Questions and Answers
What determines gas transfer between different phases?
Why does CO2 equilibrate rapidly across the alveolar-capillary exchange surface?
What happens to the partial pressure of O2 in the pulmonary capillary blood at rest?
What is the consequence of an disrupted alveolar-capillary unit in respiratory disease?
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Why does CO2 diffuse more rapidly than O2 despite its higher molecular weight?
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What is the direction of CO2 movement in the alveolar-capillary exchange surface?
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What is the characteristic of gas transfer in a normal lung?
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What is the relationship between the diffusion rates of O2 and CO2?
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What is the unit of pressure equivalent to 7.5 mmHg?
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What is the rate of transfer of gas through a sheet of tissue dependent on?
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What is the pressure gradient driving diffusion across the alveolar-capillary membrane?
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What does the diffusing capacity of the lungs (DLg) represent?
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What is the formula to calculate oxygen diffusing capacity (DLO2)?
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Why can mean pulmonary capillary PCO be assumed to be zero in the measurement of carbon monoxide diffusing capacity (DLCO)?
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What is the advantage of using carbon monoxide in the measurement of diffusing capacity?
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What is the purpose of including a tracer gas in the breath inhaled by the patient during the measurement of DLCO?
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What is the effect of an acute ascent to altitude on the oxygen capacity of arterial blood?
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What is the effect of a decrease in pH on the oxygen-haemoglobin dissociation curve?
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What is the effect of an increase in 2,3-DPG on the oxygen-haemoglobin dissociation curve?
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What is the effect of anaemia on the oxygen capacity of arterial blood?
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What is the PO2 at the base camp of Mt Aconcagua, given a barometric pressure of 60kPa?
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What is the effect of an increase in temperature on the oxygen-haemoglobin dissociation curve?
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What is the effect of an increase in PCO2 on the oxygen-haemoglobin dissociation curve?
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What is the oxygen saturation level of resting mixed venous blood?
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What is the primary reason for reduced arterial oxygen content in iron deficiency anemia?
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At high altitude, what is the primary reason for improved physical activity after breathing 100% oxygen for short periods?
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What is the approximate fraction of oxygen in dry air at sea level?
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What is the term for the rate at which oxygen diffuses through the alveolar-capillary membrane?
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Why can CO transfer factor be measured but O2 transfer factor cannot?
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What would be the approximate partial pressure of oxygen on a mountain where the barometric pressure is 50.5 kPa (380 mmHg)?
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Which of the following would NOT cause a low CO transfer factor?
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What would be the primary effect of hypoventilation on gas exchange in the lungs?
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What is the effect of polycythaemia on the oxygen reservoir in severe chronic respiratory failure?
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In severe chronic respiratory failure, why is the patient vulnerable to a small further fall in arterial PO2?
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What is the effect of anaemia on average tissue capillary PO2 compared to a person with a normal Hb concentration?
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Why is the fall in PO2 along the tissue capillary less steep in polycythaemia?
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What is the consequence of a small further fall in arterial PO2 in a patient with severe chronic respiratory failure?
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Why is the patient in severe chronic respiratory failure still vulnerable despite having adequate O2 delivery?
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What is the relationship between the average tissue capillary PO2 and the venous PO2 in severe chronic respiratory failure?
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What is the effect of polycythaemia on the PO2 gradient driving diffusion in severe chronic respiratory failure?
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Study Notes
Gas Exchange and Transport
- Diffusion of O2 and CO2 across the alveolar-capillary membrane is driven by partial pressure gradients.
- O2 diffuses from the alveoli into the pulmonary capillaries, while CO2 diffuses from the pulmonary capillaries into the alveoli.
- The rate of diffusion is affected by the partial pressure gradient, solubility coefficient, and molecular weight.
- CO2 has a higher solubility coefficient than O2, making it 23 times more soluble and allowing it to diffuse 20 times faster.
Factors Affecting Diffusion
- Partial pressure gradient: gas moves down its partial pressure gradient from high to low.
- Area and thickness of the alveolar-capillary membrane: increased surface area and decreased thickness facilitate diffusion.
- Solubility coefficient: gases with higher solubility coefficients diffuse faster.
Measurement of Diffusing Capacity
- Oxygen diffusing capacity (DLO2): measures the rate of O2 transfer from the alveoli to the pulmonary capillaries.
- Carbon monoxide diffusing capacity (DLCO): measures the rate of CO transfer from the alveoli to the pulmonary capillaries.
- DLCO is commonly used in clinical investigations to assess lung function.
Oxygen-Haemoglobin Dissociation Curve
- The curve shows the relationship between oxygen saturation and partial pressure.
- Factors affecting the curve include pH, PCO2, temperature, and 2,3-DPG levels.
Acute Ascent to Altitude
- Arterial oxygen content and saturation decrease due to decreased inspired PO2.
- Oxygen capacity of arterial blood is normal, but oxygen-carrying capacity is reduced.
Anaemia
- Oxygen capacity of arterial blood is reduced due to low haemoglobin levels.
- Arterial oxygen content and saturation are reduced due to decreased oxygen-carrying capacity.
Gaseous Diffusion and Transport Quiz
- Questions to consider:
- What factors affect water vapour pressure in the air we breathe?
- How do changes in barometric pressure affect PO2 and fractional concentration of oxygen in dry air?
- What is meant by "transfer factor" of a gas in the lungs?
- Why can CO transfer factor be measured but O2 transfer factor cannot?
- What causes a low CO transfer factor?
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Description
Learn about the diffusion of oxygen and carbon dioxide across the alveolar-capillary membrane, and how the rate of diffusion is affected by various factors. Quiz yourself on the principles of gas exchange and transport!