I'm not really sure how cpap can directly help with weight gain. However there is some science to cf that might explain the thinking of the doctor.
When lungs are working really hard they use a lot of energy. To help get oxygen around the body the heart has to beat faster and harder aswell. Many people with cf have an enlarged heart because of this. An infection and mucus clearing also take a huge toll in the body which has to start making extra white blood cells to fight infection. So, while all this is happening there is a lot more energy being used. This can effect the amount of fat that is stored as it is being used straight away by the body. My thinking is cpap while helping the lungs and giving them a bit more of a break at night this might mean your sons body has to use less energy to breathe. This could indirectly effect weight gain I suppose.
That's just guess work, I may be wrong.
As for the breathing faster, this could be like the heart thing, the lungs are working harder to make sure it's getting as much oxygen as it can for your sons developing and growing body. Hopefully this will settle down when your sons body doesn't have to work so hard at night. Make sure you're writing down all your concerns and bringing them up with the doctor. It makes it a bit easier when you see the doctor if you have a list and don't have to remember everything.
Moderator of the Cystic Fibrosis forum
Hey, I'm Gem with CF, age 29 and diagnosed at 2 years old. I'm no expert but having CF myself I've learnt a few things along the way.
Diagnosed with: Cystic Fibrosis, Asthma, ABPA, Clinical Depression, Mild Liver Cirrohsis, Mild Osteopenia, Erythema Nodosum, Proximal Myositis, Polyarthralgia