Capnographic Identification of End-Expiratory Flow Limitation

This study evaluated 6 healthy subjects exhaling from total lung capacity to residual volume at several set constant rates. We measured the volumes of flow limitation (VFL) and phase 5 (VP5) for CO2 and N2. A distinct phase 5 occurred shortly after eEFL for both gases. Increased expiratory flow rate resulted in parallel increases in VFL and VP5. The two quantities differed on average by the volume of dead space. These data suggest that phase 5 on capnography identifies eEFL with a small delay resulting from transit of expired gas through dead space. Following phase 5 by volumetric capnography could be useful for monitoring anesthetized patients, who in some circumstances may have lung volumes close to residual volume. eEFL could be treated with lung volume-increasing maneuvers, such as positive end-expiratory pressure.
Source: Respiratory Physiology and Neurobiology - Category: Respiratory Medicine Source Type: research