This chapter focuses on the mechanisms of gas exchange between lungs and environment. In particular, it describes the changes in gas composition and physical property that take place as gases are flown in and out of the lungs. It explains the meaning of anatomical (conductive) dead space and describes methods for quantifying dead space, alveolar ventilation, oxygen consumption and carbon dioxide production. It introduces concepts of ideal versus average alveolar ventilation, alveolar dead space ventilation, right-to-left blood shunt (venous admixture), and body gas stores. It begins to explain how the complex relationship between alveolar ventilation and blood perfusion can be simplified into a “three compartment model” of the real lung. Finally, the relationship among alveolar ventilation, arterial PCO2 and metabolic rate is discussed and presented quantitatively.
Keywords: Alveolar Dead-Space, Alveolar Gas-Equation, Alveolar-Ideal Gas, Ambient-Temperature-Pressure-Saturated (ATPS), Blood Shunt, Body Gas-Stores, Body-Temperature-Pressure-Saturated (BTPS), Carbon-Dioxide Production, Conductive Dead-Space, Exchange Ratio (R), Expiration, Gas Composition, Inspiration, O2-CO2 Diagram, Oxygen Consumption, Physiological Dead-Space, Respiratory Quotient (RQ), Standard-Temperature-Pressure-Dry (STPD), Steady-State Condition, Ventilation-PCO2-Metabolism.