Douglas Bag 150 Litre Douglas bag system, is a piece of equipment used in physiology and exercise science to collect and measure the volume of exhaled air, particularly for the purpose of analysing respiratory gases such as oxygen (O2) and carbon dioxide (CO2). The bag is equipped with a valve system that allows the subject to breathe in ambient air (inhale) and then directs their exhaled breath into the bag during the collection phase for gas analysis.
