Pulmonary Diffusion Flashcards
why does CO2 diffuse out of the capillary while O2 diffuses inwards?
they both are moving down their partial pressure gradients
what are the three components separating blood and air in alveoli?
alveolar epithelial cells, basement membrane and capillary endothelial cells
what does henry’s law state about gas solubility?
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
what is the partial pressure of the gas multiplied to get the gas content of a liquid?
the solubility coefficient
what determines the gas solubility coefficient?
the gas, the liquid it is dissolved i nand the temperature
how do the dry gas fraction and the partial pressure differ?
the dry gas fraction only is used for the gas phase but PP is used for both gas and liquid phase
what does fick’s law about partial pressures state?
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
what are the two equations for fick’s law?
flow of gas= DL(P1-P2)
DL= DA/T
D=diffusion coefficient
what is the diffusion of a gas proportional to?
solubility/ square root(molecular weight)
what is the diffusion coefficient of CO2 relative to O2?
it diffuses twenty times more rapidly than O2
what impact does the large diffusion coefficient of CO2 on hypoventilation and diffusion problems?
hypoventilation- hypercapnea and hypoxia
diffusion problem- only hypoxia
(the small amt of time is enough for CO2 diffusion
what is the normal transit time in the pulmonary capillaries?
0.75-1.2 sec at rest
describe the diffusion of nitrous oxide across the alveolar capillary membrane. how can it be increased?
it is very rapid
can be increased by increasing cardiac output and reducing amt of time the blood stays in capillary after equilibration
what type of limit is exhibited by O2 and N2O transfer into the blood?
perfusion limited
what type of limit is exhibited by CO? why is this the case?
diffusion limited uptake
true because hemoglobin is a CO sink and prevents equilibration of CO partial pressures
why is O2 equilibrated in the pulmonary capillary when CO is not and they both use hemoglobin as a carrier?
because there is a much larger amount of oxygen in the alveoli that is available for diffusion
why does CO2 take a while to diffuse out of the capillary, even though it has a very high diffusion coefficient relative to O2?
because it has to be made from bicarbonate in the blood, slowing the rate of equilibration
why is hypoxia due to poor diffusion demonstrated more readily in exercise than at rest?
because, while exercising, the transit time in the capillaries is severely reduced and the gas has less time to diffuse
why does altitude slow the rate of equilibration?
because the lower levels of oxygen cause hypoxic vasoconstriction in the lung
why is an individual with a diffusion problem be more hypoxemic at high altitudes?
becuase the end-capillary partial pressure of O2 will be lower than the alveolar partial pressure of oxygen
what gas is used to measure the diffusion capacity and at what amount? what is the DL O2 compared to that of CO?
CO at 0.1% for 30 sec
DL O2= 1.23 DL CO
what is the ventilation of CO equal to? what is assumed in using this?
ventilation of inspired CO- ventilation of expired CO
assumes that flow inspired equals flow expired
what is the partial pressure of CO in the blood?
zero (hemoglobin sink)
what is the equation for DL CO?
DL CO= ventilation CO/ Pa CO
ventilation found by subtracting expired from inspired
Pa CO is measured from end tidal sample
what 3 factors influence DL CO?
body position, exercise and lung disease
how does body position increase DL?
distension of pulmonary vasculature by increased volume increases the area available for diffusion
what two results of lung disease could decrease DL?
decreasing the pulmonary surface area and by increasing the diffusion distance (fluid or thickened alveolar membrane)
