Evaluation of a test of density-dependence of the expiratory flows in the screening of peripheral airways obstruction.

A test of density-dependence of flow at 50% of vital capacity has been investigated in two groups of subjects (86 in total) in order to evaluate respectively: a) influences that on it may be exerted by altered mechanical properties of the lung in chronic airflow obstruction; b) accuracy and precision of the test in latent and clinical asthma. Lung elastic recoil pressure does not seem to be related to the intensity of density-dependence. Relationships between MEF50 on air and on He-O2, expressed as means of groups allow distinguish between each other, whereas a definite overlap between groups is patent; absolute flows, either on air or on He-O2 are quite satisfactorily reproducible, both in health and disease. Delta% MEF50 shows a good specificity but a poor sensitivity; reproducibility is unacceptable, unless when using on a qualitative scale of figure of 20% as borderline to distinguish subjects responders from non responders.