Disorders of the Diaphragm

Tony S. Han

The diaphragm is the principal muscle of respiration during quiet breathing. It also serves as the barrier between the thoracic and abdominal compartments. Proper integrity of the diaphragm is important in maintaining negative pressure within the thoracic cavity. Disorders of the diaphragm include paralysis, weakness, eventration, herniation, and rupture.

PARALYSIS OF THE DIAPHRAGM

Paralysis is the most important clinical condition affecting the diaphragm. It can be discovered incidentally but often presents with dyspnea on exertion or dyspnea when in the supine position. The right and left phrenic nerves originate from the third, fourth, and fifth cervical roots. They run in the lateral compartment of the neck, enter the thorax posteriorly, and then run anteriorly over the pericardium to finally innervate the hemidiaphragms. Cooling of the heart during cardiac surgery can damage the phrenic nerves or diaphragm leading to paralysis. Paralysis usually occurs on the left side and is often temporary. The overall incidence is about 2%. Other causes of paralysis include tumor invasion, surgical section, trauma, and post-viral neuropathy. Often, the exact etiology is unknown. Rare causes include neck irradiation, hypothyroidism, post-polio syndrome, acid maltase deficiency, Guillain–Barré syndrome, systemic lupus erythematosus, and malnutrition. Bilateral diaphragmatic paralysis is usually the result of cervical spinal cord trauma. Bilateral involvement is also seen with generalized neuromuscular disorders such as amyotrophic lateral sclerosis.

Patients with diaphragmatic paralysis present with dyspnea on exertion and orthopnea. Other conditions such as obstructive lung disease, congestive heart failure, thromboembolic disease, and pulmonary arterial hypertension must be excluded. Symptoms can be progressive and lead to significant disability. Sometimes the dyspnea is worse with immersion in water due to increased pressure on the abdomen. With diaphragmatic paralysis, the intercostal and the accessory muscles become the chief muscles of inspiration. Orthopnea occurs due to the effect of hydrostatic pressure of abdominal contents on the diaphragm and decreasing vital capacity. Also, there may be paradoxical elevation of the paralyzed hemidiaphragm during inspiration, which compromises ventilation. On physical examination, patients with bilateral diaphragmatic paralysis often show prominent activity of the accessory muscles of inspiration (i.e., intercostals, scalene, and sternocleidomastoids), because their inspiration results primarily from elevation of the rib cage by these muscles. Patients often favor the upright position, from which they can fixate their pectoral girdle and use their pectoral muscles to elevate the chest wall and breathe more efficiently. When supine, they may display a classic paradoxical inward motion of the anterior abdominal wall during quiet inspiration. Percussion of the chest wall before and after inspiration may reveal decreased excursion of the hemidiaphragms.

Chest radiographs may show elevation of the paralyzed hemidiaphragm. This finding is sensitive (0.90) but not specific (0.44). Thus, many patients found to have incidental elevation of the hemidiaphragm on chest radiograph have normal lung function. Pulmonary function testing in diaphragmatic paralysis reveals a reduced forced vital capacity (FVC) and reduced forced expiratory volume in 1 second (FEV₁) with preserved FEV₁/FVC ratio. In addition, total lung capacity (TLC), vital capacity, inspiratory capacity, and maximal inspiratory pressure are all reduced. Unilateral paralysis reduces TLC and maximal inspiratory pressure by 20% to 25%. A low inspiratory capacity that decreases still further in the supine position suggests diaphragmatic paralysis.

The definitive diagnosis of diaphragmatic paralysis has traditionally rested on fluoroscopic demonstration of diminished, absent, or paradoxical upward motion during normal inspiration. The “sniff maneuver” with a closed mouth is used to enhance this paradoxical upward movement during a quick inspiration. With unilateral disease, the normal diaphragm moves downward while the paralyzed diaphragm moves paradoxically upward. In cases of bilateral paralysis, the diaphragms may move together and appear to be functioning normally (though not in the appropriate direction during inspiration and expiration), thus producing a false-negative fluoroscopic result. A more comprehensive evaluation can be made by inserting balloon catheters to record gastric and esophageal pressures to measure transdiaphragmatic pressure (Pdi). Pdi should increase with inspiration and the abdomen should move outward. The failure to increase Pdi, or the generation of greater Pdi by inward motion of the abdomen, suggests diaphragmatic paralysis. Magnetic phrenic nerve stimulators applied to the neck coupled with these pressure measurements have been used to definitively diagnose paralysis. Absence of pressure change in response to nerve stimulation is diagnostic. Recent studies have also suggested using two-dimensional B-mode ultrasound to assess diaphragm function. An ultrasound transducer is placed in the eighth or ninth intercostals space in the midaxillary line. Diaphragmatic thickness is measured at functional residual capacity and TLC to indicate the degree of thickening. Less than a 20% change in thickness may indicate diaphragmatic paralysis.

Patients with diaphragmatic paralysis may be at higher risk for sleep disordered breathing, particularly during REM sleep. Compared to typical obstructive sleep apnea patients, their respiratory events seem to be primarily central hypopneas associated with more severe oxyhemoglobin desaturation. This is apparently due to respiratory muscle fatigue and mechanical disadvantage. It may be worthwhile to pursue sleep testing, particularly if the patient has significant daytime symptoms.

Diaphragmatic paralysis not related to spinal injury may improve spontaneously over a period of months to years. Treatment of diaphragmatic paralysis with pacing may be indicated in central paralysis when the phrenic nerve and diaphragmatic muscle are preserved. Electrodes are surgically implanted around the phrenic nerve, and electronic signals are generated using an external radio-wave source worn by the patient. Following installation of such a pacing device, weeks or months may be required to achieve full effect if diaphragmatic atrophy has antedated pacing.

Recovery of diaphragmatic paralysis over 6 to 12 months has been described in cases of thermal injury during cardiac surgery. If there is no improvement after 12 to 24 months, surgical plication of the hemidiaphragm is a viable option for patients with significant dyspnea. The thin flaccid diaphragm is made taut with nonresorbable sutures to improve lung mechanics. The procedure can be performed either through video-assisted thoracoscopy (VATS) or thoracotomy. Long-term follow-up at 4 to 6 years indicate sustained improvement in symptoms and lung function. Alternatively, in unilateral diaphragmatic paralysis associated with brachial plexus neuritis, a few patients have responded well to valacyclovir therapy with improvement within 4 to 6 weeks.

EVENTRATION OF THE DIAPHRAGM

Eventration in the purest sense is a congenital malformation consisting of failure of muscular development of all or part of the diaphragm. It is associated with other malformations such as hypo-plastic lungs, transposition of the viscera, and chest wall and spinal abnormalities and is a surgical emergency. In common use, the term “eventration” has been used to describe chronic elevation of the hemidiaphragm from any cause including diaphragmatic paralysis. On chest roentgenogram, eventration is apt to be confused with a diaphragmatic hernia or pleuropericardial cyst. It has poor specificity for hemidiaphragm paralysis, especially if the patient is asymptomatic.

HERNIATION OF THE DIAPHRAGM

Herniation of abdominal contents through the diaphragm can occur through regions of congenital defect or weakness, including the esophageal hiatus, the posterolateral or pleuroperitoneal foramen of Bochdalek (in infants), and the retrosternal (parasternal) foramen of Morgagni (any age). Hiatal hernia (via the esophageal hiatus) is relatively common in adults. It is usually asymptomatic, but can cause retrosternal burning and pain, which are aggravated by lying flat and relieved by antacids. Occasionally, hiatal hernia can be associated with nocturnal aspiration and recurrent pneumonia.

Herniation through the posterolateral aspect of the diaphragm (foramen of Bochdalek) is the most common and serious hernia in infants. It usually presents as an acute respiratory emergency at or shortly after birth and requires immediate surgical repair.

Herniation through the foramen of Morgagni is more common in adults and is often asymptomatic. Obesity is an important predisposing factor. On chest roentgenogram, the abnormal shadow appears retrosternally, usually along the right sternal border, and can mimic a pericardial cyst.

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