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

Breathing at very low lung volumes might beaffected by decreased expiratory airflow and air trapping. Our purposewas to detect expiratory flow limitation (EFL) and, as a consequence, intrinsic positive end-expiratory pressure(PEEP_i) in grossly obesesubjects (OS). Eight OS with a mean body mass index (BMI) of 44 ± 5 kg/m² and six age-matchednormal-weight control subjects (CS) were studied in different bodypositions. Negative expiratory pressure (NEP) was used to determineEFL. In contrast to CS, EFL was found in two of eight OS in the uprightposition and in seven of eight OS in the supine position. DynamicPEEP_i and mean transdiaphragmatic pressure (mean Pdi) were measured in all six CS and in six of eight OS.In OS, PEEP_i increased from 0.14 ± 0.06 (SD) kPa in the upright position to 0.41 ± 0.11 kPa inthe supine position (P < 0.05) anddecreased to 0.20 ± 0.08 kPa in the right lateral position(P < 0.05, compared with supine),whereas, in CS, PEEP_i wassignificantly smaller (<0.05 kPa) in each position. In OS, mean Pdiin each position was significantly larger compared with CS. Mean Pdiincreased from 1.02 ± 0.32 kPa in the upright position to 1.26 ± 0.17 kPa in the supine position (not significant) and decreasedto 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 affectedby EFL and PEEP_i;2) EFL andPEEP_i are promoted by the supineposture; and 3) the increaseddiaphragmatic load in the supine position is, in part, related toPEEP_i.