Pulmonary Diffusion

Question 1

why does CO2 diffuse out of the capillary while O2 diffuses inwards?

Answer 1

they both are moving down their partial pressure gradients

Question 2

what are the three components separating blood and air in alveoli?

Answer 2

alveolar epithelial cells, basement membrane and capillary endothelial cells

Question 3

what does henry’s law state about gas solubility?

Answer 3

when a liquid and gas phase are in equilibrium at a given temperature, the concentration of gas in solution is directly proportional to the partial pressure of the gas

Question 4

what is the partial pressure of the gas multiplied to get the gas content of a liquid?

Answer 4

the solubility coefficient

Question 5

what determines the gas solubility coefficient?

Answer 5

the gas, the liquid it is dissolved i nand the temperature

Question 6

how do the dry gas fraction and the partial pressure differ?

Answer 6

the dry gas fraction only is used for the gas phase but PP is used for both gas and liquid phase

Question 7

what does fick’s law about partial pressures state?

Answer 7

that the flow of gas across the membrane is directly proportional to the area of the membrane and partial pressure differences of the gas. it is inversely proportional to the thickness of the membrane

Question 8

what are the two equations for fick’s law?

Answer 8

flow of gas= DL(P1-P2)
DL= DA/T
D=diffusion coefficient

Question 9

what is the diffusion of a gas proportional to?

Answer 9

solubility/ square root(molecular weight)

Question 10

what is the diffusion coefficient of CO2 relative to O2?

Answer 10

it diffuses twenty times more rapidly than O2

Question 11

what impact does the large diffusion coefficient of CO2 on hypoventilation and diffusion problems?

Answer 11

hypoventilation- hypercapnea and hypoxia
diffusion problem- only hypoxia
(the small amt of time is enough for CO2 diffusion

Question 12

what is the normal transit time in the pulmonary capillaries?

Answer 12

0.75-1.2 sec at rest

Question 13

describe the diffusion of nitrous oxide across the alveolar capillary membrane. how can it be increased?

Answer 13

it is very rapid

can be increased by increasing cardiac output and reducing amt of time the blood stays in capillary after equilibration

Question 14

what type of limit is exhibited by O2 and N2O transfer into the blood?

Answer 14

perfusion limited

Question 15

what type of limit is exhibited by CO? why is this the case?

Answer 15

diffusion limited uptake

true because hemoglobin is a CO sink and prevents equilibration of CO partial pressures

Question 16

why is O2 equilibrated in the pulmonary capillary when CO is not and they both use hemoglobin as a carrier?

Answer 16

because there is a much larger amount of oxygen in the alveoli that is available for diffusion

Question 17

why does CO2 take a while to diffuse out of the capillary, even though it has a very high diffusion coefficient relative to O2?

Answer 17

because it has to be made from bicarbonate in the blood, slowing the rate of equilibration

Question 18

why is hypoxia due to poor diffusion demonstrated more readily in exercise than at rest?

Answer 18

because, while exercising, the transit time in the capillaries is severely reduced and the gas has less time to diffuse

Question 19

why does altitude slow the rate of equilibration?

Answer 19

because the lower levels of oxygen cause hypoxic vasoconstriction in the lung

Question 20

why is an individual with a diffusion problem be more hypoxemic at high altitudes?

Answer 20

becuase the end-capillary partial pressure of O2 will be lower than the alveolar partial pressure of oxygen

Question 21

what gas is used to measure the diffusion capacity and at what amount? what is the DL O2 compared to that of CO?

Answer 21

CO at 0.1% for 30 sec

DL O2= 1.23 DL CO

Question 22

what is the ventilation of CO equal to? what is assumed in using this?

Answer 22

ventilation of inspired CO- ventilation of expired CO

assumes that flow inspired equals flow expired

Question 23

what is the partial pressure of CO in the blood?

Answer 23

zero (hemoglobin sink)

Question 24

what is the equation for DL CO?

Answer 24

DL CO= ventilation CO/ Pa CO
ventilation found by subtracting expired from inspired
Pa CO is measured from end tidal sample

Question 25

what 3 factors influence DL CO?

Answer 25

body position, exercise and lung disease

Question 26

how does body position increase DL?

Answer 26

distension of pulmonary vasculature by increased volume increases the area available for diffusion

Question 27

what two results of lung disease could decrease DL?

Answer 27

decreasing the pulmonary surface area and by increasing the diffusion distance (fluid or thickened alveolar membrane)