Background: The diaphragm is the major muscle of respiration and the second most important muscle in the human body after the heart. Because the body relies so much on the diaphragm for respiratory function, understanding how many different disease processes ultimately result in diaphragm dysfunction is important.

A concomitant respiratory dysfunction exists any time a decrease in diaphragmatic function is present. The body possesses inherent mechanisms of compensation for decreased diaphragmatic function, but none of these processes can successfully prevent respiratory compromise if excursion of the diaphragm is moderately diminished or simply absent.

The easiest approach to diaphragmatic problems is to observe both the neurologic and anatomic processes that result in decreased function. Neurologic problems of the diaphragm occur when a traumatic injury or disease process decreases or terminates the impulse of respiratory stimuli originating in the brain. Anatomic disorders decrease the integrity of the musculature of the diaphragm, thus decreasing its excursion. Both anatomic and neurologic problems related to the diaphragm ultimately result in the inability of the diaphragm to provide adequate negative intrathoracic pressure, thereby decreasing the amount of oxygen provided to the alveoli.

Anatomy of the diaphragm

The diaphragm is a modified half dome of musculofibrous tissue that separates the thorax from the abdomen. Four embryologic components make up the formation of the diaphragm: the septum transversum, 2 pleuroperitoneal folds, cervical myotomes, and the dorsal mesentery. Development begins during the third week of gestation and is completed by the eighth week. Failure in the development of the pleuroperitoneal folds and subsequent muscle migration results in congenital defects (see Disorders of anatomy).

The muscular origin of the diaphragm is from the lower 6 ribs bilaterally, the posterior xiphoid process, and from the external and internal arcuate ligaments. A number of different structures traverse the diaphragm, but 3 distinct apertures allow the passage of the aorta, esophagus, and the vena cava. The aortic aperture is the lowest and most posterior of the openings lying at the level of the 12th thoracic vertebra. The aortic opening also transmits the thoracic duct and, sometimes, the azygous and hemiazygous veins. The esophageal aperture is surrounded by diaphragmatic muscle and lies at the level of the 10th thoracic vertebra. The vena caval aperture is the highest of the 3 openings and lies level to the disk space between the eighth and ninth thoracic vertebrae.

Arterial supply to the diaphragm comes from the right and left phrenic arteries, the intercostal arteries, and the musculophrenic branches of the internal thoracic arteries. Some arterial blood is provided from small branches of the pericardiophrenic arteries that run with the phrenic nerve, mainly where the nerves penetrate the diaphragm. Venous drainage occurs via the inferior vena cava and azygous vein on the right and the adrenal/renal and hemizygous veins on the left.

The diaphragm receives its sole neurologic impulse from the phrenic nerve, which originates primarily from the fourth cervical ramus but also has contributions from the third and fifth rami. Originating around the level of the scalenus anterior muscle, the phrenic nerve courses inferiorly through the neck and thorax before reaching its end point, the diaphragm. Because the phrenic nerve has such a long course before reaching its final destination, any processes that disrupt the transmission of neurologic impulses through the nerve directly affect the diaphragm.

Pathophysiology:

Disorders of innervation

During normal respiration, the brain stem sends a nervous impulse to the third through fifth spinal levels, which then give off dorsal rami that further convalesce to form the phrenic nerves bilaterally. The phrenic nerves then traverse the neck and thorax and innervate the diaphragm. The successful impulse of respiratory stimulus from the brain to the diaphragm can be compromised by a myriad of entities.

Traumatic injury to the head and/or brain stem prevents nerve signals from reaching the phrenic nerve. Generally, injuries that affect the brain and brain stem are catastrophic, with chances of survival being grim.

Injuries or disease processes that affect the respiratory nervous impulse along its long course are widely described. A number of distinct entities, including trauma, spinal cord disorders, syringomyelia, poliomyelitis, and different motor neuron diseases, decrease the impulse of stimuli to the cervical spinal cord.

Peripheral phrenic nerve injuries result from damage to the nerve along its path in the cervical area or the thorax. A number of clinical entities can affect the phrenic nerve directly, including trauma, open heart surgery or thoracic surgery, chiropractic cervical spine manipulation, radiotherapy, demyelinating diseases (eg, Guillain-Barré syndrome), neoplasm, uremia, brachial plexus stretch injury or neuritis, lead neuropathy, postinfectious neuropathies, and many other processes.

Disorders of anatomy

Anatomic disorders of the diaphragm are typically classified into 2 broad categories: congenital and acquired. Congenital diaphragmatic hernias occur when the muscular entities of the diaphragm do not develop normally, usually resulting in displacement of abdominal components into the thorax. The most common cause of acquired diaphragmatic disorders is trauma; however, consider several other important entities when observing anatomic defects of the diaphragm in adults.

Bochdalek hernias represent the majority of congenital diaphragmatic hernias. The major defects in Bochdalek hernias are posterolateral defects of the diaphragm, which result in either failure in the development of the pleuroperitoneal folds or improper or absent migration of the diaphragmatic musculature. Animal models suggest that one potential cause of congenital diaphragmatic hernias is abnormalities of the retinoid system that potentially result from maternal vitamin A deficiency. Patients with congenital diaphragmatic hernias generally present in the neonatal period and have a mortality rate of 45-50%. The morbidity and mortality associated with congenital diaphragmatic hernias relate mostly to hypoplasia of the lung on the affected side. Thus, timely diagnosis and proper management remains the key ingredient to survival.

Traumatic diaphragmatic rupture occurs secondary to both blunt and penetrating trauma. Incidence of diaphragmatic rupture is 0.8-1.6% in patients admitted to the hospital for blunt trauma. The major etiologies of diaphragmatic rupture are motor vehicle accidents and penetrating trauma from gunshot and stab wounds. Several theories have been postulated regarding the mechanism of rupture due to blunt trauma, including shearing of a stretched membrane, avulsion of the diaphragm from its points of attachment, and sudden force transmission through viscera acting as a viscous fluid. Left-sided rupture is more common than right-sided rupture (68.5% vs 24.2%) because of both hepatic protection and increased strength of the right hemidiaphragm. However, increased left-sided hernias may also result from weaknesses in points of diaphragmatic embryologic fusion.

Mortality/Morbidity: Morbidity and mortality resulting from diaphragmatic disorders are associated with the etiology of the dysfunction. Individuals with anatomic defects are much more likely to survive than individuals with unresolving defective or absent neurologic impulses. Persons with unilateral dysfunction are much more likely to remain asymptomatic when compared with individuals with bilateral involvement.

• Patients with neurologic involvement generally recover if dysfunction is not due to neuropathic process. Recovery can take up to 2 years or longer.

• Patients with anatomic defects generally do well once the defect is repaired. The outcome of neonates with congenital diaphragmatic hernias generally relates to the pulmonary development after repair of the hernia.

• Patients with congenital diaphragmatic hernias generally present in the neonatal period and have a mortality rate of 45-50%. The morbidity and mortality associated with congenital diaphragmatic hernias relate mostly to hypoplasia of the lung on the affected side. Thus, timely diagnosis and proper management remains the key ingredient to survival.

History: Background information is of prime importance when considering dysfunctions of the diaphragm. An adequate history is essential to help narrow potential causes. Even so, an etiology for diaphragmatic dysfunction is never found in 50-60% of patients.

• Congenital hernias

• Respiratory distress and/or cyanosis may occur within the first 24 hours of life.

• If the defect is small enough, patients often remain asymptomatic for years and even decades.

• Traumatic rupture

• The acute phase manifests with abdominal pain, concurrent intra-abdominal and intrathoracic injuries, respiratory distress, and cardiac dysfunction.

• Latent-phase symptoms include upper GI complaints, pain in the left upper quadrant or chest, pain in the left shoulder, dyspnea, and orthopnea.

• The gastrointestinal obstructive phase manifests with nausea and vomiting with unrelenting abdominal pain, prostration, and respiratory distress.

• Neurologic causes

• Fifty percent of patients with unilateral paralysis are asymptomatic. Manifestations include mild exertional dyspnea, generalized muscle fatigue, chest wall pain, and resting dyspnea while lying with paralyzed side down. Symptoms are generally more severe in patients with concomitant lung disease.

• Bilateral paralysis manifests with shortness of breath, severe exertional dyspnea, and marked orthopnea.

Physical: Physical findings on examination vary depending on the etiology.

• Congenital hernias

• Right-sided heart

• Decreased breath sounds on affected side

• Scaphoid abdomen

• Auscultation of bowel sounds in the thorax

• Traumatic rupture

• Marked respiratory distress

• Decreased breath sounds on affected side

• Palpation of abdominal contents upon insertion of chest tube

• Auscultation of bowel sounds in chest

• Paradoxic movement of abdomen with breathing

• Neurologic causes

• Decreased breath sounds

• Generalized or focal neurologic deficits

• Paralysis

Causes: The etiology of diaphragmatic dysfunction is most easily separated into anatomic or neurologic causes.

• Anatomic defects

• Congenital defects - Bochdalek hernia, Morgagni hernia, eventration of the diaphragm, and diaphragmatic agenesis

• Acquired defects - Traumatic rupture, penetrating injuries, idiopathic etiologies, and iatrogenic responses to surgery or other invasive procedures

• Innervation defects

• Cerebral stroke

• Spinal cord disorders - Trauma to the cervical spinal cord, syringomyelia, poliomyelitis, and motor neuron disease

• Phrenic nerve neuropathy - Trauma to the phrenic nerve from surgery, radiation, or tumor; Guillain-Barré syndrome; brachial plexus neuritis; diabetic, nutritional, and alcoholic neuropathy; vasculitic neuropathy; lead and poison neuropathy; and infection-related nerve injury (eg, diphtheria, tetanus, typhoid, measles, botulism)

• Myasthenia gravis

• Muscular disorders - Myotonic dystrophies, Duchenne muscular dystrophy, metabolic myopathies, and polymyositis

• Idiopathic etiologies

Other Problems to be Considered:

Fractures, Cervical Spine
Guillain-Barré Syndrome
Myasthenia Gravis
Cervical fracture
Cerebral hemorrhage or ischemia
Numerous neuropathies
Injury to phrenic nerve from trauma
Injury to phrenic nerve from neoplasm
Injury to phrenic nerve from surgery (most commonly from cardiac surgery due to cold cardioplegia)

Lab Studies:

• Laboratory studies are limited to discovery of neuropathic causes of diaphragmatic dysfunction.

Imaging Studies:

• Chest radiography

• Neurologic impairment manifests radiographically with elevation of the diaphragm (unilateral or bilateral), mediastinal shift on inspiration, and diminished, absent, or paradoxic movements on inspiration. Chest radiographs may exhibit cervical or thoracic mass that encompasses the phrenic nerve.

• Congenital defect or traumatic rupture is demonstrated roentgenographically with abdominal contents in the thorax on the affected side. A nasogastric tube in the thorax may be mistaken for a massive hemothorax. Thus, palpation of lung parenchyma and/or abdominal viscus within the thorax before insertion of a chest tube into the patient with trauma is always important.

• Fluoroscopy

• Up to 6% of the healthy population has paradoxic movement of a hemidiaphragm on a deep inspiratory effort against a closed airway (sniff test) as a normal finding.

• The sniff test is considered positive if a 2-cm or longer excursion is present and the whole leaf of the hemidiaphragm, in the oblique view, is involved.

Other Tests:

• Pulmonary function tests, including maximum inspiratory pressures, transdiaphragmatic pressure measurement, and vital capacity, in both upright and supine positions help the clinician to determine whether diaphragmatic dysfunction is present and/or to determine the degree of respiratory compromise experienced by the patient in different positions.

• Phrenic nerve conduction studies are used to assess the latency of conducting nervous impulses along the course of the nerve. This helps localize lesions to one side or the other and helps the clinician to decipher whether the condition is a bilateral phenomenon. This test is not generally available and may require referral to a center that is able to provide this service.

Medical Care: Focus medical care on the etiology of the dysfunction. In anatomic causes and defects, the only treatment option is surgical repair. Once a nontraumatic etiology is considered, the most important next step is to discover the cause. Neurologic processes, depending on the etiology, can generally be managed medically.

• Supportive management

• Many patients with severe dysfunction need ventilatory support. Depending on the etiology of the disease, some patients only require short-term support, while others may require life-long ventilatory breathing.

• If the phrenic nerve is intact and the problem lies in actually transmitting an impulse to the nerve, phrenic nerve or diaphragmatic pacing may be useful modalities in the treatment of this subset of patients.

• Neurologic

• Once a diagnosis of neurologic dysfunction is made, ordering studies to determine the cause is vital.

• A number of neurologic etiologies can be managed medically, but discovering the cause often becomes a challenge.

Surgical Care: Surgically manage anatomic defects in the diaphragm. The type of surgical intervention depends on the anatomic defect or problem.

• Congenital defects: Manage congenital diaphragmatic defects through transabdominal primary surgical repair.

• Acquired defects: Manage acquired diaphragmatic defects (ie, traumatic rupture, late-onset congenital diaphragmatic defect) by thoracoscopic plication of the hemidiaphragm.

• Phrenic nerve injury

• Primary repair of phrenic nerve damage from trauma can be attempted but does not generally restore function. With expectant treatment, few patients regain phrenic nerve function.

• Manage injury from a tumor by resection of the tumor encasing the phrenic nerve, which yields good results. Most patients regain function of the nerve.

• Cold phrenic nerve injury during cardiac surgery generally resolves with expectant management.

• Spinal cord injury or phrenic nerve injury: Diaphragmatic pacing is new technology that allows the placement electrodes within the diaphragm that stimulate the diaphragm to contract. This can be done either transthoracically or transabdominally, with more recent literature supporting the used of laparoscopy and thoracoscopy.

Further Outpatient Care:

• Once an anatomic defect is corrected, the patient should undergo periodic chest radiography and assessment of pulmonary function. Although spontaneous recurrence of a repaired diaphragmatic hernia is low, small defects in the repair site have been reported; therefore, surveillance is important.

• If dysfunction was secondary to a tumor encroaching on the phrenic nerve, maintaining close follow-up contact with the patient is important to ensure that the mass has not recurred.

Complications:

• Anatomic defects may lead to respiratory failure, incarceration or strangulation of bowel, or hypoplasia of the lung in congenital defects.

• Neurologic problems may lead to respiratory failure.

Prognosis:

• Patients with anatomic repairs

• The prognosis for patients with anatomic repairs from traumatic rupture directly correlates with the extent of concomitant injuries.

• Neonates generally have a good prognosis after repair of congenital diaphragmatic hernias, but the prognosis is directly related to the development of the lung on the affected side.

• Patients with neurologic conditions

• The prognosis for patients with neurologic conditions generally correlates with etiology.

• Persons with high cervical spine fractures generally fare worse than individuals with transient neuropathies such as Guillain-Barré syndrome.

More of this article can be found at eMedicine - Diaphragm Disorders : Article by Jason M Johnson, DO