Physiological techniques for detecting expiratory flow limitation during tidal breathing

Abstract

Patients with severe chronic obstructive pulmonary disease (COPD) often exhale along the same flow-volume curve during quiet breathing as they do during the forced expiratory vital capacity manoeuvre, and this has been taken as an indicator of expiratory flow limitation at rest (EFLT). Therefore, EFLT, namely attainment of maximal expiratory flow during tidal expiration, occurs when an increase in transpulmonary pressure causes no increase in expiratory flow. EFLT leads to small airway injury and promotes dynamic pulmonary hyperinflation, with concurrent dyspnoea and exercise limitation. In fact, EFLT occurs commonly in COPD patients (mainly in Global Initiative for Chronic Obstructive Lung Disease III and IV stage), in whom the latter symptoms are common, but is not exclusive to COPD, since it can also be detected in other pulmonary and nonpulmonary diseases like asthma, acute respiratory distress syndrome, heart failure and obesity, etc. The existing up to date physiological techniques of assessing EFLT are reviewed in the present work. Among the currently available techniques, the negative expiratory pressure has been validated in a wide variety of settings and disorders. Consequently, it should be regarded as a simple, noninvasive, practical and accurate new technique.

It's Time to Reappraise the Impact of Auto-PEEP

“…6,11,12 This maneuver creates increased pleural pressure but will not further change the expiratory flow due to the closure or fixed obstruction of downstream small airways, as found in patients with COPD and obesity. 6,7,13,14 The use of manual compression of the abdomen to detect expiratory flow limitation in patients receiving mechanical ventilation is more complicated, and one study has been conducted to validate its use. 15 Critically ill patients suffer from pathophysiological conditions that may cause abdominal distention, rapid changes of body fluid in the abdomen, and intra-abdominal infections.…”

“…It can occur in patients with COPD during spontaneous breathing. 6,7 Dynamic lung hyperinflation caused by auto-PEEP worsens their inspiratory capacity because inhalation cannot be initiated from relaxation volume. [6][7][8] Consequently, inspiratory muscles must overcome the imposed load to generate inspiratory flow.…”

“…6,7 Dynamic lung hyperinflation caused by auto-PEEP worsens their inspiratory capacity because inhalation cannot be initiated from relaxation volume. [6][7][8] Consequently, inspiratory muscles must overcome the imposed load to generate inspiratory flow. 4,8 Patients with COPD are usually instructed to practice pursed lips breathing, since this is a kind of external PEEP to ameliorate the load of the inspiratory muscles.…”

“…Several methods have been validated to assess expiratory flow limitation in patients with spontaneous tidal breathing. 6 A simple noninvasive way is by the manual compression of the abdomen throughout the exhalation period. 6,11,12 This maneuver creates increased pleural pressure but will not further change the expiratory flow due to the closure or fixed obstruction of downstream small airways, as found in patients with COPD and obesity.…”

“…6 A simple noninvasive way is by the manual compression of the abdomen throughout the exhalation period. 6,11,12 This maneuver creates increased pleural pressure but will not further change the expiratory flow due to the closure or fixed obstruction of downstream small airways, as found in patients with COPD and obesity. 6,7,13,14 The use of manual compression of the abdomen to detect expiratory flow limitation in patients receiving mechanical ventilation is more complicated, and one study has been conducted to validate its use.…”