Unit 5.3 - Partial Pressure and Diffusion

Air Movement

Within a given volume of air moving across a section of tubing, velocity of flow is 1/cross-sectional area.

With a huge increase in cross-sectional area within the respiratory zone, there is a drastic decrease in relative velocity of flow.

When relative air velocity is approaching 0, the main mechanism for transport is diffusion.

Diffusion

The dominant mechanism for ventilation in the respiratory zone.

Rate of diffusion influenced by: partial pressure, solubility, and diffusivity.

Partial Pressure (Dalton’s Law)

The part of the total pressure generated from each gas type.

Determined by the percentage of volume represented by each gas type.

Solubility (Henry’s Law)

Concentration of gas dissolved in a liquid is proportional to its partial pressure.

Diffusivity (Fick’s Law)

rate of transfer = D*(area/thickness)*(difference in partial pressure)