Inspiratory obstruction.

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 CO(2) retention. In patients with airways obstruction the correlation between Pco(2) and F.I.V.(1) was found to be the same as between Pco(2) 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 CO(2) retention.