Exam 4: Respiratory L3 Flashcards
Transfer of gas across the blood gas barrier:
- Occurs via the process of _____
- Transfer of gas follows basic _____
Factors facilitating gas diffusion in the respiratory system:
1.
2.
3
Occurs via diffusion (passive)
Transfer of gas follows basic diffusion laws
Factors facilitating gas diffusion:
- Large Surface Area of Alveoli (70 meters square = 750 square feet)
- Short distance to travel
- Gases with advantageous diffusion properties
Capillary network is also ideal for gas exchange:
Capillary diameter:
RBC diameter:
Erythrocytes:
- Pass through capillaries in _______
- Average transit time is ___
Capillary diameter: less than ten um
RBC diameter: 7 um
RBCS:
Pass through capillaries in single file
Average transit time is roughly a second
Total diffusion capacity for O2:
Combination of __ different diffusion constants:
12 different diffusion constants
Fick’s Law of Diffusion Through Tissues:
(Parameters: Area, thickness, diffusion constant, partial pressure)
The amount of gas transferred is Proportional to what three things?
What is it inversely proportional to?
Diffusion through tissues:
Amount of gas transferred is proportional to Area, Diffusion Constant, and the Partial Pressure
Amount of gas transferred is inversely proportional to thickness
What will happen to diffusion rate considering the following:
Pulmonary Edema
Collapsed Lung
High Altitude
PE: will cause an increase in thickness, and therefore a decrease in diffusion
Collapsed Lung: decrease in area, decrease in diffusion
High Altitude: Decrease in partial pressure, decrease in diffusion
Both CO2 and O2 can rapidly diffuse across the alveolar barrier, but which one is better?
So, CO2 is better, but both will diffuse readily under normal conditions.
Explain Diffusion Limited:
The amount of X carried into circulation is limited by ________.
Driving force will always be _____ than the rate at which molecules can pass through the barrier.
What are the two general examples of why molecules would be diffusion limited?
Draw the graph and figure for diffusion limited
Diffusion Limited:
- The amount of molecule X carried into circulation is limited by the diffusion across the alveolar membrane
Driving force will always be higher than the rate at which molecules can pass through the barrier.
Two main general examples:
- Molecule simply can’t diffuse across the barrier
- Molecule diffuses but then gets immediately converted to something or binds to something else and therefore no longer contributes to partial pressure
Perfusion Limited:
- The amount of molecule X carried into circulation is limited by _____
Diffusion will quickly ______the driving force
The only way to get more molecule X into circulation is to _______.
Draw both figure and the graph
Perfusion Limited:
Amount of molecule X carried into circulation is limited by the rate of perfusion (blood flow through pulmonary capillaries)
Diffusion will quickly decrease the driving force
Only way to get more molecule X into circulation is to increase perfusion
What is the different shape of the graph between Pressure as a function of time between diffusion limited and perfusion limited molecules
Describe the following gases as perfusion limited or diffusion limited:
N2O (nitrous oxide)
CO (carbon monoxide)
O2 and Co2
N2O is perfusion limited (gas transfer is limited by the amount of blood perfusion the alveoli)
CO is DIFFUSION LIMITED (it binds rapidly to Hb and then doesn’t count as partial pressure anymore)
O2 and CO2 both bind to Hb, but with less affinity than CO, they are perfusion limited under normal circumstaces
What happens to oxygen uptake along the pulmonary capillary under the following circumstances:
- Exercise
- Increased thickness of blood-gas barrier (like if you have fibrosis or edema)
- Exercise: increased blood flow, but under normal circumstances you’re still okay because it’s perfusion limited and at 250 milliseconds you still are at PO2 of 100mmHg
- Increased thickness of blood-gas barrier (fibrosis, or edema):
oxygen uptake may become diffusion limited
Oxygen Uptake along the pulmonary capillary at lower alveolar PO2 (like at high altitude)
What does going to higher altitude do to the driving force/pressure gradient?
Severe exercise at high altitude can lead to _________.
Going to higher altitude will decrease the pressure gradient/driving force because you are decreasing the amount of PO2 in the air.
Severe exercise at high altitude can lead to diffusion impairment of oxygen transfer.
What does DL stand for?
How does it get measured in the clinic?
DL is the diffusion capacity of the lung
DL = VCO / PalveolarCO
CO is used because it diffuses rapidly and it is also not normally present in your blood
Single Breath DL of CO
Pt will breathe in CO (and a trace amount of He), hold for ten seconds, breathe out and then their volume of CO they breathe out will be measured. If diffusion of CO decreases, the graph will not be as steep of a drop off.
Gas diffusion follows basic gas laws:
Diffusion is directly proportional to____
Diffusion is indirectly proportional to____
O2 and CO2 are normally ____ limited
Under extremes (high altitude or exercise) or disease, O2 can become _____
What is used to measure the total diffusion capacity of the lung?
Diffusion is directly proportional to: surface area, the pressure gradient, and also the diffusion constant
Diffusion is inversely proportional to thickness
O2 and CO2 are normally perfusion limited
Under extremes, or disease O2 can become diffusion limited
Single breath CO test is used to measure total diffusion capacity of the lung.
What are the only arteries in the body that carry deoxygenated blood?
Pulmonary arteries
Pulmonary arteries:
Total blood volume is like 500 mL
In the alveolar capillary network:
___ mL under resting conditions
___ during exercise
In alveolar capillary network:
70 mL under normal resting conditions
200 mL during exercise
Pulmonary arteries:
- think wall, ____ smooth muscle
- ________ compliant than systemic arteries
- easily distendable
_____ pressure circulation
Driving Pressure: systemic vs pulmonary:
Pulmonary arteries:
- think wall, minimal smooth muscle
- 7x more compliant than systemic arteries
- easily distendable
LOW pressure circulation
Driving Pressure:
Systemic: 87 mmHg
Pulmonary: 6 mmHg
What are the four factors influencing lung perfusion:
1.
2.
3.
4.
Factors Influencing Lung Perfusion:
- Pulmonary Vascular Resistance (PVR)
- Gravity
- Alveolar Pressure
- Arterial venous pressure gradient
Pulmonary Vascular Resistance:
Explain/graph how PVR changes with increasing vascular pressure (in arteries and in veins)
What two mechanisms help with this process?
PVR decreases with increasing vascular pressure
MUCH more of a change in PVR with increasing pressure in the arterial side
Two Mechanisms:
1. Recruitment : opening of closed vessels and conducting in previously non conducting vessels
- Distension: widening of open vessels
For the blood vessels within the respiratory system:
Alveolar vessel : feels pressure from ____
Extra-alveolar vessel: feels pressure from
Alveolar Vessels: subject to pressure from alveoli
Extra-alveolar vessel: subject to pleural pressure
Draw the graph showing how PVR changes with lung volumes for the alveolar and extraalveolar vessels
At which point is PVR the lowest?
PVR is the lowest at FRC (“steady state”)
At low lung volume, extra-alveolar vessels are subject to intrapleural pressure
At high lung volume, vessel stretching crishes alveolar vessels, pulls open extra-alveolar vessels
Explain the affect that gravity has on distribution of pulmonary flow
Just like with ventilation,
most of the blood flow goes to the base instead of the apex.
Blood flow distrubution depends on posture
Difference between apex and base becomes less during exercise