O2 and CO2 exchange Flashcards
Measure of ventilation
Respiratory minute volume = Tidal volume + Respiratory rate
Ve = Vt + f
Typical ventilation rate
6L/min
What is dead space?
The amount of space that air occupies in the respiratory system that do not contribute to GE
What is Dead space denoted by?
Vd and it is about 150ml
Alveolar ventilation rate equation
(Vt - Vd) x f
Why are tiny breaths not helpful?
The air may not reach the GE surfaces i.e the alveoli
Dalton’s law
- In a gas mixture (air), each gas exerts its own individual
pressure, called a partial pressure (P)
-The pressure of a mixture of gases = the sum total of the
pressures of each individual gas
What happens to the PP of O2 as it moves from Atm to the alveoli
Decreases due to diffusion
What does the air become saturated with as we breathe?
H2o vap
PP of O2 in the atm(tot)
160mmHg
Why do gases move across the membrane?
It is wet in the alveoli
- The gases have a tendency to dissolve in solution but they still have a PP
- Gases keep dissolving until the PP of O2 is at equilibrium
Fick’s law of diffusion
Gases move across the membranes
between the alveoli and the capillaries by diffusion
What determines the rate of diffusion?
- Surface area of the membranes
- Thickness of the membranes
- Pressure difference between the
two sides
Equation of Fick’s law
F = (A/T) x D x (P1-P2)
F = Flux (Amount flowing)
A = surface area
T = thickness
D = Diffusion constant
P1-P2 = pressure difference
What is D
Diffusion constant or coefficient for substance depends on gas solubility (S) and its molecular weight
Emphysema
disease characterized by dilation of the alveolar spaces and destruction of the alveolar walls
What is the main factor of GE
Pressure difference
PAO2 depends on
- Partial pressure of oxygen in
inspired air (almost negligible as most ppl are at sea level) - Alveolar ventilation (rate of breathing)
- Oxygen consumption – Blood
oxygen
What is O2 consumption in the body?
Our metabolism i.e how much O2 end up in our venous blood that drive the diffusion gradient of O2 in the lungs
PACO2 depends on
- Partial pressure of CO2 in
inspired air - Alveolar ventilation
- Carbon dioxide production
