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Figure 6 Time course of the effect of postural changes on the response to negative expiratory pressure (NEP). Four left panels, in a representative patient (#2); two right panels, in a control subject. In the patient when first studied seated, flow limitation (FL) encompasses less than 50% of tidal volume (pFL; top panel, left). Flow limitation worsens (more than 50% of tidal volume, cFL) in supine position (top panel, right) and diminishes when the patient returns to the sitting position (bottom panels). The degree of FL continues to decrease for several minutes after resuming the sitting position, and after 15 min, the patient is no longer flow limited. In the control subject, there is no FL.