Primary Outcome Measures:
Amyotrophic Lateral Sclerosis (ALS), also known as "Lou Gehrig's Disease", is a fatal disorder that causes breathing failure due to progressive weakness of the muscles of breathing. Breathing assist devices known as noninvasive ventilation (NIV) are offered to ALS patients when their breathing function worsens. These devices deliver breathing assistance via a mask on the nose or nose and mouth, and are thought to be particularly important to be used during sleep, when breathing often becomes more shallow and irregular. However, although these devices have become the standard of therapy in ALS patients once their lung function worsens, it remains unclear how effective these devices actually are when a patient is sleeping, partly because of the practical difficulties in applying the device properly and keeping it applied throughout the sleep period, and partly because they are most commonly prescribed without objective evidence regarding how much breathing support the patient needs as the disease progresses and the breathing muscles weaken further.