We have assessed a new method, manual compression of the abdominal wall (MCA) during expiration, in the detection of expiratory flow limitation. Twelve stable patients with chronic obstructive pulmonary disease (COPD) and five normal subjects were studied during spontaneous breathing in the supine and seated posture. MCA was performed during expiration with one hand at the umbilical level and we measured flow, volume, pleural (Ppl) and gastric (Pga) pressures and abdominal anteroposterior (AP) diameter at the umbilical level with magnetometers. No increase in expiratory flow during MCA relative to the preceding breath despite associated increases in pressures was considered as indicating expiratory flow limitation. In seven additional patients with increased upper airway collapsibility (obstructive sleep apnea syndrome [OSAS]), MCA was compared with negative expiratory pressure (NEP). In normal seated subjects, MCA was associated with a decrease in abdominal AP dimension (mean +/- SD: -27 +/- 6%), an increase in Pga (14.7 +/- 7.4 cm H(2)O) and Ppl (6.2 +/- 2.2 cm H(2)O), and an increase in expiratory flow. MCA caused similar changes in abdominal AP dimension and pressures in seated patients with COPD but six of them (50%), including four patients with FEV(1) less than 1 L, had no increase in expiratory flow. In the supine posture, MCA always increased expiratory flow in normal subjects but four additional patients with COPD showed evidence of flow limitation. MCA invariably increased expiratory flow in patients with OSAS whereas the NEP method suggested flow limitation in some cases. We conclude that MCA is a very simple method that allows detection of flow limitation in different positions.