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Causes and diagnosis of unilateral diaphragmatic paralysis and eventration in adults

Bartolome R Celli, MD
Section Editor
Talmadge E King, Jr, MD
Deputy Editor
Geraldine Finlay, MD


Ventilation depends upon the ability of the respiratory pump to move air in and out of the gas exchanging portion of the lungs. The dome-shaped diaphragm is the most important inspiratory muscle [1-3]. The other main muscles of inspiration are the scalenes, external intercostals, and sternomastoids. The muscles of expiration are the internal intercostals and the muscles of the abdominal wall (including the rectus abdominus, internal and external obliques, and transversus abdominus). Normal diaphragmatic function is discussed separately. (See "Causes and diagnosis of bilateral diaphragmatic paralysis", section on 'Normal diaphragm function'.)

In addition to its role in the respiratory pump, the diaphragm also serves as a mechanical barrier between the abdominal and thoracic cavities and maintains the pressure gradient between the cavities.

The causes and diagnostic evaluation of unilateral diaphragmatic paralysis and diaphragmatic eventration in adults will be reviewed here. The clinical manifestations and evaluation of respiratory muscle weakness due to neuromuscular disease, the evaluation and management of bilateral diaphragmatic paralysis in adults, disorders of control of ventilation, and the evaluation and management of diaphragm paralysis in the newborn are reviewed separately. (See "Respiratory muscle weakness due to neuromuscular disease: Clinical manifestations and evaluation" and "Causes and diagnosis of bilateral diaphragmatic paralysis" and "Disorders of ventilatory control" and "Diaphragmatic paralysis in the newborn" and "Treatment of diaphragmatic paralysis".)


The left and right sides of the diaphragm are innervated by the ipsilateral phrenic nerves, which derive from cervical nerve roots three, four, and five [4]. Each nerve divides into four trunks that innervate the anterolateral, posterolateral, sternal, and crural portions of the diaphragm. Interruption or injury to one of the phrenic nerves results in unilateral diaphragmatic paralysis [5-9]. Normal diaphragmatic structure and function are described separately. (See "Causes and diagnosis of bilateral diaphragmatic paralysis", section on 'Normal diaphragm function'.)

Depending upon the degree of diaphragmatic compromise, the other hemidiaphragm or the accessory muscles of respiration assume some or all the work of breathing. This compensation is achieved by more intense contraction of the accessory muscles and by the progressive recruitment of other, less important accessory inspiratory muscles (sternomastoid, trapezius, latissimus dorsi, and pectoralis minor and major). Patients may also recruit abdominal muscles to augment exhalation, which forces the respiratory system to a lower volume (below functional residual capacity) at end-exhalation. The low volume increases the elastic recoil energy in the chest wall, assisting the next inspiration.

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Literature review current through: Nov 2017. | This topic last updated: Nov 27, 2017.
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