Carseats and oxygen levels, a question!

[EmilyA874]

I've read the data about carseats lowering babies oxygen levels but was wondering if there was a difference in oxygen levels between different carseats? We were planning to skip the infant seat with baby #2 and get a RXT like we did for our DD, but baby boy has some health concerns that will effect his oxygen levels. Are infant seats better than a convertible in this regard or is there no real difference? Sorry if this is a silly question, I just have so little control in this situation I guess I am trying to control what I can. Any help is appreciated.