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 latest article in our Current Concepts review series includes videos showing ultrasonography of normal and paralyzed diaphragms, available now at NEJM.org
The mechanical action of the diaphragm is best understood by considering its anatomy and its attachment to the chest wall. The diaphragm abuts the lower rib cage in a region referred to as the zone of apposition. As the diaphragm contracts, the abdominal contents are displaced caudally, abdominal pressure increases in the zone of apposition, and the lower rib cage expands. Disease processes that interfere with diaphragmatic innervation, contractile properties, or mechanical coupling to the chest wall can result in diaphragmatic dysfunction.
• What is the innervation pattern of the diaphragm?
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.
• What is the most characteristic sign of diaphragmatic dysfunction on physical examination?
The most characteristic physical sign of diaphragmatic dysfunction is the abdominal paradox, which is the paradoxical inward motion of the abdomen as the rib cage expands during inspiration. This disordered breathing pattern results from compensatory use of the accessory inspiratory muscles of the rib cage and neck. When these muscles contract and lower pleural pressure, the weakened or flaccid diaphragm moves in a cephalad direction and the abdominal wall moves inward. This paradoxical breathing pattern is most easily seen with the patient in the supine position. The abdominal paradox is typically observed when the maximum transdiaphragmatic pressure that the patient can generate against a closed airway is less than 30 cm of water; it rarely occurs in unilateral diaphragmatic paralysis. When the abdominal paradox is present in unilateral diaphragmatic paralysis, it suggests generalized weakness of the respiratory muscles.
Morning Report Questions
Q: How does one diagnose diaphragmatic dysfunction?
A: Chest radiographs may reveal elevated hemidiaphragms and basal subsegmental atelectasis. Although chest radiography is a reasonably sensitive tool for detecting unilateral diaphragmatic paralysis (90%), its specificity is unacceptably low (44%). Fluoroscopy of the diaphragm has been extensively used to evaluate diaphragmatic function. A “sniff test” consists of assessing the motion of the diaphragm during a short, sharp inspiratory effort through the nostrils. Descent of the diaphragm will be seen in persons without the disorder. With unilateral diaphragmatic paralysis, there is a paradoxical (cephalad) movement of the paralyzed hemidiaphragm. Pulmonary function tests may also be helpful. A decrease in vital capacity of 30 to 50% when the patient is supine supports the diagnosis of bilateral diaphragmatic paralysis, whereas a decrease in vital capacity of 10 to 30% may be seen with mild diaphragmatic weakness or unilateral diaphragmatic paralysis. Ultrasonography can also distinguish a functioning from a nonfunctioning diaphragm; it can be used to diagnose both unilateral and bilateral diaphragmatic paralysis and to monitor recovery of the paralyzed diaphragm.
Q: What are the treatment options for diaphragmatic dysfunction?
A: Treatable causes of diaphragmatic dysfunction include myopathies related to metabolic disturbances such as hypokalemia, hypomagnesemia, hypocalcemia, and hypophosphatemia. Correction of electrolyte and hormonal imbalances and avoidance of neuropathic or neuromuscular blocking agents can restore diaphragmatic strength. Idiopathic diaphragmatic paralysis or paralysis due to neuralgic amyotrophy may improve spontaneously. When diaphragmatic dysfunction persists or progresses, ventilatory support, ranging from nocturnal to continuous, may be needed. Indications for initiating nocturnal noninvasive ventilation in patients with symptoms include a partial pressure of arterial carbon dioxide of 45 mm Hg or higher in daytime, oxygen saturation of 88% or less for 5 consecutive minutes at night, or progressive neuromuscular disease with a maximal static inspiratory pressure of less than 60 cm of water or a forced vital capacity of less than 50% predicted. In unilateral paralysis plication of the diaphragm may be used to render the flaccid hemidiaphragm taut by oversewing the membranous central tendon and the muscular components of the diaphragm. Phrenic pacing has the potential to provide full ventilatory support for ventilator-dependent patients who have bilateral diaphragmatic paralysis and intact phrenic nerves.