Breathlessness in Patients with Chronic Airflow Limitation: Intrinsic Mechanical Loading and Breathlessness in CAL
Ventilatory responses for a given metabolic load were, on average, 33 percent higher in the SB group. The two groups were well matched for resting pulmonary function parameters such as FEVi, but values for single-breath diffusion capacity in the SB group were significantly lower by an average of 50 percent. Not surprisingly, heightened ventilatory slopes in the SB group were associated with significantly higher fixed physiologic dead space (Vd/Vt) and greater gas exchange abnormalities, especially during exercise. Canadian neighbor pharmacy further Thus, patients with CAL with greater ventilation-perfusion inhomogeneity and wasted ventilation have relatively diminished ventilatory reserve and experience greater levels of breathlessness at a given external power output.
Despite the linear relationship between breathlessness and the ventilatory index, there remains substantial intersubject variability in breathlessness for a given Ve/MBC.7 The source of this variability is multifactorial and likely includes variability in the extent of intrinsic mechanical loading of the ventilatory muscles, their contractile strength, and functional characteristics. Variation in the extent of dynamic airway compression is also a potential contributing factor. Other little studied factors that may contribute to intersubject variability in exertional breathlessness in CAL include variation in cardiorespiratory receptor activation in the presence of raised pulmonary artery pressure or concomitant left ventricular dysfunction. In addition, variability in behavioral responses to ventilatory stress is undoubtedly important.
The most important mechanical abnormality in patients with CAL is expiratory flow limitation. One possible consequence of expiratory flow limitation is dynamic airway compression (DC) that occurs if transpulmonary pressures exceed the critical pressure at which flow is maximal (Pcrit).” It has been postulated that DC and distortion of the airways mouth-wards from the flow-limiting segment contributes to breathlessness in CAL.
Category: Respiratory Symptoms
Tags: breathlessness, chronic airflow limitation, copd, dynamic compression, dynamic hyperinflation, exercise