Comparison between plethysmographic and forced oscillation techniques in the assessment of airflow obstruction.

We compared airway resistances (Raw, body plethysmograph) and total pulmonary resistance at 4 and 24 Hz (RRS 4 Hz, 24 Hz) as well as the resonant frequency (RF), both in normals and in patients with airway obstruction. Bronchodilatation (n = 38) was the best evaluated by the induced changes in RRS 4 Hz and RF. However, the importance of change of RRS 4 Hz was poorly correlated with the change in Raw. Bronchial challenge test with histamine and DPT was again the best evaluated by RRS 4 Hz and RF with maximal changes observed for the latter. Normal ranges for Raw, RRS 4 Hz and RF were computed (n = 41). For all patients studied (n = 42) concordance for abnormality was good but poor for normality. From this we conclude that the oscillation technique is a different approach for the evaluation of airway obstruction and that RRS 4 Hz or RF are easy and accurate measurements to follow during bronchodilatation and bronchoconstriction tests.