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Diaphragm

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Musculomembranous partition between the abdomen and the thorax.

Plays a key role in respiration.

Principle muscle of respiration.

Provides the major driving force for inspiration, and accounts for approximately 65% of vital capacity in healthy patients.

It contracts and moves downward as the pectoralis minor and the intercostals muscles pull the rib cage outward.

Innervated by phrenic nerves arising from nerve roots C3 through C5.

Nerves composed from fatigue resistant slow-twitch type I and fast-twitch type IIa myofibers.

During embryological development it is made up of a septum, two pleuroperitoneal folds, cervical myotomes and a dorsal mesentery.

The pleuroperitoneal canal closes between the 8th and 10th week of gestation.

Failure of the closure of the pleuroperitoneal canal results in trapping of the bowel in the thoracic cavity, a Bochdalek hernia.

Congenital diaphragmatic hernias are birth defects that occur in approximately 1 in every 2-5000 live births.

40-50% of congenital hernias are associated with other malformations including: chromosome abnormalities, congenital heart disease, pulmonary hypoplasia, an familial syndromes.

With inspiration the central aspect of the diaphragm descends and decreases intrathoracic pressure and increased lung volume.

Abuts lower rib cage in the zone of apposition.

Diaphragmatic contraction displaces abdominal contents caudally, with increased abdominal pressure in the zone of apposition, with lower rib cage expansion.

The peripheral aspect of the diaphragm is fused to the thoracic wall and does not move.

Six structures penetrate it at specific vertebral levels and include the inferior vena cava, the aorta, the azygos vein, the thoracic duct and the esophagus.

Transversed by the vagus nerve which provides parasympathetic stimulation to the heart and lungs in the thoracic cavity and similar stimulation to the abdominal viscera.

Diseases that interfere with diaphragmatic innervation, contractraction, or mechanical coupling to the chest wall causes diaphragmatic dysfunction.

Diaphragmatic dysfunction causes dyspnea, decreased exercise capacity, sllep dosordered breathing, hypersomnia, atelectasis, impaired well being, impaired quality of life and respiratory insufficiency.

Diphragmatic dysfunction is a cause of unexplained dyspnea.

Dysfunction ranges fro partial loss of function with weakness to paralysis with comlete loss of function.

Dysfunction can involve one or both hemidiaphragms.

Each hemidiaphragm is innervated by its ipsilateral phrenic nerve derived from C3 through C5 lower motor neurons, most of which reside within the C4 spinal segment.

Dysfunction of the diaphragm may be secondary to metabolic abnormalities, inflammatory disorders, surgery, trauma, mechanical ventilation, mediastinal abnormalities, myopathies, neuropathies and pulmonary hyperinflammation.

Unilateral diaphrragmatic paralysis is generally asymptomatic, but may manifest as dyspnea with exertion, limited ability to exercise and shortness of breath when supine.

Unilateral diaphrragmatic paralysismay be an incidental finding of an elevated hemidiaphragm on chest x-ray.

Unilateral diaphragmatic paralysis associated dypnea enhanced by obesity, myopathy, cardiovascular disese, parenchymal lung disease, especially with supine position.

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