Weakening and paralysis often spreads to patients' breathing muscles, and many will need ventilatory support. Also known as Lou Gehrig's disease, the progressive disease frequently causes death, often linked to pulmonary complications, within five years of diagnosis. Individual patients may have either a fast or slow rate of decline, and the onset of pulmonary symptoms may occur either early or late in the course of the disease. ALS patients may have impairment in any or all of the muscles necessary for normal ventilation, including the inspiratory muscles, expiratory muscles and muscles that control the upper airway. Weakness of the inspiratory muscles initially may lead to the loss of sigh volumes, which may cause microatelectasis and less compliant lungs.
Stiffer lungs require more diaphragmatic effort in order to take a normal tidal breath.
However, as the disease advances, there's a gradual, progressive weakening of the diaphragm and other inspiratory muscles. The increased demand for diaphragm strength at a time when the inspiratory muscles are progressively losing power puts added strain on the diaphragm and may lead to muscle fatigue, further weakening the diaphragm. Loss of upper airway muscle function in ALS can cause swallowing problems. This can lead not only to aspiration pneumonia, but also to malnutrition, which contributes to further diaphragm weakness. The loss of upper airway muscle tone may also cause upper airway obstruction, which can increase the patient's work of breathing and may produce obstructive sleep apnea in some patients.