diffusion

Question 1

Respiratory unit

Answer 1

Composed of respiratory bronchiole, alveolar duct, atria, and alveoli

300 million alveoli in 2 lungs
Average diameter of each alveolus

Question 2

Alveolar walls and vascular supply

Answer 2

extremely thin alveolar walls
Solid network of interconnecting capillaries
Gas exchange occurs thru the membranes of all terminal portions of lungs, respiratory/pulmonary membrane

Question 3

Diffusion

Answer 3

transfer of gas across the blood-gas barrier, described by FICks law, rate of trasnfer of a gas thru a sheet of tissue

Directly proportional to tissue area, the difference in gas partial pressure between the 2 sides and the diffusion property of the gas, inversely proportional to the tissue thickness

Question 4

Ficks law

Answer 4

Volume of gas propotional to (pressure gradient x surface area)/distance

Volume of gas proportional to solubility/square root molecular weight

Question 5

REspiratory membrane

Answer 5

as little as .2 um, averages .6 um, total surface area – 70 sq m
Total amount of blood in pulmonary capillaries- 60-140 mL
Average diameter of pulm capillaties- 5um
Average diameter of RBC-6um

Surface area, thickness, pressure graddient affects diffusing capacity of a gas

Question 6

Diffusing capacity

Answer 6

Rapid inhalation of a diffusion gas mixture to TLC (from spirometry/demand valve/reservoir)

.3% CO, 10% HE, 21% O2, Balance nitrogen

Question 7

Adequacy of the effort

Answer 7

The volume inspired (VI) should be >90% of the largest vital capacity (VC) to show that any reduction in VA is not due to poor inspiratory effort

A maneuver may also be considered acceptable if the VI is within 85% of the largest VS and teh VI is within 200 mL or 5 %,

Question 8

diffusing capacity of respiratory membrane

Answer 8

defined as the volume of a gas that will diffuse thru the membrane each minute for a partial pressure difference of 1 mmHG
Average young man- diffusing capacity for Oxygen under resting conditions averages 21 mL/min/mmHg
Mean oxygen pressure difference across the respiratory membrane under normal resting condition -11 mmHg

230 mL of O2 diffuses thru the respiratory membrane each minute

Question 9

Pulmonary function testing

Answer 9

Spirometry/FV loop

Lung volumes, diffusing capacity