Quantification of pulmonary gas exchange: Combined effects of gas solubility and transport mechanisms

The primary function of the lungs is to exchange the respiratory gases, O₂ and CO₂, between the atmosphere and the blood. However, other gases are known to exchange in the lungs depending on their solubility in blood. Solubility of gas in blood can be quantified by the blood:air partition coefficient, λ_b:a. Low blood-soluble gases (λ _b:a < 10) such as O₂ and CO₂ exchange the alveoli and high blood-soluble gases (λ_b:a > 1000) such as ethanol exchange in the airways. Intermediate blood-soluble gases (e.g., pollutant and anesthetic gases) are thought to exchange in the airways and alveoli, but the exact location is unknown. For medical and legal purposes, it is important to determine where these intermediate blood soluble gases interact with the lung.; The primary goal of this dissertation was twofold: (1) develop and validate a mathematical model that simultaneously predicts airway and alveolar gas exchange; and (2) using this model, determine where gas exchange occurs (airways or alveoli) as a function of λ_b:a. First, anatomical data on the bronchial circulation were collected and incorporated into an existing airway gas exchange model to accurately represent of the diffusion and perfusion dependence to airway gas exchange. Second, this airway gas exchange model was expanded to include a time dependent description of alveolar gas exchange. Third, the resulting airway-alveolar gas exchange model was validated with two sets of experimental data. Fourth, the validated airway-alveolar model simulated the exchange of gases with 0.01 < λ_b:a < 1000 to determine the location of gas exchange as a function of λ _b:a. It was found that gases with 1 < λ_b:a < 100 exchange partially in the airways and partially in the alveoli while gases with λ_b:a > 100 and λ_b:a < 1 exchange completely in the airways and alveoli, respectively.; The secondary goal of this dissertation was to determine the effects of airway gas exchange on whole organ gas exchange in sheep using a novel experimental technique. Since airway gas exchange has been shown to be dependent on bronchial blood flow, the experiments were designed to alter bronchial blood flow and examine gas exchange measurements. It was found that end-expired gas concentrations of gases with 0.09 < λ_b:a < 300 were significantly affected by changes in bronchial blood flow.