Breathlessness in Patients with Chronic Airflow Limitation: Dynamic Airway Compression and Breathlessness in CAL
The second consequence of expiratory flow limitation is dynamic lung hyperinflation (DH) comments canadian family pharmacy. In the setting of increased ventilatory demand when expiratory flow is reduced and expiratory time is insufficiently long, inspiration begins before lung volume has declined to the level normally dictated by the balance of static recoil of the lung and chest wall and end-expiratory lung volume (EELV) increases. The potential sensory consequences of DC and DH are considered below.
To examine the effects of DC on respiratory sensation, we applied a flow-proportioned negative pressure (expiratory assist) at the mouth during expiration using a specially modified rolling-seal spirometer during tidal breathing in nine demonstrably flow-limited patients with severe CAL (FEVi=27 ±9 percent predicted, mean±SD). Accordingly, we induced DC by transmural airway pressure manipulation without altering pressure-flow relationships or airway mechanics upstream from the flow-limiting segment.
Expiratory assist (EA) resulted in unpleasant respiratory sensation, which in many subjects was anecdotally akin in quality to their previous experience of breathlessness. By contrast, EA in normal subjects, in whom DC was not induced, resulted in a pleasant sensation of unimpeded expiration. The mechanism by which airway distortion and compression results in unpleasant respiratory sensation was not precisely elucidated in that study but may result from the stimulation of sentient airway mechanoreceptors that are distributed in abundance throughout the upper airways. Alternatively, DC could contribute to breathlessness indirectly via stimulatory influences on ventilation in these severely mechanically compromised patients: a mean EA of —9.7 cm H2O/L/S resulted in a mean increase of 12 percent in Ve.
Although DC represents a potential source of breathlessness in CAL, it would appear that significant DC is seldom encountered at rest or during moderate activity in such patients.
Category: Respiratory Symptoms
Tags: breathlessness, chronic airflow limitation, copd, dynamic compression, dynamic hyperinflation, exercise