[The utility of the flow-volume curve in detecting fixed extrathoracic stenoses in patients with chronic obstructive...

The flow-volume curve is the usual noninvasive diagnostic test for upper airways obstruction. In order to assess its usefulness for the detection of fixed upper airways obstruction in chronic obstructive pulmonary disease (COPD), we plotted flow-volume curves using maximum inspiratory and expiratory maneuvers in 60 COPD patients and in 15 healthy controls. Baseline readings were taken, followed by readings after random application of fixed external resistances with diameters of 4, 6, 8 and 10 mm in all cases. Although PEF and FIF50 decreased significantly with resistance of 10 mm, even in the group with the most severe ventilatory limitation it was necessary to reduce the internal diameter to 6 mm to detect changes in FEV1. In patients with baseline values under 50% of theoretical values, 4 mm stenosis was required to provoke changes in FEV1. The fall in FEV1 and PEF was less evident as the severity of COPD increased, with both parameters correlating with percent baseline FEV1 only at diameters of 6 mm (p < 0.01) and 4 mm (p < 0.001). The sensitivities of the usual indices for detecting upper airways obstruction, such as FEV1/PEF and FEV1/FEV0-5, were low (below 50%) in all groups at diameters over 6 mm, and in the most severe cases of COPD, even with stenosis of 4 mm. Nor did other indices, such as FEF50/FIF50 and FEV1/FIV1,, give better diagnostic yield. We conclude that the flow-volume curve may not detect the existence of upper airways obstruction in COPD, and that in the most severely affected patients alternative diagnostic methods should therefore be considered.