Questions and Answers
What is the difference between dead space and shunt?
The imbalance of ventilation-perfusion impairs overall gas exchange.
True
What is the primary function of the lungs?
Gas exchange
What are the potential causes of hypoxemia?
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What determines alveolar PO2 (PAO2)?
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Impaired pulmonary gas exchange causes __________ in tissue PCO2.
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What are the normal PO2 and PCO2 in the air?
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Hypoxemia is characterized by an abnormally low PO2 in arterial blood.
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Hypoventilation causes which of the following?
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What is V/Q mismatch?
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Normal V/Q ratio is __________.
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What causes an increase in V/Q?
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What are symptoms of V/Q mismatch?
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How is V/Q mismatch measured?
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Study Notes
Dead Space vs Shunt
- Dead space: area where ventilation occurs without perfusion.
- Shunt: area where perfusion occurs without ventilation.
Ventilation-Perfusion Imbalance
- Imbalance impairs overall gas exchange, leading to hypoxemia.
Primary Lung Function
- Lungs primarily facilitate gas exchange, particularly oxygen and carbon dioxide.
Causes of Hypoxemia
- Factors include hypoventilation, diffusion limitation, shunt, and V/Q mismatch.
V/Q Mismatch
- Most common cause of hypoxemia in patients with respiratory disease.
Alveolar PO2 Determinants
- Alveolar PO2 (PAO2) is determined by oxygen removal by blood and replenishment by ventilation.
Tissue PCO2 Increase
- Impaired pulmonary gas exchange results in an increase in tissue PCO2.
Atmospheric PO2 and PCO2
- Normal atmospheric PO2: 150 mmHg; PCO2: 0 mmHg.
PO2 Distribution
- Different organs receive varying amounts of PO2.
PO2 Gradient
- PO2 decreases from the atmosphere to mitochondria as gas is utilized.
Hypoxemia Levels
- Normal: 80-100 mmHg
- Mild: 60-79 mmHg
- Moderate: 40-59 mmHg
- Severe: less than 40 mmHg
Hypoventilation
- Occurs when ventilation is insufficient to clear CO2, leading to increased arterial PCO2.
- Common in obstructive lung diseases.
Hypoventilation Effects
- Causes an increase in arterial PCO2, decrease in PO2 unless supplemental oxygen is given.
- Hypoxemia can be reversed by administering oxygen.
Diffusion Limitation
- Occurs when gas exchange is hindered due to thickened or damaged alveolar-capillary membranes.
- Classic sign is hypoxemia during exercise, but not at rest.
Shunt Effects
- Blood enters the arterial system without going through ventilated lung areas, contributing to hypoxemia.
- Does not increase arterial PCO2 due to chemoreceptor responses.
Summary on Shunt
- Hypoxemia does not improve with 100% oxygen due to bypassed alveoli not being exposed to higher oxygen levels.
V/Q Mismatch Consequences
- Causes hypoxemia and hypercapnia (CO2 retention).
V/Q Inequality in Patients
- Patients with V/Q inequality, such as COPD, can have normal PCO2 due to compensatory increased ventilatory drive.
V/Q Definition
- V/Q indicates how well alveolar ventilation compares to pulmonary capillary perfusion.
Normal V/Q Ratio
- Normal V/Q ratio is 0.8, indicating optimal gas exchange with matched ventilation and perfusion.
Shunt Characteristics
- V/Q equals 0: no ventilation, but perfusion occurs. Results in decreased O2 and increased CO2.
Dead Space Characteristics
- V/Q is greater than 1: ventilation occurs without perfusion. Results in increased O2 and decreased CO2.
Factors Affecting V/Q
- Ventilation and perfusion vary throughout the lungs due to gravity and other factors. Higher V/Q at the lung apex, lower at the base.
Importance of V/Q
- V/Q is critical for determining gas exchange efficacy in lung units. Mismatches reduce overall gas exchange efficiency.
Diseases Decreasing V/Q
- Conditions causing decreased V/Q include chronic bronchitis, asthma, pulmonary embolism, and pneumonia.
Diseases Increasing V/Q
- Conditions resulting in increased V/Q include emphysema and pulmonary hypertension.
Summary of V/Q Mismatch
- Responds to 100% O2, with increased A-a gradient; causes include COPD, pulmonary fibrosis, and pneumonia.
Hypoxemia and A-a Difference
- Hypoventilation: no A-a difference, good O2 response.
- Diffusion limitation: increased A-a, good O2 response.
- Shunt: increased A-a, modest O2 response.
- V/Q inequality: increased A-a, good O2 response.
Symptoms of V/Q Mismatch
- Common symptoms include fatigue, headache, dizziness, shortness of breath (SOB), rapid breathing, confusion, and cyanosis.
Measuring V/Q Mismatch
- V/Q scans assess ventilation and perfusion in the lungs using x-ray technology to identify mismatches.
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Description
This flashcard quiz focuses on the ventilation-perfusion relationships from Chapter 5 of Respiratory Physiology. It covers key concepts like dead space, shunt, gas exchange, and the causes of hypoxemia. Test your understanding of these critical topics in respiratory function.
