Glen,
First I hope I did not offend you as obviously I am still learning here and you must be doing well with your CPAP.
My Dad has bulbar onset ALS and his first symptoms were swallowing, speech and breath support problems so this is the perspective I was looking for when trying to help my Dad get the services he needs.
In regards to my Dad, probably the most useful info I received was from my friend who is a RT. She discussed that PALS have a difficult time with the exchange of gases (oxygen and carbon dioxide), especially in the supine position. She explained (as I understood it) that a CPAP machine will force the lungs to inflate with oxygen however weakened lung muscles can not force the carbon dioxide out back past the continuous pressure. The PALS has to work against the machine and could continue to retain carbon dioxide. She explained this could do more harm than good due to the stress of working against the machine.
The ALS Family Guide provided to my Dad by the ALS clinic actually states.. "It is important to use bipap and not CPAP. The bipap has 2 pressure settings, higher when you breathe in and lower pressure when you breathe out. These pressures can be set individually. CPAP just has high pressure. ALS patients can not tolerate CPAP. "
The information I read on the internet were similar to above. Here are a couple of links that are not medical by nature but were some of the information I absorbed.
"A CPAP (continuous positive airway pressure) machine is not indicated in ALS. CPAP increases the work of breathing by forcing the user to exhale against resistance. This can be dangerous for those with ALS"
http://www.als-mda.org/publications/everydaylifeals/ch5/
"People with ALS should not use CPAP (continuous positive airway pressure) machines because this increases the work of breathing out. CPAP is used to treat obstructive sleep apnea, rather than for neuromuscular disorders where "assisted ventilation" is needed."
http://www.alscareproject.org/respmgt/nasal-ventilation.pdf
"Continuous positive airway pressure also shouldn't be used for respiratory muscle weakness and hypoventilation. CPAP doesn't provide sufficient inspiratory assistance, and it increases the expiratory work of breathing. CPAP is useful for ALS patients with sleep apnea, without respiratory muscle weakness and hypoventilation."
http://www.alsindependence.com/Treating_Respitory_Problems_in_ALS.htm
The above information concerned me and prompted me to ask questions to make sure my Dad received the right help for him.
Dana