[TOC] Diffusion = main method of gas movement in the distal small airways and of gas exchange in the alveoli
- Gas exchange is dependent on several factors
- Intact alveolar-capillary membrane
- Partial pressure of the gas diffusing between the two compartments
- Time that individual red blood cells spend in the capillary bed to allow for complete gas exchange at the interface
- The rate of oxygen binding to the hemoglobin molecule is nonlinear and increases with each individual oxygen molecule bound
- This maintains the maximal pressure gradient between the oxygen in the alveoli and the partial pressure of oxygen dissolved in plasma → very efficient transfer across alveolar-capillary membrane
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In a normal patient this time is 2-3x that which is required to completely upload oxygen, therefore, diffusion is rarely impaired