Composition of Alveolar Gases | ||
Under normal breathing conditions the composition of alveolar gases is largely determined by two processes. | ||
1 |
Ventilation: the periodic partial replacement of alveolar air with fresh ambient air during inspiration. | |
2 |
Blood flow: CO2 diffuses out of the blood as it passes through the pulmonary capillaries while O2 from the alveoli diffuses into the blood stream from the alveoli. |
The tidal volume is around 500ml. This volume is added to the 2500ml of the Functional Residual Capacity (FRC) with every inspiration. As a result, there is a minimal variation (~17%) in the concentration of the gas mixture with every inspiration. Thus the FRC acts as a buffer against rapid and drastic changes in the alveolar air composition.