While Greg’s use of a balloon is beneficial to model the effect of chest expansion on the establishment of positive air pressure (relative to atmospheric pressure), a balloon is not the chest wall- meaning there is intercostal (between the ribs) musculature which enables the expansion of the rib cage when those muscles are activated. If those muscles remain active/ contracted then the chest will remain expanded and no air will move either in or out. It is thus possible to have a lowered tongue and open throat (concert hall breath) and no air movement. Think about a breath attack… it is consciously controlled relaxation of the intercostal muscles with open throat and lowered tongue!