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Questions and Answers
If a gas is diffusion-limited, what determines the rate of diffusion across the alveolar-capillary unit?
If a gas is diffusion-limited, what determines the rate of diffusion across the alveolar-capillary unit?
Which type of gas transfer is limited by the flow rate of blood through the pulmonary capillary?
Which type of gas transfer is limited by the flow rate of blood through the pulmonary capillary?
What is the primary factor that limits the amount of gas transferred in diffusion-limited transfer?
What is the primary factor that limits the amount of gas transferred in diffusion-limited transfer?
Which component plays a key role in determining if gas transfer is perfusion-limited or diffusion-limited?
Which component plays a key role in determining if gas transfer is perfusion-limited or diffusion-limited?
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What happens to the rate of diffusion when comparing two gases with different molecular weights, according to Graham's law?
What happens to the rate of diffusion when comparing two gases with different molecular weights, according to Graham's law?
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Why should O2 diffuse faster than CO2 based on molecular weight alone?
Why should O2 diffuse faster than CO2 based on molecular weight alone?
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Which gas has a higher solubility coefficient compared to O2?
Which gas has a higher solubility coefficient compared to O2?
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How does stretched alveoli at high lung volumes affect membrane thickness?
How does stretched alveoli at high lung volumes affect membrane thickness?
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What is the main factor that determines oxygen diffusion under normal resting conditions?
What is the main factor that determines oxygen diffusion under normal resting conditions?
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In what condition can oxygen become diffusion-limited?
In what condition can oxygen become diffusion-limited?
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Which of the following is a factor that limits oxygen diffusion?
Which of the following is a factor that limits oxygen diffusion?
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What is one of the pathologies that can lead to an increased thickness of the alveolar-capillary membrane?
What is one of the pathologies that can lead to an increased thickness of the alveolar-capillary membrane?
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Why do conditions of respiratory membrane impairment reflect as hypoxia instead of hypercapnia?
Why do conditions of respiratory membrane impairment reflect as hypoxia instead of hypercapnia?
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What is the main reason there is normally no diffusion limitation for the exchange of CO2?
What is the main reason there is normally no diffusion limitation for the exchange of CO2?
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What is the composition of arterial blood in terms of partial pressures with hyperventilation?
What is the composition of arterial blood in terms of partial pressures with hyperventilation?
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What is the main cause of hyperventilation?
What is the main cause of hyperventilation?
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What effect does hypocapnia have on the respiratory system?
What effect does hypocapnia have on the respiratory system?
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In hyperventilation, what happens to the resting potential of muscle cells?
In hyperventilation, what happens to the resting potential of muscle cells?
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What is the effect of hypoventilation on arterial blood partial pressures?
What is the effect of hypoventilation on arterial blood partial pressures?
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What physiological response is triggered by hypoxia due to hypoventilation?
What physiological response is triggered by hypoxia due to hypoventilation?
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What is the main process involved in the movement of gases through the conducting airways?
What is the main process involved in the movement of gases through the conducting airways?
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How does oxygen primarily move through the respiratory airways?
How does oxygen primarily move through the respiratory airways?
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According to Henry’s Law, what happens to the solubility of a gas in a liquid as its partial pressure increases?
According to Henry’s Law, what happens to the solubility of a gas in a liquid as its partial pressure increases?
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What is the major consideration regarding the diffusion of O2 and CO2 in the lungs?
What is the major consideration regarding the diffusion of O2 and CO2 in the lungs?
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What does Fick’s Law of Diffusion describe?
What does Fick’s Law of Diffusion describe?
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How does gas movement occur in the conducting airways?
How does gas movement occur in the conducting airways?
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What is the impact of lower temperature on gas solubility according to Henry's Law?
What is the impact of lower temperature on gas solubility according to Henry's Law?
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What is the main process involved in oxygen transport from RBCs to tissues?
What is the main process involved in oxygen transport from RBCs to tissues?
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What effect does hyperventilation have on the composition of arterial blood?
What effect does hyperventilation have on the composition of arterial blood?
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Which condition is likely to cause respiratory alkalosis?
Which condition is likely to cause respiratory alkalosis?
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What physiological effect does hypocapnia have on the respiratory system?
What physiological effect does hypocapnia have on the respiratory system?
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What is the primary cause of hyperventilation?
What is the primary cause of hyperventilation?
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What impact does hypoventilation have on PaO2?
What impact does hypoventilation have on PaO2?
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Which condition results in respiratory acidosis?
Which condition results in respiratory acidosis?
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What effect does hypopolarization have on muscles?
What effect does hypopolarization have on muscles?
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Restrictive diseases result in difficulty expiring.
Restrictive diseases result in difficulty expiring.
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Maximum voluntary ventilation (MVV) primarily provides information about lung capacities.
Maximum voluntary ventilation (MVV) primarily provides information about lung capacities.
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FRC primarily changes due to alterations in TLC.
FRC primarily changes due to alterations in TLC.
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Asthma is characterized by low FEV1/FVC ratio.
Asthma is characterized by low FEV1/FVC ratio.
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FEV1/FVC > normal in obstructive diseases.
FEV1/FVC > normal in obstructive diseases.
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Study Notes
Respiratory System Overview
- The respiratory system combines three main processes to provide oxygen to cells: respiration, circulation, and metabolism.
Gas Movement
- Gas movement occurs through two mechanisms: bulk flow and diffusion.
- Bulk flow:
- Gas movement through the conducting airways results from differences in total pressure.
- External convection (mass movement or convection) and internal convection also occur.
- Diffusion:
- Gas movement in the respiratory airways occurs according to their own partial pressures.
- Oxygen must dissolve in and diffuse through the alveolar-capillary barrier.
Henry's Law
- States that at a constant temperature, the amount of gas that dissolves in a solution is directly proportional to the partial pressure of that gas over the solution.
- Factors affecting solubility: temperature (lower temperature = increased solubility, higher temperature = decreased solubility) and solubility coefficient (O2 = 0.003 mL/dL/mmHg, CO2 = 0.06 mL/dL/mmHg).
Dissolved Oxygen
- Only the part of the gas that is dissolved contributes to the partial pressure of oxygen in blood.
- Gases diffuse according to their individual partial pressure gradients.
Fick's Law of Diffusion
- Describes the rate of diffusion of a gas through a tissue sheet.
- The rate of diffusion of a gas is directly proportional to:
- The surface area available for diffusion (increased surface area increases the rate of diffusion)
- The diffusion coefficient (solubility and molecular weight of the gas)
- The partial pressure difference driving diffusion (higher gradient = faster rate of diffusion)
- Inversely proportional to the thickness of the membrane (increased thickness decreases the rate of diffusion)
Limitations of Gas Transfer
- Important partial pressures of a gas when determining the rate of diffusion include: alveolar, mixed venous blood, and pulmonary capillary blood.
- Perfusion-limited transfer equilibrates, while diffusion-limited transfer does not.
Oxygen and CO2 Transfer
- Oxygen is normally a perfusion-limited gas, while CO2 is more soluble and does not have difficulty with diffusion.
- Factors that limit O2 diffusion: loss of surface area, reduced alveolar partial pressure, decreased time available for exchange, and increased thickness of the alveolar-capillary membrane.
Diffusing Capacity or Transfer Factor
- Measures the lungs' ability to exchange gas.
- The diffusing capacity of the lung is determined by both the diffusing capacity of the membrane and reaction with hemoglobin.
Oxygen Consumption
- At rest, humans consume about 250 mL O2/minute.
- Oxygen consumption is limited by maximal cardiac output, mitochondrial density, and respiratory limitations.
Altered Rates of Ventilation
- Hyperventilation: composition of alveolar air approaches that of tracheal or ambient air, resulting in increased PO2 and decreased PCO2 (hypocapnia).
- Hypoventilation: composition of arterial blood partial pressures change, resulting in decreased PO2 and increased PCO2 (hypercapnia).### Respiratory System Overview
- The respiratory system combines three main processes to provide oxygen to cells: respiration, circulation, and metabolism
- Respiration involves gas movement through bulk flow and diffusion
- Circulation involves the transport of oxygen and carbon dioxide through the bloodstream
- Metabolism involves the diffusion of oxygen from peripheral capillaries to mitochondria
Gas Movement
- Gas movement occurs through bulk flow and diffusion
- Bulk flow occurs due to differences in total pressure, resulting in the movement of gases together along the total pressure gradient
- Diffusion occurs due to differences in partial pressures of individual gases, with each gas moving according to its own partial pressure gradient
Henry's Law
- States that the amount of gas that dissolves in a solution is directly proportional to the partial pressure of that gas over the solution
- The higher the partial pressure of the gas, the more it will dissolve in the liquid
- Temperature affects solubility, with lower temperatures increasing solubility and higher temperatures decreasing solubility
- Each gas has its own solubility coefficient, with oxygen being less soluble in plasma than carbon dioxide
Oxygen Dissolution and Transport
- Only dissolved oxygen contributes to the partial pressure of oxygen in blood
- Oxygen diffuses from the alveoli into the bloodstream, where it binds to hemoglobin
- Oxygen is transported from the lungs to the tissues through the bloodstream
- At the tissues, oxygen diffuses from the capillaries into the mitochondria
Fick's Law of Diffusion
- Describes the rate of diffusion of a gas through a tissue sheet
- The rate of diffusion is directly proportional to the partial pressure gradient of the gas
- The rate of diffusion is also affected by the surface area and thickness of the tissue sheet
Limitations of Gas Transfer
- The rate of gas transfer across the alveolar-capillary unit is limited by the rate of pulmonary blood flow
- The amount of gas transferred across the alveolar-capillary unit is also limited by the diffusing capacity of the lung
- The diffusing capacity of the lung is determined by the ability of the gas to diffuse through the respiratory membrane and react with hemoglobin
Diffusing Capacity or Transfer Factor
- Measures the lung's ability to exchange gas
- Is determined by the diffusing capacity of the membrane and the reaction with hemoglobin
- Is affected by factors such as edema, pneumonia, and exercise
Oxygen Consumption
- At rest, humans consume about 250 ml O2/minute
- Oxygen consumption can increase 10-20 times during exercise
- Cardiac output and ventilation increase during exercise to meet the increased oxygen demand
- Oxygen consumption is limited by the maximal cardiac output, mitochondrial density, and respiratory limitations
Altered Rates of Ventilation
- Hyperventilation occurs when the rate of ventilation is increased, resulting in a decrease in PCO2 and an increase in PO2
- Hypoventilation occurs when the rate of ventilation is decreased, resulting in an increase in PCO2 and a decrease in PO2
- Both hyperventilation and hypoventilation can have significant effects on the body's pH and electrolyte balance
Pulmonary Function Tests
- Measure static lung volumes, dynamic lung volumes, and diffusing capacity
- Used to diagnose and evaluate the severity of pulmonary disorders
- Can be used to predict postoperative pulmonary complications
- Interpretation involves comparing recorded values to predicted values, with a value of +20% of predicted considered normal
Interpreting Pulmonary Function Tests
- Evaluate lung volumes and spirometry to determine whether the disorder is obstructive or restrictive
- Review lung volumes, such as FRC, TLC, and RV, to determine if hyperinflation or restriction is present
- Look at FEV1/FVC ratio and FEF25-75% to determine if obstruction is present
- Use the results to diagnose and evaluate the severity of pulmonary disorders
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