What does hypoventilation mean in ALS?

The term “hypoventilation” refers to reduced respiratory activity, which in turn is caused by muscular weakness of the respiratory muscles. In ALS, the degeneration of the motor nerve cells leads to paralysis (paresis) or stiffness (spasticity) of the voluntary muscles, including the respiratory muscles. In particular, the weakness of the diaphragm (the largest respiratory muscle in humans), the rib muscles (for raising and lowering the ribcage) and the neck muscles (which are also involved in raising the ribcage) are of major importance for breathing and the development of hypoventilation.

The abdominal muscles, which are involved in raising and lowering the diaphragm by controlling the pressure in the abdominal cavity, are less well known but also relevant. Overall, weakness or spasticity of the respiratory muscles leads to reduced breathing performance. As a result of hypoventilation, a lower respiratory volume is taken into the lungs – the respiratory exchange between used carbon dioxide and necessary oxygen is restricted.