How do neuromuscular disorders cause hypoventilation?

Updated: Jul 22, 2021
  • Author: Jazeela Fayyaz, DO; Chief Editor: Guy W Soo Hoo, MD, MPH  more...
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Answer

Patients with neuromuscular disorders have a reduced vital capacity and expiratory reserve volume secondary to respiratory muscle weakness. The residual volume is maintained.

The reduction in vital capacity is greater than that which would be expected solely from the underlying respiratory muscle weakness, and these patients are likely to also have a significant reduction in lung and chest wall compliance, which further reduces vital capacity. The reduction in lung and chest wall compliance may be secondary to atelectasis and reduced tissue elasticity. In addition, the VD/VT ratio is increased due to the reduced tidal volume, and this further contributes to hypoventilation.

During sleep, ventilation decreases because of a lessening in respiratory center function. During REM sleep, atonia worsens, thus leading to more severe hypoventilation, particularly when diaphragmatic function is impaired. The effects of atonia are amplified by a low sensitivity of the respiratory centers. Nocturnal mechanical ventilation improves nocturnal hypoventilation and daytime arterial blood gases in these patients.


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