Gas Exchange, O₂/CO₂ Transport & V/Q Matching

By completing this question set, you will be able to apply Fick's law to predict when diffusion impairment causes hypoxemia and interpret DLCO changes in specific diseases (emphysema, fibrosis, anemia, pulmonary hemorrhage). You will calculate the A-a gradient from ABG data and use it to localize the cause of hypoxemia — distinguishing hypoventilation (normal A-a gradient) from V/Q mismatch, diffusion impairment, and shunt (elevated A-a gradient). You will classify hypoxemia into one of five mechanisms and predict whether supplemental O₂ will correct it — critically, identifying right-to-left shunt as the only cause that does NOT respond to 100% O₂. You will predict O₂-Hb dissociation curve shifts from physiologic and pathologic perturbations and trace their consequences for O₂ delivery, including the dual mechanisms by which CO poisoning and methemoglobinemia impair O₂ transport. You will describe the three forms of CO₂ transport, explain the Haldane effect and chloride shift, and integrate these with the Bohr effect to describe the complete O₂/CO₂ exchange cycle. Finally, you will apply V/Q concepts to explain regional differences in gas exchange, predict hypoxemia mechanisms in specific diseases, describe the West zone model, and trace the complete physiologic response to high altitude including acclimatization and altitude illness pathogenesis.