You did not give any details about your body habitus prior to surgery. It can happen in fairly large people with a protruding abdomen, that when they undergo an abdominoplasty and make the abdomen flat, the intra-abdominal contents are squeezed into a smaller space. This in turn pushes against the diaphragm, and thus limits expansion of the lower lung segments.
I lay my patients down in the supine position on my examination table and examine them that way as well. If their abdomen does not go flat, I tell them that they are not an ideal candidate for a tummy tuck. If I would tighten their abdominal wall to make it flat (sometimes this is not possible), they would end up with the symptoms you are experiencing. For this type of patient, I recommend weight loss with diet and excersise program prior to surgery or if they are morbidly obese, lap band or gastric bypass prior to an abdominoplasty.
