Tidal Expiratory Flow Limitation and NEP

Expiratory flow limitation exists when increasing expiratory effort fails to increase the expiratory flow rate. This can been seen when a patient exhales along the same flow-volume curve during quiet, tidal breathing as they do during a forced expiratory effort. Tidal expiratory flow limitation (EFLt) is a key concept in understanding dyspnea, hyperinflation and orthopnea in patients with COPD and in assessing the functional severity of COPD.

EFLt_FVL 

The notion that EFLt could be detected through flow-volume loops was proposed in the 1960’s but subsequent research has shown this approach to be unreliable for a variety of moderately esoteric reasons which include the differences in static lung recoil and airway resistance that occur following a deep inhalation, differences in time-dependent lung emptying and the viscoelastic forces in the lung. When tidal flow limitation as seen on flow-volume loops is compared to other techniques it is apparent that flow-volume loops overestimate the presence of EFLt by approximately one-third.

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