Detection of flow limitation during tidal breathing by the interruptor technique

In patients with airflow obstruction, flow limitation can be established in various ways. Using body plethysmography, flow limitation is assumed when expiratory flow decreases whilst alveolar pressure increases at the same time. During forced expiration, flow limitation can be established by means of the flow interruptor technique; flow limitation is assumed when, after release of an occlusion, a spike flow superimposed on the ongoing alveolar flow (delta peak flow) is detected. In this study, the flow interruptor technique was applied to detect flow limitation during tidal breathing. The results were compared to those obtained with the body plethysmograph. The expiratory flow pattern, post-interruption, was analysed in 33 subjects; 11 patients with airflow obstruction and flow limitation established with the body plethysmograph (AO+); 11 patients with airflow obstruction without flow limitation (AO-); and 11 healthy volunteers. Mean spike areas were 27.6 +/- 18.3, 4.6 +/- 2.3 and 3.4 +/- 2.0 mL for the AO+, AO- and control group, respectively, showing a highly significant difference between the AO+ patients and the other groups. Also, significantly higher delta peak flows were found in the AO+ patients compared to the other groups. No differences in delta peak flows or spike areas could be established between patients without flow limitation and controls. We conclude that the interruptor technique may be a useful means of assessing flow limitation during tidal breathing.