EXPIRATORY FLOW LIMITATION AND INTRINSIC POSITIVE END-EXPIRATORY PRESSURE IN OBESITY

Breathing at very low lung volumes might be affected by decreased expi ratory airflow and air trapping. Our purpose was to detect expiratory flow limitation (EFL) and, as a consequence, intrinsic positive end-ex piratory pressure (PEEPi) in grossly obese subjects (OS). Eight OS wit h a mean body mass index (BMI) of 44 +/- 5 kg/m(2) and six age-matched normal-weight control subjects (CS) were studied in different body po sitions. Negative expiratory pressure (NEP) was used to determine En. In contrast to CS, EFL was found in two of eight OS in the upright pos ition and in seven of eight OS in the supine position. Dynamic PEEPi a nd mean transdiaphragmatic pressure (mean Pdi) were measured in all si x CS and in six of eight OS. In OS, PEEPi increased from 0.14 +/- 0.06 (SD) kPa in the upright position to 0.41 +/- 0.11 kPa in the supine p osition (P < 0.05) and decreased to 0.20 +/- 0.08 kPa in the right lat eral position (P < 0.05, compared with supine), whereas, in CS, PEEPi was significantly smaller (<0.05 kPa) in each position. In OS, mean Pd i 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 1.0 6 +/- 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 OS 1) tidal breathing can be affected by EFL and PEEPi; 2) EFL and PEEPi are promoted by the supine posture; and 3) the increased di aphragmatic load in the supine position is, in part, related to PEEPi.