Dysfunction of the Diaphragm

Dysfunction of one or both hemidiaphragms is an underdiagnosed cause of dyspnea. Weakness or paralysis may be seen during mechanical ventilation, after surgery or trauma, with metabolic or inflammatory disorders, and with myopathy, neuropathy, or diseases causing lung hyperinflation. The diaphragm is the dome-shaped structure that separates the thoracic and abdominal cavities. It is the principal muscle of respiration, is innervated by the phrenic nerves that arise from the nerve roots at C3 through C5, and is primarily composed of fatigue-resistant slow-twitch type I and fast-twitch type IIa myofibers. 1 Its mechanical action is best understood by considering its anatomy and its attachment to the chest wall. 2 The diaphragm abuts the lower rib cage in a region referred to as the zone of apposition (Figure 1). As the diaphragm contracts, the abdominal contents are displaced caudally, abdominal pressure increases in . . .