Inspiratory Obstruction

Abstract

Obstructing lesions of the trachea and larynx which cause a predominantly inspiratory obstruction can be satisfactorily diagnosed by measuring both F.I.V.₁ and F.E.V.₁. Chronic airways obstruction involving intrathoracic airways produces a much lower F.E.V.₁/F.I.V.₁ percentage than normal, whereas obstruction to larynx and trachea causes a raised F.E.V.₁/F.I.V.₁ percentage. If flow-volume measurements are not available the F.E.V.₁/F.I.V.₁ percentage should provide a simple and useful method for diagnosis of upper airways obstruction.

In one of the patients reported a predominantly inspiratory obstruction caused CO₂ retention. In patients with airways obstruction the correlation between Pco₂ and F.I.V.₁ was found to be the same as between Pco₂ and F.E.V.₁. This suggests that respiratory failure can be caused by either inspiratory or expiratory airways obstruction and that neither is of greater importance in producing CO₂ retention.