Totraum (engl. dead space): The dead space is the part of the breathing apparatus that does not take part in the gas exchange. There are three types of dead space: i) Anatomical dead space, i.e. nose, oral cavity, pharynx, trachea and bronchi, in which 30% of the inhaled air remains during inhalation. In the anatomical dead space the inhaled air is brought to body temperature, humidified, and filtered. ii) Alveolar dead space, i.e. those alveoli that due to an insufficient blood circulation or disease do not participate in the gas exchange. iii) Functional dead space which is the total volume of the anatomical and alveolar dead space. In healthy individuals the functional dead space is almost equal to the anatomical dead space. The dead space volume is calculated based on the Bohr equation.