Central and transmission fatigue

Fatigue of the inspiratory muscles is caused by excessive effort relative to the muscles' strength and endurance. There is now little doubt that the pathophysiologic mechanisms that bring about fatigue are not necessarily limited to the muscle itself, but can also involve central and peripheral neural events. Central fatigue of inspiratory muscles probably plays a major role in respiratory control of patients with marginal or absent respiratory reserve, allowing them to reduce their level of dyspnea and their risk of peripheral fatigue, at the expense of carbon dioxide retention and hypoxemia. Although the role of transmission fatigue is not so clearly established, emerging evidence suggests that it too may be important in some cases of inspiratory muscle fatigue. The challenge for the future is to determine when inspiratory muscle fatigue may be active; to develop simple, specific tests for its presence and severity; to determine when it may be playing a beneficial role and when it needs treatment; and to define the most appropriate therapeutic interventions.