Physical Principles of Gas Exchange - Quiz 4 Flashcards
In what directions do gas move?
Randomly, both in and out through membranes and fluids of respiratory structure
What is the mechanism and rate of molecule transfer dependent on?
Gas Diffusion and Partial Pressure
Basis of Gas Diffusion
- Gas molecules free to move across membranes
- molecules not attached to one another
- Dissolve easily into fluids or tissues
What is the energy source for gas diffusion?
Kinetic Motion
- Gas molecules move in a line at high velocity, bumping into eachother
- Random movement
Net Diffusion of Gas
- When there is a concentration gradient, net diffusion of gas moves in one direction
- Rate of diffusion depends on pressure
Composition of Air
- 79% N; 21% O2
- 1 atm = 760 mmHg
Henry’s Law
Solubility of gas in a liquid depends on
Temperature
Partial Pressure of gas over liquid
Nature of Solvent
Nature of Gas
In water, ______ is 20x more soluble than ________
CO2 is 20x more soluble than O2
What is the Rate of Net Diffusion determined by?
Difference of Partial Pressures (pp)
- pp in alveoli > blood = gas moves into blood (oxygen)
- pp in blood > alveoli - gas moves to alveoli (co2)
What is the Vapor Pressure when gas mixture is fully humidified to 37 C?
47 mmHg
- VP depends on temp. Higher temp = higher kinetic energy and more water escaping into gas
Partial Pressure of Oyxgen in Upper Airway
713 mmHg * 21% = 150 mmHg
Factors that Affect Gas Diffusion Rates
Pressure Differences
Gas Solubility in Fluid
Area of Fluid
Distance for gas diffusion
Molecular Weight of Gas
Temperature of Fluid (constant in body)
D is __________ proportional with solubility and __________ proportional to the sq. root of the gas’ molecular weight.
Directly, Inversely
What are respiratory gases highly soluble in?
Lipids
What limits the rate of gas movement into tissues?
Diffusion rate of gas through tissue water
Movement of gas into/out of tissues = diffusion rate of gas through water
Why is Alveolar air different from Atmospheric Air?
- Alveolar air is partially replaced by atm. air with each breath.
- O2 constantly going to blood and CO2 to alveoli
- Air entering lung is humidified, diluting gas partial pressures
What concept prevents sudden changes in gas concentrations and allows respiratory stability?
The way alveolar air is renewed - multiple breaths needed to exchange alveolar air.
- 350 ml of air/breath
- FRC = 2500 mL
- Each breath replaces a seventh of FRC
- prevents sudden changes in gas concentrations
- allows more respiratory control
How long does it take for normal breathing to remove 1/2 of alveolar gas
17 Seconds
What is normal alveolar PO2
100 mmHg
What is normal alveolar PCO2?
40 mmHg
Alveolar PCO2 increases in proportion to CO2 excretion
When is Dead Space Air and Alveolar Air expired?
Dead Space Air expired in first portion and alveolar air is expired at end of exhalation
Factors that affect rate of gas diffusion through respiratory membrane
Thickness of Resp. Membrane
Surface area of Resp. Membrane
Coefficient (D)
Pressure Difference across Resp. Membrane
Rate of diffusion is ______ proportional to membrane thickness
Inversely
Increase in thickness by 2-3x significantly interferes
EX: Edema, Fibrosis
How does decreasing membrane surface area effect Diffusion Rate?
Decreasing surface area by 1/4 impedes gas significantly
EX: Removing Lung tissue or Emphysema (5x decrease)
How much faster does CO2 diffusion in relation to O2
CO2 diffuses 20x faster than O2
How much faster does O2 diffuse in relation to Nitrogen
O2 diffuses twice as fast as Nitrogen
What is Diffusion Capacity
Volume of gas that will diffuse through the resp. membrane each minute for a pressure difference of 1 mmHg
In what terms is the ability to exchange gas b/t alveoli and pulmonary blood expressed?
In Quantitative Terms
Factors that affect diffusion rate through resp. membrane also affect what?
Diffusion Capacity
What is the diffusion capacity for O2
21 mL/min/mmHg
What is the mean oxygen pressure difference across the resp. membrane
11 mmHg
How is the Total Quantity of O2 diffusing across membrane per minute calculated?
Total amt. of O2 diffusing = Pressure Difference X Diffusing Capacity
How is Diffusing Capacity effected by Exercise?
Increases 3-5x to Max (65 mm/min/mmHg)
d/t more recruitment and better V/Q
Resting Diffusing Capacity of CO2
400 mL/min/mmHg
Diffusing Capacity of CO2 with Exercise
1200 mL/min/mmHg
Carbon Monoxide Method for Measuring Diffusing Capacity
Used to calculate O2 Diffusion Capacity
- Measure alveolar CO pressure
- Multiply CO diffusing capacity by 1.23
What is the quantity of V/Q if there is perfusion, but no ventilation
V/Q = 0
What is the quantity of V/Q when there is ventilation, but no perfusion?
V/Q = Infinity
What is the PO2 and PCO2 in normal deoxygenated Blood?
PO2 = 40 mmHg
PCO2 = 45 mmHg
When is V/Q Below Normal
Shunt: Perfusion, no Ventilation
When is V/Q greater than Normal?
Dead Space: Ventilaton, no Perfusion
Diffusing Capacity of CO
17 mm/min/mmHg
