Pulmonary Diffusion and Gas Exchange Flashcards
What affect does breathing 100% oxygen have on the PACO2?
It remains unchanged
What is alveolar ventilation?
Volume of fresh air entering alveoli per minute
What does gas exchange require?
Diffusion of gas
Perfusion of blood
What is Fick’s Law?
Rate of diffusion across a tissue barrier is proportional to the surface area, diffusion constant, pressure gradient and inversely proportional to tissue thickness
What is Graham’s Law?
When gases are dissolved in liquids, the rate of diffusion is inversely proportional to the square root of the gas density i.e. gas with a lower molecular weight will diffuse faster
Is oxygen or carbon dioxide more soluble?
CO2 by 22 degrees
What is Henry’s Law?
Correlation between solubility of gas in a liquid and its partial pressure
What is the rate of oxygen diffusion dependent on?
Integrated mean PO2 difference between alveoli and pulmonary capillary blood
What is the integrated mean PO2 difference between alveoli and pulmonary capillary blood dependent on?
Fractional intake of oxygen (FI)
Alveolar ventilation
Oxygenation of haemoglobin
Pulmonary capillary blood flow
What is the barometric pressure at sea level?
760mmHg
Define Dalton’s Law of Partial Pressure.
Each gas in a mixture of gases exerts a pressure according to its concentration and independent of other gases present
What is the fraction of air taken in the trachea?
0.21
What is the PH2O in the trachea?
47mmHg
What is the PO2 in the trachea?
150mmHg
What is the respiratory quotient dependent on in the alveolar gas equation?
Diet
CO2 produced
O2 consumed
What does air leaving alveoli mix with?
Dead space air
Air in trachea
What does the mixing of air leaving the alveoli do to the expired air?
Reduces its PCO2 compared to the alveoli
Increases its PCO2
Does partial pressure or gas concentration that comes to equilibrium during gas exchange?
Partial pressures
How long does it take blood to transverse pulmonary capillaries?
~0.75 seconds
How long does it take oxygen to equilibrate in the pulmonary capillaries?
~0.3 seconds
How long does it take carbon dioxide to equilibrate in the pulmonary capillaries?
Almost instantaneous
How much oxygen is dissolved in plasma?
1.5%
What is the primary PaO2 sensor?
Carotid body
Where is the PaCO2 sensed?
CNS
What does the transport of CO2 and O2 depend on?
Cellular metabolic rate