A model of fluctuating alveolar gas exchange during the respiratory cycle.

Abstract The effect of fluctuating alveolar gas concentrations and pulsatile blood flow on gas exchange between pulmonary capillary blood and alveolar gas is analyzed by means of a digital computer model. The model makes provision especially for: 1) variable partial pressure profiles in pulmonary capillary blood, 2) solubility of gases in pulmonary tissue, 3) pulsatile blood flow, and 4) the complex interrelationships of CO2, O2 and H+ in the blood. It is shown that fluctuating alveolar concentrations pulsatile blood flow and presence of lung tissue between alveolar gas and capillary blood all play an important role in the determination of instantaneous values of: 1) alveolar gas tensions, 2) oxygen uptake and carbon dioxide output, 3) gas exchange ratio of alveolar gas, 4) gas exchange ratio of pulmonary capillary blood and 5) gas tension profiles in the pulmonary blood. All of these values show large fluctuations during the normal respiratory cycle. These fluctuations are heavily dependent upon the pulmonary blood flow characteristics. The calculation of gas tension profiles in the pulmonary capillary is also discussed. The inclusion of the Bohr effect is shown to be very important. The variables are assessed for both normoxia and hypoxia.