Respiratory 2 Flashcards
Ventilation to perfusion ratio
- Ventilation is how many mL of air per minute are going in and out of the lungs
- Perfusion is how many mL of blood per minute are going to the lungs
- There can be variations in perfusion in different regions of the lungs
- Ideally, the V/Q ratio is constant, close to 1
What is ventilation?
How many mL of air per minute are going in and out of the lungs
What is perfusion?
How many mL of blood per minute are going to the lungs
How would ventilation to perfusion ratio be affected if there was something blocking a bronchus, and the other lung had an embolus blocking the pulmonary artery?
- There would be no ventilation in that lung with a blockage, only in the other
- There would be no perfusion to the lung with an embolus, only to the other
- So the V/Q ratio would be inefficient
Ventilation/perfusion ratio in lung (rest vs. exercise)
Watch lecture at 8:18
What is the capacitance of the lungs and what forces determine it?
- Capacitance is generally pretty high (not that hard to inflate), but some forces make it stiff)
- Change in pressure for a given change in volume determines capacitance
How does elastin affect the capacitance of the lungs?
Elastic fibers across the lungs cause the lungs to collapse at normal lung volumes, thereby decreasing capacitance
How does surface tension affect the capacitance of the lungs?
- The layer of water molecules on the inner side of alveoli are attracted to each other creating a force that tends to collapse these small spheres of air.
- This tendency for alveoli to collapse due to surface tension decreases capacitance of the lungs.
What is the function of surfactant?
Decreases surface tension of alveoli thereby increasing capacitance.
What is partial pressure?
The concentration of gas dissolved in a liquid or of gas molecules in the air
If the total atmospheric pressure is 760 mmHg, and the fraction of oxygen is 21%, what is the partial pressure of oxygen in air?
21% of 760 = 160 mmHg
This is when the air is dry (no water vapor)
What is the partial pressure of oxygen air going into the alevoli?
- As the air goes down the dead space, it picks up water vapor, so water molecules take the place of all the other molecules
- So PO2 = 0.21(760-PH2O)
= 760-47
=150 mmHg
How would a higher altitude, with a lower PO2 affect your ability to get oxygen into your lungs?
The lower partial pressure of oxygen makes it more challenging to get into tissues
Is oxygen soluble in water?
Not very
Why do we need to get oxygen molecules to dissolve into water?
They’ve got to go into the lining of the alveoli, through the alveoli, into the bloodstream, into the plasma, into a red blood cell, and then find a hemoglobin molecule
How do we overcome the low solubility of oxygen in water?
Hemoglobin molecules take up oxygen from the blood plasma and carry it bound, not in solution
What is the pressure of oxygen in water if there are only 2 molecules in it? (Watch lecture at 31:10)
PO2 would be 150 because it’s so desperate to escape so it exerts such a high pressure as it tries to escape from the water
Solubility of oxygen vs. carbon dioxide
CO2 is much more soluble in water (20x more CO2 than O2 can dissolve in water)
What is the significance of the solubility of O2 and CO2 in water?
Looking at the partial pressure of oxygen or CO2 in blood is only measuring the oxygen and CO2 that’s dissolved in solution (plasma or the fluid inside of red blood cells)
Is most of the oxygen and CO2 carried in solution?
No
What is PO2 and PCO2 in arterial blood?
PO2 = 100 mmHg
PCO2 = 40 mmHg
(This only shows what’s dissolved in solution)
What is PO2 and PCO2 in venous blood?
PO2 = 40 mmHg
PCO2 = 45 mmHg
(This only shows what’s dissolved in solution)
Hemoglobin and PO2
Watch lecture at 36 min
How would adding hemoglobin to plasma affect PO2?
It would decrease it (hb would take up oxygen, so there would be less in the plasma)
Oxygen and CO22 diffusion
Watch lecture at 46.5 mins
Respiratory quotient (respiratory exchange ratio)
- A reflection of cellular respiration in the body (how even the exchange of oxygen and CO2 is in the body)
Other than exercise, what affects your respiratory exchange ratio?
What molecule you happen to be metabolizing at the cellular level
What would the respiratory exchange ratio be if the only thing we metabolized was sugar?
1
RER for metabolizing fat and why
0.7
You have to give more oxygen to a fat molecule to get CO2 out (with a sugar molecule, you give 6 oxygen molecules, you get 6 CO2 out)
What does a mismatch in RER mean?
- Volume of air inspired is greater than expired
- We bring more O2 in than CO2 out
What is the equation for respiratory exchange ratio?
VCO2/VO2
Graph of %length of capillary vs. pulmonary capillary PO2
Partial pressure of oxygen if capillary (adjacent to alveolus) is 1mm long
- The PO2 going in is 40 mmHg and 100 mmHg as it comes out
- At 1/3 of the way through the capillary, there is already 100% equilibration (with alveolus)
- The reason for the extra length is that when you need to oxygenate more blood per minute, the velocity of blood flowing through your lungs increases and the amount of time that the blood spends in the 1mm long capillary decreases, but you’d still be able to fully saturate it
How would the time to saturate the capillary with oxygen change during exercise?
Watch lecture at 1 hour
How does the extra length of the capillary help you if you have a diseased lung?
- If you have a disease that limits diffusion, having extra length in the capillary might help you
- But eventually, if there’s a real problem with diffusion, you might not be fully saturating the blood (?)
CO2 partial pressure vs capillary length
Watch lecture at 1:01 hours
Diagram showing structure of alveoli with normal lung vs. different diseases
How does pulmonary edema affect exchange of gases in alveoli?
- There is an increased diffusion distance, so there is low PO2 in the blood (lower than PO2 in alveoli)
- This indicates that diffusion is not effective
How does emphysema affect exchange of gases in alveoli?
- Diffusion is limited by decreased surface area of alveoli (smaller alveoli collapse)
- Breathing difficulties
- PO2 in the alveolus can be normal or low, depending on how severe the breathing problem is
- If the PO2 in the alveolus is low, then the diffusion gradient pushing oxygen into the blood is lower (along with problems in diffusion)
- PO2 in the blood will always be low
Symptoms of emphysema
- Difficulty exhaling air (↑airway small airway resistance due to loss of elasticity in lungs; loss of elastic fibers which hold small airways open)
- Low arterial PO2 (↓VE; ↓lung surface area)
What is the compensation for ↑airway resistance for people with emphysema?
- Breath at high lung volumes (more stretch on remaining elastic fibers to hold small airways open)
- Breath against pursed lips (introduce resistance outside the lungs to back up air pressure throughout the lumen of small airways thereby keeping them open)
Does emphysema make inhaling or exhaling more difficult and why?
- It’s particularly difficult to exhale
- The elastic fibers that help keep airways open are broken down, so the small airways have a higher tendency to collapse
- This causes an increase in airway resistance because they’re not being held open by the elastic fibers
Alveolar gas exchange equation for CO2
