What do the numbers mean?

We just recently had a follow up for my mom diagnosed fall of 2010. At that time her breathing was at 78% and now 5 months later it is at 71%. The dr did not seem overly concerned with these numbers, at what point (or number or percentage) is it a cause for concern? There has been definate weakness in her hands but her legs are still quite strong (Hooray for small things right?), altho she is scared to walk because of the falling. Her speech is slurred at times (def moreso when tired) but chewing and swallowing are fine, I thot it all went together? The most horrible part of the disease, dont get me wrong the whole disease is a horrible monster, is the not knowing what will be next. On a positive note, calculating by onset of symptoms, falling, muscle twitching, muscle spasms, in 2008, the dr does figure she has come close to passing the 3 year mark!

Usually when she gets to 50 they become more concerned. I know they like to do peg tube placement before that point and then they will also suggest a bi-pap. I already have both at 78%, but I also am chocking on some liquids and food and laying down my numbers went from 90 to 48%. Hope this helps.