Exam 3: 27 Mar Gas Exchange and Transport Mechanisms in the Body Flashcards
What is the significance of hemoglobin saturation in blood?
Indicates the amount of oxygen carried by hemoglobin.
How is carbon dioxide (CO2) primarily transported in the blood?
In three forms: dissolved CO2, carbamino compounds, and bicarbonate.
What is the Haldane effect?
Deoxyhemoglobin has a greater capacity for CO2 transport.
What is the normal CO2 content in arterial blood?
About 48 mls of CO2 per deciliter of blood.
What is the normal CO2 content in venous blood?
About 52.5 mls of CO2 per deciliter of blood.
What is the impact of CO2 on blood pH?
CO2 liberation causes a drop in pH due to proton release.
What is the V/Q ratio?
The ventilation-perfusion ratio, normal values around 0.8.
Fill in the blank: Surfactant helps prevent alveolar _______.
collapse.
What is the primary form of CO2 in blood?
Bicarbonate (HCO3-), about 90% in venous circulation.
True or False: CO2 is less soluble in water than oxygen.
False.
What is the typical PCO2 in arterial blood?
About 40 mmHg.
What does a right shift in the oxygen dissociation curve indicate?
Decreased affinity of hemoglobin for oxygen.
What does a left shift in the oxygen dissociation curve indicate?
Increased affinity of hemoglobin for oxygen.
What is the formula for calculating the partial pressure of a gas?
Partial Pressure = Concentration × Gas Constant.
Fill in the blank: The primary buffer for protons in blood is _______.
Hemoglobin.
What is the role of the chloride-bicarbonate exchanger?
Facilitates the exchange of bicarbonate out of red blood cells.
What does the term ‘physiologic dead space’ include?
Anatomical dead space and alveolar dead space.
What is the impact of anesthesia on the V/Q ratio?
Can lead to abnormal ventilation or perfusion matching.
What is the significance of Laplace’s law in relation to alveoli?
Predicts air moves from smaller to larger alveoli, but surfactant prevents collapse.
What happens to CO2 in the lungs?
It is unloaded into the alveoli due to a concentration gradient.
Fill in the blank: The mixed expired PCO2 is approximately ______ mmHg.
120.
What is the purpose of calculating mixed expired gases (MEG)?
To estimate alveolar dead space and gas exchange efficiency.
True or False: CO2 is less soluble than oxygen in water.
False.
What factors affect gas diffusion?
Thickness of barrier, surface area, pressure difference.
What is the estimated mixed expired PO2?
Approximately 27 mmHg.
What does the dotted line in the graph represent?
About 70% hemoglobin saturation
What is the Haldane effect?
The phenomenon where deoxygenated blood has more capacity to transport CO2
What is the approximate CO2 content in blood when using the corrected CO2 dissociation curve?
About 52.5 mL CO2 per deciliter of blood
What is the role of carbonic anhydrase in red blood cells?
It speeds up the reaction of CO2 combining with water to form carbonic acid
What happens to bicarbonate in red blood cells as CO2 is loaded?
Bicarbonate leaves the red blood cell via a chloride-bicarbonate exchanger
What is the primary buffer for protons in red blood cells?
Hemoglobin
True or False: Oxyhemoglobin has a high affinity for protons.
False
What happens to hemoglobin’s affinity for oxygen when CO2 levels increase?
Affinity decreases, promoting oxygen unloading
Fill in the blank: The typical time for gas exchange to occur in pulmonary capillaries is _______.
0.25 seconds
What is the PO2 of blood entering pulmonary capillaries?
Approximately 40 mmHg
How long does blood typically remain in pulmonary capillaries at rest?
About 0.75 seconds
What effect does increased cardiac output have on the time blood spends in pulmonary capillaries?
It may decrease the time to about 0.25 seconds
What happens to nitrous oxide during gas exchange?
It equilibrates quickly due to its low solubility in blood
Why is carbon monoxide used in pulmonary function tests?
It mirrors the diffusion characteristics of oxygen
What happens to bicarbonate and protons during CO2 unloading in the lungs?
Bicarbonate enters red blood cells while protons are released
What is the primary reason for the fast onset and offset of nitrous oxide?
Its low solubility in blood
How does the solubility of nitrous oxide compare to oxygen?
Nitrous oxide is less soluble than oxygen
What is the relationship between the diffusion of carbon monoxide and oxygen?
They have similar diffusion characteristics
What is the effect of protons on hemoglobin’s affinity for oxygen?
Increased protons decrease hemoglobin’s affinity for oxygen
True or False: Deoxyhemoglobin has a higher affinity for oxygen compared to oxyhemoglobin.
False
What is the primary source of CO2 in the peripheral tissues?
Metabolism as a byproduct
What is the primary use of carbon monoxide in diagnostic tests?
To assess the diffusion capabilities of the lungs
Carbon monoxide is used because its absorption rate can indicate how well gases diffuse in the lungs.
What indicates a problem with gas diffusion when using carbon monoxide as a diagnostic gas?
Slow absorption of carbon monoxide
If carbon monoxide is absorbed slowly, it suggests issues with gas diffusion across the alveoli.
What is the expected carbon monoxide level in a healthy person’s blood sample?
0% carbon monoxide
Healthy individuals should not have significant levels of carbon monoxide unless exposed to specific environments.
During extreme exercise, how long does blood spend in the pulmonary capillaries?
About a quarter of a second
This brief duration is sufficient for oxygen uptake under high demand.
How long does blood typically spend in the pulmonary capillaries under normal conditions?
About three quarters of a second
This duration allows for adequate gas exchange even if diffusion capacity is slightly impaired.
What happens to diffusing capacity if it is one quarter of normal?
It takes three quarters of a second for O2 levels to equilibrate
This indicates compromised diffusion, often due to conditions like pneumonia.
What characterizes a diffusion-limited gas exchange?
No equilibration between pulmonary capillary blood and alveolar air
This indicates that the rate of diffusion is insufficient for gas exchange.
What is the definition of perfusion-limited gas exchange?
Gas exchange depends on blood flow through the lungs
Oxygen absorption is limited by the amount of blood moving through the pulmonary capillaries.
What is the relationship between diffusion capacity and the thickness of the barrier for gas exchange?
Thicker barriers decrease the speed of gas exchange
Increased thickness requires gases to travel further, slowing diffusion.
How does surface area affect gas diffusion in the lungs?
Greater surface area increases gas diffusion
Healthy lungs have a large surface area, facilitating efficient gas exchange.
What is the impact of pressure difference on gas diffusion rates?
Greater pressure difference increases diffusion rate
A larger gradient drives gases from areas of higher pressure to lower pressure.
What does the term ‘diffusivity’ refer to in gas exchange?
It combines gas solubility and molecular weight
Diffusivity affects how quickly a gas can move across a barrier.
How much more soluble is CO2 compared to O2?
24 times more soluble
This solubility plays a significant role in gas exchange efficiency.
What is the normal V/Q ratio in a healthy individual?
Approximately 0.8 to 0.85
This ratio reflects the balance between ventilation and perfusion in the lungs.
What happens to the V/Q ratio if ventilation decreases?
The V/Q ratio decreases
A smaller numerator leads to a lower overall fraction.
What occurs to the V/Q ratio when perfusion is absent?
The V/Q ratio increases
Dividing by a smaller number results in a higher fraction.
What is the limit of the V/Q ratio?
Infinity
This occurs if ventilation is present without any perfusion.
What happens to the v Q Ratio when divided by a smaller number?
The v Q Ratio is going to be higher than normal.
What is the absolute limit of the v Q Ratio?
The limit is infinity.
What occurs when attempting to divide by zero?
It results in a calculator error.
What is a shunt in terms of blood flow?
Blood flow through a non-ventilated alveolus.
What is the extreme case of the v Q Ratio during no blood flow but ventilation?
The v Q Ratio can be as high as infinity.
What is alveolar dead space?
A condition with lots of ventilation but less blood flow.
What is expected from blood leaving an area with more ventilation than perfusion?
Higher oxygen and lower CO2.
What is expected from blood leaving an area with more perfusion than ventilation?
Lower oxygen than average.
How does the v Q Ratio differ between the top and bottom of the lungs?
The base has higher blood flow and ventilation than the top.
What is the typical PO2 at the base of the lung?
About 90 mmHg.
What is the typical PCO2 at the apex of the lung?
Around 30 mmHg.
What is the average PCO2 of expired breath?
About 40 mmHg.
What is the expected PO2 in normal alveolar ventilation?
Around 100 mmHg.
The base of the lung is generally under-ventilated or over-ventilated?
Under-ventilated.
The top of the lung is generally under-ventilated or over-ventilated?
Over-ventilated.
What effect does aging have on v Q matching?
B Q matching typically gets worse with age.
What happens to lung conditions during anesthesia without positive pressure?
Areas of the lungs can collapse (atelectasis).
What is the effect of applying PEEP during anesthesia?
It helps prevent atelectasis.
What is the significance of the curves in the graphs of ventilation and blood flow?
They show the matching of ventilation and perfusion.
What occurs to v Q Ratio when a patient is anesthetized?
The v Q Ratio can become poorly matched.
What is the relationship between ventilation and perfusion at the base of the lung?
More blood flow than ventilation.
What is the relationship between ventilation and perfusion at the apex of the lung?
More ventilation than blood flow.
Fill in the blank: The v Q Ratio at the base of the lung is typically _____ than average.
lower
Fill in the blank: The v Q Ratio at the apex of the lung is typically _____ than average.
higher
What is the key characteristic of Miller’s anesthesia?
It induces effects almost instantaneously.
This refers to the rapid onset of anesthesia as discussed in the context.
What happens to air pressure in smaller and larger connected alveoli according to Laplace’s law?
Air moves from smaller spheres to larger spheres due to pressure differences.
Laplace’s law predicts that the pressure in smaller alveoli is higher than in larger ones.
What is the formula relating pressure in a sphere to surface tension and radius?
Pressure = Surface tension / Radius.
This formula indicates that smaller radii lead to higher pressures.
What role does surfactant play in alveoli?
Surfactant reduces surface tension, helping to distribute air more evenly.
Surfactant prevents uneven ventilation among alveoli.
What is anatomical dead space and its average volume in a healthy adult?
Anatomical dead space is about 150 cc.
This is a constant volume in most healthy individuals.
What is the primary cause of alveolar dead space in patients?
Alveolar dead space develops due to impaired gas exchange, often from anesthesia or lung disease.
Positive pressure ventilation can hinder blood flow through capillaries.
What is mixed expired gas and what does it consist of?
Mixed expired gas is a combination of alveolar air and dead space air.
It includes air that has undergone gas exchange and air that has not.
How does the presence of dead space affect the composition of mixed expired gases?
It lowers the expected PCO2 in mixed expired gases.
More dead space means less CO2 is being exchanged.
What happens to the effectiveness of surfactant in collapsed alveoli over time?
Surfactant concentration decreases as alveoli collapse, leading to uneven ventilation.
Macrophages can degrade surfactant in collapsed regions.
What is the relationship between the P O2 of mixed expired gas and its components?
It is between the P O2 of dead space air and alveolar air, closer to the latter.
This reflects the greater volume of alveolar air in the mixture.
What is the expected PCO2 in dead space air?
The PCO2 in dead space air is zero.
This is because no CO2 is exchanged in the anatomical dead space.
What is the anatomical dead space volume estimation formula based on ideal body weight?
Anatomical dead space = 1 mL per pound of ideal body weight.
For example, a 150-pound person would have 150 cc of anatomical dead space.
What happens to the partial pressure of nitrogen in mixed expired gas?
It remains similar to the nitrogen pressure that went into the lungs.
Nitrogen is generally inert and doesn’t change significantly during gas exchange.
What is the impact of surfactant deficiency on lung function?
It leads to uneven distribution of fresh air and impaired gas exchange.
Every lung problem studied has shown a surfactant deficiency.
Fill in the blank: Surfactant helps correct or prevent _______ predictions from occurring.
Laplace’s.
Surfactant counteracts the uneven ventilation predicted by Laplace’s law.
True or False: The PCO2 of mixed expired gas is always higher than that of dead space air.
True.
Alveolar air contributes to the PCO2 in mixed expired gas.
What is the alveolar PCO2 value?
40
What should the PCO2 in dead space be?
0
What is the formula for the partial pressure of a gas?
Partial pressure = concentration × total pressure
At sea level, what is the total pressure used to calculate CO2 concentration?
760 mmHg
What is the concentration of CO2 in alveolar air?
5.3%
How do you calculate the amount of CO2 in alveolar air?
Concentration × Volume
What is the volume of alveolar air used in the calculation?
350 cc
What is the amount of CO2 in alveolar air?
18.42 mL
What is the total volume when combining dead space air and alveolar air?
500 cc
What is the new concentration of CO2 in the mixed sample?
3.7%
How is the PCO2 of the mixed sample calculated?
Concentration × Total pressure
What is the calculated PCO2 value of the mixed sample?
28 mmHg
True or False: The dead space air composition is similar to the alveolar air composition.
False
What should you do to calculate the mixed expired PCO2?
Divide the total CO2 by the total size of the sample and multiply by total pressure
What would be an expected mixed expired PO2 value?
120 mmHg
Fill in the blank: The concentration formula is useful for determining _______.
volume
What can you figure out using the concentration of a substance?
Partial pressure or volume of gas
