly larger compared with CS. Mean Pdi increased from 1.02 ± 0.32 kPa in the upright position to 1.26 ± 0.17 kPa in the supine position (not significant) and decreased to 1.06 ± 0.26 kPa in the right lateral position (P< 0.05, compared with supine), whereas there were no significant changes in CS. We conclude that in OS1) tidal breathing can be affected by EFL and PEEPi;2) EFL and PEEPiare promoted by the supine posture; and 3) the increased diaphragmatic load in the supine position is, in part, related to PEEPi.