Chest Wall Mechanics in COPD
In moderate and severe Chronic Obstructive Pulmonary Disease (COPD), the increased mechanical loads due to airflow limitation and the geometrical changes of the thorax due to lung hyperinflation alter the structure of the chest wall and the function of the respiratory muscles. In patients with severe hyperinflation and COPD the diaphragm retains the intrinsic properties to generate pressure and its capacity to generate tidal volume during breathing at rest is preserved. However, the increase of respiratory drive (motoneuronal discharge frequency to the diaphragm) and remodelling of the fibre types represent respectively functional and structural adaptations of this muscle to the disease. The abdominal expiratory muscles play an important role in the presence of COPD. Expiratory muscle activity has been observed in a significant portion of patients both at rest and during exercise. Even if the functional significance of expiratory muscle activity is still to be completely understood, there is increasing body of evidence that, in addition to other important factors like dynamic hyperinflation and the related dyspnoea or deconditioning of peripheral muscles, chest wall mechanics, in particular excessive expiratory pressures, can be a potent factor contributing to exercise limitation in COPD.
Keywords: Chest wall, COPD, diaphragm, abdominal muscles, resting breathing, exercise
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