Diaphragm

Introduction

The diaphragm is a dome-shaped musculotendinous structure that separates the thoracic and abdominal cavities. It plays a central role in respiration by facilitating inspiration and expiration. Beyond its respiratory function, the diaphragm contributes to venous return, intra-abdominal pressure regulation, and several reflex activities.

Anatomy of the Diaphragm

Gross Anatomy

The diaphragm is a thin, dome-shaped structure positioned at the base of the thoracic cavity. Its superior surface faces the lungs and heart, while its inferior surface is in contact with the liver, stomach, and spleen. The diaphragm is divided into three main parts based on its attachments:

• Sternal part: Attaches to the posterior aspect of the xiphoid process.
• Costal part: Originates from the inner surfaces of the lower six ribs and their costal cartilages.
• Lumbar part: Consists of right and left crura that attach to the lumbar vertebrae and arcuate ligaments.

The central tendon forms the non-muscular, fibrous portion of the diaphragm where muscle fibers converge, providing strength and flexibility.

Muscle Fiber Orientation

Muscle fibers of the diaphragm radiate from the central tendon toward the peripheral attachments. The radial arrangement allows coordinated contraction, while circumferential fibers maintain dome integrity and contribute to intra-abdominal pressure changes during respiration.

Attachments and Relations

• Sternal attachments: Posterior xiphoid process
• Costal attachments: Inner surfaces of ribs 7 to 12 and costal cartilages
• Lumbar attachments: Right and left crura connecting to lumbar vertebrae via arcuate ligaments
• Relations: Superiorly, the diaphragm is in contact with the lungs, heart, and pericardium. Inferiorly, it is related to the liver, stomach, spleen, and kidneys.

Embryology

The diaphragm develops from multiple embryonic structures, and proper formation is essential for separation of the thoracic and abdominal cavities. Abnormal development can lead to congenital defects.

• Septum transversum: Forms the central tendon and contributes to the ventral portion of the diaphragm.
• Pleuroperitoneal membranes: Close the pericardioperitoneal canals and form the posterior diaphragm.
• Dorsal mesentery of the esophagus: Gives rise to the crura and contributes to the median portion surrounding the esophageal hiatus.
• Body wall musculature: Migrating myoblasts from the lateral body walls form the peripheral muscular part of the diaphragm.

The diaphragm typically completes development by the eighth week of gestation. Failure of fusion between these components can result in congenital diaphragmatic hernias, which are clinically significant due to potential respiratory compromise.

Blood Supply and Innervation

Arterial Supply

The diaphragm receives a rich arterial blood supply from multiple sources to ensure adequate perfusion of both muscular and tendinous components.

• Musculophrenic and pericardiophrenic arteries: Branches of the internal thoracic artery, supplying the anterior and central portions.
• Inferior phrenic arteries: Arise from the abdominal aorta or celiac trunk, supplying the posterior and peripheral regions.

Venous Drainage

Venous blood from the diaphragm is primarily drained through the phrenic veins, which empty into the internal thoracic veins, inferior vena cava, and occasionally the azygos system. This extensive venous network helps maintain tissue perfusion and prevents congestion during increased intra-abdominal pressure.

Innervation

The diaphragm is mainly innervated by the phrenic nerves, which originate from the cervical spinal roots C3, C4, and C5. These nerves provide motor and sensory fibers, controlling diaphragmatic contraction and transmitting sensation from the central tendon and adjacent pleura and peritoneum. Minor contributions to peripheral diaphragmatic innervation may arise from lower intercostal nerves.

Physiology

Role in Respiration

The diaphragm is the primary muscle responsible for respiration. Its contraction and relaxation create pressure changes in the thoracic and abdominal cavities that facilitate airflow.

• Inspiration: Contraction of diaphragmatic fibers causes the dome to flatten, increasing thoracic volume and reducing intrathoracic pressure. This negative pressure allows air to flow into the lungs.
• Expiration: Diaphragmatic relaxation allows the dome to return to its resting position, decreasing thoracic volume and promoting passive exhalation. During forced expiration, abdominal muscles assist by pushing the diaphragm upward.
• Effect on intrathoracic and intra-abdominal pressures: Diaphragmatic movement modulates pressure gradients that influence venous return, organ perfusion, and gastrointestinal motility.

Accessory Functions

Beyond respiration, the diaphragm contributes to various physiological processes through pressure modulation and coordinated muscular activity.

• Coughing, vomiting, and defecation: Diaphragmatic contraction increases intra-abdominal pressure, aiding in the expulsion of air, gastric contents, or feces.
• Influence on venous return and lymphatic flow: Rhythmic diaphragmatic motion assists in venous and lymphatic circulation by creating alternating pressure gradients in the thoracic and abdominal cavities.

Clinical Significance

Diaphragmatic Paralysis or Paresis

Diaphragmatic dysfunction can result from nerve injury or neuromuscular disorders, leading to impaired ventilation and respiratory symptoms.

• Causes: Phrenic nerve injury, spinal cord trauma, poliomyelitis, multiple sclerosis, and motor neuron disease.
• Clinical features: Dyspnea, orthopnea, paradoxical abdominal movement, and reduced exercise tolerance.
• Diagnosis: Chest imaging, fluoroscopy (sniff test), and pulmonary function tests can confirm diaphragmatic weakness or paralysis.

Hernias and Defects

• Congenital diaphragmatic hernia: Results from incomplete fusion of diaphragmatic components, commonly affecting the posterolateral (Bochdalek) region, leading to abdominal organ herniation into the thoracic cavity.
• Hiatal hernia: Occurs when part of the stomach protrudes through the esophageal hiatus, potentially causing gastroesophageal reflux and respiratory symptoms.

Trauma

Traumatic injuries to the diaphragm can occur from blunt or penetrating forces, often in the context of motor vehicle accidents, falls, or stab wounds. Such injuries may be challenging to diagnose due to subtle initial symptoms and the protective effect of the rib cage.

• Blunt trauma: Sudden increases in intra-abdominal pressure can cause diaphragmatic rupture, usually on the left side.
• Penetrating trauma: Stab or gunshot wounds may directly disrupt diaphragmatic integrity, allowing abdominal contents to herniate into the thoracic cavity.
• Diagnostic challenges: Chest radiographs may be inconclusive; CT scans or MRI are often required for definitive diagnosis.

Imaging and Diagnostic Techniques

Accurate assessment of diaphragmatic anatomy and function is essential for diagnosing congenital anomalies, paralysis, or traumatic injuries.

• Chest X-ray: Initial imaging to evaluate diaphragmatic contour, elevation, or herniation of abdominal contents.
• Ultrasound: Non-invasive evaluation of diaphragmatic motion, thickness, and excursion, particularly useful in detecting paralysis or paresis.
• CT and MRI: Provide detailed anatomical imaging to identify congenital defects, traumatic ruptures, and associated organ involvement.

Surgical Considerations

Surgical intervention may be required for diaphragmatic repair, nerve dysfunction, or reconstruction in congenital or acquired conditions. Proper understanding of anatomy and function is essential for successful outcomes.

• Diaphragmatic repair techniques: Primary closure, mesh reinforcement, or patch repair depending on defect size and location.
• Phrenic nerve pacing: Used in cases of diaphragmatic paralysis to restore ventilatory function in select patients.
• Transplantation or reconstruction procedures: Rarely, diaphragmatic reconstruction may be required in extensive trauma or tumor resection.

References

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