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КЛИНИЧЕСКИЕ ПРОЯВЛЕНИЯ ПАРЕЗОВ И ПАРАЛИЧЕЙ ДИАФРАГМЫ
Isolated diaphragmatic weakness, without weakness of other muscles of respiration, may have only subtle clinical manifestations.10 Unilateral diaphragmatic paralysis is often asymptomatic, although some patients have dyspnea on exertion.11 Obviously, unilateral diaphragmatic weakness superimposed on intrinsic lung disease results in worsened symptoms. Physical examination findings may include decreased or paradoxical diaphragmatic excursion, reduced breath sounds at the base of the lung, and asymmetric motion of the abdominal wall.
Bilateral diaphragmatic paralysis presents with dyspnea on exertion and orthopnea. In the upright position, the accessory muscles are able to achieve sufficient minute ventilation in the absence of any diaphragmatic activity, although the diaphragm may be pulled upwards into the thorax to some degree by the negative intrathoracic pressure. However, when the patient reclines and the effect of gravity is removed, the abdominal contents displace the diaphragm into the thorax, leading to low tidal volumes and atelectasis, and hence orthopnea. In addition to the upward displacement of the weak diaphragm during recumbency, the movement of abdominal contents into the thorax expands the rib cage, and places the intercostal muscles at a suboptimal length for contraction, which exacerbates respiratory muscle weakness. In contrast to the orthopnea characteristic of congestive heart failure, the orthopnea of diaphragmatic paralysis occurs immediately after the patient is placed in the supine position. Interestingly, the presence of orthopnea, and not the degree of dyspnea, correlates with diaphragmatic strength.1 Along the same lines, patients often experience dyspnea when submerged in water (eg, while swimming). The deeper the water into which the erect patient is submerged, the higher the pressure on the abdomen, which leads to inward displacement of the abdominal wall and upward displacement of the diaphragm.12,13
In bilateral diaphragmatic paralysis, the physical examination can be impressive. There is often rapid, shallow breathing and use of accessory muscles. Dullness to percussion at the lung bases is related to atelectasis due to elevated hemidiaphragms. If assessed through percussion, diaphragmatic excursion will be decreased. Paradoxical inward movement of the abdomen on inspiration, which is particularly evident in the supine position, is highly suggestive of diaphragmatic weakness. In the setting of diaphragmatic paralysis, as the accessory muscles expand the rib case, the negative intrathoracic pressure is transmitted to the abdomen, leading to upward displacement of the paralyzed diaphragm into the thorax and paradoxical, inward movement of the abdominal wall. Severe bilateral diaphragmatic paralysis is usually associated with paradoxical abdominal movement, although patients with milder paresis or unilateral diaphragm paralysis often have normal abdominal movement.1If paradoxical abdominal movement is not apparent by simple inspection, palpation under the costal margins can evaluate for descent of the diaphragm during inspiration.
With diaphragmatic weakness, but not complete paralysis, the muscle can fatigue. This may lead to a breathing pattern in which the diaphragm and the accessory muscles alternate between abdominal and rib cage breathing (respiratory alternans ).14
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