It is more likely that large sauropods possessed an adaptation in their soft tissues whose existence we can only guess at. As far as I know, paleontologists still maintain the Brachiosaurs held their necks erect. Given the skeletal remains, this appears to be the best way to reconstruct the animal. In this sense, the Brachiosaurs resembled giraffes. Hence, the problems giraffes face are magnified for the Brachiosaurs.
Giraffes reduce the dead air space in their windpipes through tracheal stenosis.
There are pneumatic ducts and cavities, including large pleurocoels, in the back and neck of all the sauropods. The Brachiosaurs also exhibited extensive pneumatic openings in the ribs. It does not seem unreasonable to speculate that the same thing was true of Brachiosaurs. The whole skeleton of these animals appears to be designed to save weight. If gravity were greatly reduced we would not expect to see such excavations in the bones.