The residual volume increases in diseases that trap air in the chest, such as emphysema. Excess residual volume decreases the efficiency of gas exchange. Another volume is the respiratory dead space, the amount of air within the chest that is not in contact with alveolar membranes and cannot exchange gases with the blood. The dead space becomes important in certain lung diseases, causing elevation of carbon dioxide levels. Respiratory dead space is NOT the same thing as residual volume.
Residual volume includes the respiratory dead space, plus whatever volume is left in the alveoli.
The vital capacity is often measured clinically. It s the maximum amount of air that the patient can expire after a full breath the sum of tidal volume, inspiratory reserve volume, and expiratory reserve volume. Peak expiratory flow is a measure of the maximum speed of expiration in volume of gas per second. Back to Index. For purposes of blood gas analysis, the amount of a gas present is expressed in terms of partial pressure.