Gas Exchange: Lecture 8 Flashcards
Where does gas exchange occur?
- lungs
- peripheral tissues
True or False
O2 and CO2 follow partial pressure gradients
True
What are 3 additional factors that affect the rate of gas transfer?
- As surface area increases, the rate increases
- bigger breather recruits more alveoli - Increased thickness in the barrier or air and blood will decrease the rate
- The rate of gas exchange is directly proportional to the diffusion coefficient of the gas
What is the equation for partial pressure?
Pp = Total pressure x gas fraction
In the lung, the total pressure is equalled to what?
atmospheric pressure (Patm)
Diffusion is passive therefore it travels from where to where?
High to low
In the lung, the “‘total pressure” will equal what?
atmospheric pressure (Patm)
True or False
Is the gas concentration of oxygen in this room the same as in Everest?
True, but the partial pressure will drop
Atmospheric air is composed of three elements which are what?
- Nitrogen
- Oxygen
- Carbon dioxide
What is the percentage of Nitrogen?
79.04%
What is the percentage of Oxygen?
20.93%
What is the percentage of Carbon dioxide?
0.03%
What is the Atmospheric pressure at sea level?
760
True or False
As the altitude goes up, the atmospheric pressure goes down and therefore the the partial pressure will go down
True
In a scenario where we are in a plane and there is a loss of cabin pressure, our PO2 will be very low how do we get it back up?
By using the oxygen tanks which are almost 100 percent oxygen, therefore we change the oxygen fraction from 0.2093 to something else
True or False
If we want to increase the PO2 at a high altitude we would need to increase the fraction
True
When we breathe out, what are the percentages of Nitrogen, Oxygen and Carbon dioxide?
Nitrogen = 79.95%
Oxygen = 15.85%
Carbon dioxide = 4.2%
Are expired air fractions different based on the person?
100% (yes)
What is the set point we want to keep our arterial CO2 at?
36-40 millimeters of mercury
What 2 factors help to facilitate diffusion?
- Pressure differences in alveoli
- Capillaries
True or False
Partial pressures drive the diffusion of oxygen going into the blood and carbon dioxide getting removed from the blood
True
What is Henry’s law?
The volume of gas dissolved in a liquid is proportional to the partial pressure of the gas
what does “C gas” equal?
concentration of gas in a liquid (ml/dl)
What does “k” equal?
solubility coefficient of the gas in the liquid
A higher k value means what?
less pressure is required to dissolve gas
What is the formula for Henry’s Law?
C gas = P gas x k
True or False
O2 and CO2 have different solubility coefficients
True
What is PaO2?
arterial partial pressure of O2
What is PAO2?
alveolar partial pressure of O2
What is the PVO2?
venous partial pressure of O2
In the atmospheric air, the PO2 is what?
160
When the oxygen gets to the alveoli what is the PO2 at now?
100
When the oxygen gets to the venous what is the PO2 at now?
40
True or False
Generally, the arterial PaO2 and the alveolar PAO2 in a perfect lung are the same
True, meaning that there is not any leakage in the interstitial space
What is an example where the PaO2 and the PAO2 are not equal?
Any interstitial lung disease, where you get a widening of that interstitial space
- pulmonary fibrosis
- cystic fibrosis
Is there ever a 0 PO2?
naurr
What is the PCO2 in the tissues?
greater than 46
What is the PVCO2?
about 46 or higher
What is the PCO2 when we expire?
40
What is the PACO2 and the PaCO2?
40
In a scenario where we are not breathing enough what is happening?
the build-up of CO2, can’t breathe out the CO2
What is hypercapnia?
- build-up of CO2
- lack of O2
What is hyperventilation?
- where we increase our ventilation relative to the production of CO2
What happens to your PCO2 and your PaCO2 during hyperventilation?
decrease
What happens to our PaO2?
increased
What is hypoventilation?
- under ventilating, not breathing enough
What happens to our PCO2 during hypoventilation?
increases
What are the 4 factors that can affect the alveolar pressure of oxygen PAO2?
- Decreased PO2 in inspiration (high altitude)
= decreased - Increased alveolar ventilation and unchanged metabolism
= increased - Increased metabolism and unchanged alveolar ventilation
= decreased - Exercise, equal metabolism and VA
= No change
What are the 4 factors that can affect the alveolar pressure of oxygen PACO2?
- Decreased PO2 in inspiration (high altitude)
= No change - Increased alveolar ventilation and unchanged metabolism
= decreased - Increased metabolism and unchanged alveolar ventilation
= increased - Exercise, equal metabolism and VA
= No change
What is ventilation-perfusion matching?
matching of the airflow to the alveoli and the blood flow to the capillary or the tissue
What is perfusion defined as?
blood flow to a tissue or an organ
What is a shunt?
when there is no ventilation to provide the blood with oxygen and therefore it remains deoxygenated and then gets pumped back into the left heart into circulation
If we have too many shunts taking place what will happen to our arterial PO2?
decrease
What is the normal ventilation to capillary perfusion rate?
1/1 or V/Q
What would the V/Q ratio look like in a shunt?
0/1
What is alveolar/pure dead space
when there is no blood flow but there is ventilation
- no capillary perfusion, for whatever reason
- therefore ventilation goes down to take place in gas exchange with the capillaries but there is no blood available so gas exchange does not occur
What does the V/Q ratio look like for alveolar/pure dead space?
1/0
The shunt will cause high or low PO2?
low
How do we counteract mismatched blood flow?
reflex hypoxic vasoconstriction of pulmonary arterioles
what does hypoxic vasoconstriction do?
helps to maintain highly efficient and effective gas exchange
what is hypoxic vasoconstriction
a reflex that helps minimize the areas of low ventilation-perfusion ratio
In which disease can we lose out on hypoxic pulmonary vasoconstriction
emphysema
What are 2 ways we increase perfusion throughout the lung
- lying down
- exercise
True or False
In emphysema, the surface area for gas exchange is decreased
True
What happens to your arterial PO2 in the case of exercising with ILD or pulmonary edema?
PO2 will drop
