Session 7 Physical Principles of Gas Exchange Flashcards
Room air gasses and percentages
Oxygen 21%
Nitrogen 79%
What type of energy provides the source for the diffusion process
Kinetic Energy
Movement of gas in one direction is the effect of…
concentration gradient
Rate of diffusion is dependent on _________.
pressure
total pressure commonly used
1 atmosphere (weight of a column of air a mile high) 760 mmHg
The colder the liquid the ________ gas it can absorb.
more
Henry’s Law
solubility of a gas in a liquid depends on temperature, the partial pressure of the gas over the liquid, the nature of the solvent, and the nature of the gas.
Carbon dioxide is ____________more soluble than oxygen.
20 times
Rate of net diffusion os determined by
difference of partial pressures (pp)
If pp of gas in alveoli > blood then gas moves into ________.
blood
oxygen
If pp of gas in blood > alveoli then gas moves into
alveoli
Carbon Dioxide
Partial pressure of water escaping surface into gas phase = vapor pressure. Vapor pressure is _______ when a gas mixture is fully humidified at 37degrees C
47 mmHg
With vapor pressure considered, what is the remaining total pressure of gases in the air?
713 mmHg
760 mmHg - 47 mmHg (vapor pressure)
What factors affect gas diffusion rates in fluids?
Pressure differences Gas solubility in fluid area of fluid distance which gas must diffuse molecular weight of gas Temperature of fluid (constant in body)
D is directly proportional to
solubility
D is inversely proportional to
the square root of the gas’ molecular weight
Rate of gas movement into tissues is limited by diffusion rate of gas through _________.
tissue water
How much alveolar air is replaced per breath?
350 ml
FRC is roughly how many ml?
2500 ml
(Each breath replaces a seventh of the FRC
Normal Alveolar PO2 is
100 mmHg
Normal Alveolar PCO2 is
40 mmHg
What affects alveolar PO2?
rate of ventilation
oxygen pressure
exercise
Expired air is a combination of
Dead space
Alveolar air
Alveolar air is expired at _____________.
end exhalation
Overall thickness of respiratory membrane?
0.6 micrometers
Total surface area of respiratory membrane
70 square meters
Fick’s Law
Diff. = (A * change pp * D)/T
A is cross sectional area of membrane
change pp = the driving pressure (partial pressure difference
D is the gas coefficient
T is the tissue thickness or length through membrane
With regard to surface area, Emphysema causes the dissolution of many alveolar walls to coalesce alveoli into larger chambers. This can decrease surface area as much as __________. Does this increase or decrease the diffusion rate?
5 fold
decreases (r/t decreased surface area on which to diffuse)
CO2 diffuses _______ than oxygen.
20 times faster
Oxygen diffuses __________ as nitrogen
twice as fast
Diffusion Coefficient is affected by
Solubility
molecular weight
Diffusion capacity deals with
how easily a gas can move across a membrane in quantitative terms.
Oxygen diffusion capacity during exercise is increased r/t several factors:
Recruitment of capillary fields
Better ventilation/perfusion (V/Q) match (All Zone 3)
CO2 has ___________ concentration differences between blood and alveoli.
minimal very soluble difficult to measure CO2 diffusion capacity Alveoli - 40 mmHg Blood - 46 mmHg
When ventilation = zero but perfusion is present, what is the V/Q
Zero
blockage in airway
If ventilation present but no perfusion, then V/Q=
infinity
ex: pulmonary embolism
If V/Q is either zero or infinity, there is _______ exchange of gases
no exchange of gases
In normal deoxygenated blood, the PO2 is____ and the PCO2 is _____.
PO2 = 40 mmHg PCO2 = 45 mmHg
PP of gases in the Alveoli ___________ the PP of gases in the pulmonary vein
exactly match
100mmHg PaO2, 40 mmHg PaCO2
Shunt
perfusion without ventilation
V/Q is below normal
Shunt blood is/is not oxygenated?
is not oxygenated
Physiologic shunt is
total amount of shunted blood per minute
Physiologic dead space
V/Q is greater than normal Ventilation but no perfusion wasted ventilation anatomical dead space (ventilated air does not reach blood) has to do with embolism in pulmonary circulation
