lecture 18 - O2 and CO2 exchange Flashcards
What is the equation for respiratory minute volume?
VE = VT x f (VT=tidal volume, f=respiratory rate)
What is the symbol and unit for respiratory minute volume?
VE, L/min
What is the symbol and unit for tidal volume?
VT, L/breath
What is the symbol and unit for respiratory rate?
f, breaths/min
What is the ‘dead space’ of the lungs?
The air that does not reach the alveoli for gas exchange during a breath and fills the upper airways .
What is the approx. volume of dead space in the lungs?
150mL
What is the measure of how much air reaches the alveoli for gas exchange?
Alveolar ventilation, VA in L/min
What is the symbol and unit for alveolar ventilation?
VA, L/min
What is the equation for alveolar ventilation?
VA=(VT-VD)*f (VT=tidal volume, VD=dead space, f=respiratory rate)
What is the symbol and unit for dead space?
VD, L/breath
What is the difference between tidal volume (VT), dead space (VD) and alveolar ventilation (VA)?
VT is the total volume that enters the lungs in each breath, VD is the volume that sits in the upper airways and does not reach the lungs, and VA is the total volume that reaches the alveoli. The difference between VT and VA is VD
What does gas diffusion depend on?
The partial pressures of gases in the airway and exchange pathway
What is Dalton’s Law?
States that in a gas mixture, i.e. air, each gas exerts its own individual partial pressure (P). The pressure of the mixed gas is the sum total of the partial pressures of each individual gas.
What is atmospheric pressure, in mmHg?
760mmHg
What is the goal of the blood air barrier?
To facilitate the transport of inhaled oxygen into the capillaries and transport carbon dioxide into the alveoli to be exhaled
What is the principle of Fick’s Law of Diffusion?
Gases move across membrane between alveoli and capillaries by diffusion, which depends on surface area and thickness of the membrane, as well as the pressure difference of gases
What is the equation for Flux (amount of gas flowing) according to Fick’s Law of diffusion?
F=A/T * D(P1-P2), (A=surface area, T=thickness, D=diffusion constant, P1-P2 = pressure difference)
What is the symbol for the diffusion constant?
D
What is the diffusion constant, according to Fick’s LAw of Diffusion?
A constant (D) that depends of the gas solubility and molecular weight of a gas, such as O2 or CO2
Why does CO2 diffuse around 20x faste than O2?
CO2 is more soluble so has a greater diffusion constant, D
What is emphysema, and how does it influence gas exchange?
Disease characterised by dilation of alveolar walls, reducing the surface area for gas exchange
What is pulmonary fibrosis, and how does it influence gas exchange?
Thickening and scarring of the thin alveolar membranes, which increases the thickness that gases must diffuse through, limiting exchange
What is the main factor that drives movement of gases across the alveolar and capillary membranes?
Difference between the partial pressures of O2 and CO2 in the alveoli and arteries (PAO2 vs PaO2 and PACO2 and PaCO2)
What is the symbol for alveolar partial pressure of O2?
PAO2
What is the symbol for alveolar partial pressure of CO2?
PACO2
What does the gas pressure difference between alveoli and capillaries depend?
1.) partial pressure of gas in inspired air (though this is relatively constant, and negligible for CO2)
2.) alveolar ventilation (amount of air)
3.) blood gas level (oxygen consumption or carbon dioxide production)
How does exercise or rest influence partial pressure of oxygen in the blood?
Exercise increases oxygen consumption so lowers pressure, while rest does the opposite
How do gases move along a pressure gradient?
Move down a pressure gradient, from high partial pressure to low partial pressure
