Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. In physiology, dead space is air that is inhaled by the body in breathing, but does not take part in gas exchange. Not all the air in each breath is able to be used for the exchange of oxygen and carbon dioxide. About a third of every resting breath has no change in O2 and CO2 levels. In adults, it is usually in the range of 150 mL. Because of dead space, taking deep breaths more slowly (e.g. ten 500 mL breaths per minute) is more effective than taking shallow breaths quickly (e.g. twenty 250 mL breaths per minute).