After the end of a normal inspiration, the volume of air in the lungs is about 2.8 l. normally quiet inspiration is driven by a pressure difference of about 2 mm hg. the air in the lungs is at 37 ° c and after normal expiration it is at atmospheric pressure. quiet inspiration is driven by the expansion of the chest cavity by contraction of the diaphragm, which expands the air in the lungs. how much is the air feher, joseph j. quantitative human physiology: an introduction (academic press series in biomedical engineering) (kindle locations 3177-3180). elsevier science. kindle edition.