The problem with the medical understanding of corsetry in the Victorian era is that it was based first on the assumption that corsets did this, that, and the other thing, and second on observation. The famous illustrations of corseted bodies vs. uncorseted bodies, showing the skeleton and organs being moved and displaced? These aren't documents of anatomical dissections that really occurred (not that it's even possible to dissect a body while it's wearing a tightly-laced corset), but what male doctors believed was happening to the body. Nobody actually knew from observation what the inside of a tight-lacer's body looked like until burlesque artist Eden Berlin had an MRI done while wearing a 20" corset (and please note, in terms of overall ratio of bust to waist to hips, this is more extreme on her than what would be seen in the fashionable tight-lacer of the Victorian period; while 20" waists are very common in historic clothing collections, they typically go along with a very slender figure overall) - and the results were underwhelming. The bottoms of the lungs were pushed up, a little of the intestines came up as well, and everything else largely stayed in place. For the most part, what corsets moved (and move) around was the fat of the waist, stomach, and hips.

The ribcage was certainly reshaped, but Rebecca Gibson's research (which I read as her doctoral dissertation, and which is due to be published this fall) has shown that the reshaping largely led to the ribs being molded into a circle, rather than the natural flattened oval. We don't typically see this in modern corset-wearers because today, children and teenage girls don't use them regularly while their bones are still malleable; for modern adult women, the bones are generally set and don't reshape like this, the same way that braces are much more effective on teenagers than adults. Gibson determined that this had likely no effect on overall health at all, and that women had no issues going through pregnancy with their bodies having been shaped this way. For more on how Victorian women dealt with pregnancy and corsets, I have a previously-written answer here.