I think that there are about 12 or so of the infant lung function machines accross the US. Perhaps there are more now. Anyway, a young child (up to around 2.5 years) is sedated by an oral medication and is placed in a pressurized "box" for about an hour. They are able to place a mask over the face and force air into the lungs to determine the lung function. My son had it done a 6, 7, 13, 19 months old for the study I was referring to. The good news for my son is that it showed his lungs are functioning as well as a child his age without cf and he is not showing lung disease at this point.
Honestly, I would not jump to have my son retested. But he was having a lot of respiratory issues at six months when we decided to do the study, so it did help us decide what was going on with him. I think it was just a reflux related cough since it went away with Prevacid when he turned nine months old. Our cf center received the machine when my daughter (w/cf also) was one years old. I choose not for her to take the test since she does not have a lot of respiratory issues. That was a good decision for us. I have not enjoyed seeing my son put to sleep and watch the air forced into his lungs like that. But it did serve a purpose and I think it is important for us to participate in research.
Sharon, mom of Sophia, 3.5 and Jack, 19 months both with cf