Obviously, V T must be bigger than V D for effective gas exchange to take place. The symbols VA, VD, and VE are traditionally written with a dot over the V to signify that these are flows, that is, they represent values expressed in litres per minute. Partial Pressure Gases occupy a container at a particular pressure. In a gas mixture, we need to be able to express the relative amounts of each component. This is done in terms of the partial pressure of a component gas, which is the pressure the gas would exert on its own if all the other gases were suddenly removed from the container.
Gases exert partial pressures in proportion to their relative numbers of molecules.
The partial pressure of water vapor in a saturated gas at body temperature is 47 torr. The volume of CO 2 eliminated from the lungs each minute is the amount coming out with each expiration times the number of expirations per minute. This equation shows that alveolar PCO 2 is determined by the ratio of CO 2 production to alveolar ventilation. This is done by keeping minute ventilation high enough to maintain alveolar ventilation at a sufficient level. Hyperventilation is the opposite.