Flow limitation during forced inspiration

In the case of a large obstructing lesion in the extrathoracic trachea or the larynx an inspiratory flow-limiting segment may develop outside the thorax. In such circumstances inspiratory flow does become effort independent (shown in the animation below).
The resulting inspiratory flow-volume curve is typical of the pathological problem, i.e. an inspiratory plateau at diminished flow. In the case of very severe obstruction expiratory flow may be similarly limited at a plateau in the absence of a compressed flow limiting segment.