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Questions and Answers
How does an increased ventilation-perfusion ratio affect alveolar and capillary gas pressures?
How does an increased ventilation-perfusion ratio affect alveolar and capillary gas pressures?
- Increases alveolar oxygen pressure while decreasing alveolar carbon dioxide pressure; effect on capillary pressures is variable. (correct)
- Increases both alveolar and capillary oxygen pressures while decreasing carbon dioxide pressures.
- Decreases both alveolar and capillary oxygen pressures while increasing carbon dioxide pressures.
- Decreases alveolar oxygen pressure while increasing alveolar carbon dioxide pressure; effect on capillary pressures is minimal.
What is the approximate normal overall ventilation-perfusion ratio (V/Q) in a healthy lung?
What is the approximate normal overall ventilation-perfusion ratio (V/Q) in a healthy lung?
- 0.8 (correct)
- 2.0
- 0.5
- 1.2
In an upright lung, how does the ventilation-perfusion ratio change from the apex to the base?
In an upright lung, how does the ventilation-perfusion ratio change from the apex to the base?
- It decreases from apex to base. (correct)
- It remains constant throughout the lung.
- It increases from apex to base.
- It fluctuates randomly without a specific pattern.
What primarily determines the partial pressure of oxygen (PAO2) in the alveoli?
What primarily determines the partial pressure of oxygen (PAO2) in the alveoli?
Which of the following conditions would most likely lead to a decreased ventilation-perfusion ratio in a lung region?
Which of the following conditions would most likely lead to a decreased ventilation-perfusion ratio in a lung region?
How is the respiratory quotient (RQ) defined?
How is the respiratory quotient (RQ) defined?
In which scenario would the respiratory exchange ratio (RR) be most likely equal to the respiratory quotient (RQ)?
In which scenario would the respiratory exchange ratio (RR) be most likely equal to the respiratory quotient (RQ)?
What is the primary factor that causes blood flow to be greater in the lower regions of the lung compared to the upper regions in an upright person?
What is the primary factor that causes blood flow to be greater in the lower regions of the lung compared to the upper regions in an upright person?
A patient has a respiratory rate of 15 breaths/min and a tidal volume of 400 mL. What is the patient's minute ventilation?
A patient has a respiratory rate of 15 breaths/min and a tidal volume of 400 mL. What is the patient's minute ventilation?
How does a pulmonary embolism typically affect the ventilation-perfusion ratio in the affected area of the lung?
How does a pulmonary embolism typically affect the ventilation-perfusion ratio in the affected area of the lung?
Which of the following scenarios would result in a V/Q ratio approaching infinity?
Which of the following scenarios would result in a V/Q ratio approaching infinity?
A construction worker is impaled by a steel rod and loses a significant amount of blood. How does this affect the alveolar ventilation?
A construction worker is impaled by a steel rod and loses a significant amount of blood. How does this affect the alveolar ventilation?
What is the primary effect of an upper airway obstruction, such as a foreign object lodged in the trachea, on the ventilation-perfusion ratio?
What is the primary effect of an upper airway obstruction, such as a foreign object lodged in the trachea, on the ventilation-perfusion ratio?
Clinically, approximately how much oxygen is consumed by the cells in the body under normal conditions?
Clinically, approximately how much oxygen is consumed by the cells in the body under normal conditions?
If a patient's respiratory quotient (RQ) is measured to be 0.7, what does this value indicate?
If a patient's respiratory quotient (RQ) is measured to be 0.7, what does this value indicate?
Which respiratory disorder results in destruction of pumonary vessels and decreases cardiac output?
Which respiratory disorder results in destruction of pumonary vessels and decreases cardiac output?
What lung condition decreases the amount of CO$_2$ returning to alveoli??
What lung condition decreases the amount of CO$_2$ returning to alveoli??
What condition is caused by decreased cardiac output?
What condition is caused by decreased cardiac output?
Which of the following diseases causes a restrictive lung disorder?
Which of the following diseases causes a restrictive lung disorder?
Which zone of the lungs does have a decreased ventilation?
Which zone of the lungs does have a decreased ventilation?
Flashcards
Ventilation-Perfusion Ratio
Ventilation-Perfusion Ratio
The ratio of ventilation to perfusion in the lungs. Normal is about 0.8.
V/Q in Upright Lung
V/Q in Upright Lung
In the normal upright lung, the V/Q ratio is higher in the upper regions (apices) due to less blood flow and lower in the lower regions due to increased blood flow.
Increased V/Q Effects
Increased V/Q Effects
An increased V/Q ratio leads to increased PAO2 and decreased PACO2 in the alveoli.
Decreased V/Q Effects
Decreased V/Q Effects
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Respiratory Quotient (RQ
Respiratory Quotient (RQ
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Respiratory Exchange Ratio (RR)
Respiratory Exchange Ratio (RR)
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Disorders Increasing V/Q
Disorders Increasing V/Q
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Other Causes of Increased V/Q
Other Causes of Increased V/Q
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Disorders Decreasing V/Q
Disorders Decreasing V/Q
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Dead Space Unit
Dead Space Unit
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Shunt Unit
Shunt Unit
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Study Notes
- Ventilation-perfusion ratio is a key concept in respiratory physiology
- Ideally, each alveolus in the lungs should receive the same amount of ventilation and pulmonary capillary blood flow
Ventilation-Perfusion Ratio
- Normal alveolar ventilation is approximately 4 L/min
- Normal pulmonary capillary blood flow is approximately 5 L/min
- The average overall ratio of ventilation to blood flow is 4:5, or 0.8
- The ventilation-perfusion ratio is represented as V/Q
Normal VQ Ratio
- Approximately 0.8
VQ Ratio in the Lungs
- Overall, the V/Q ratio is approximately 0.8, but varies markedly throughout the lung
- In a normal individual in an upright position, alveoli in the upper portions of the lungs (apices) receive a moderate amount of ventilation and little blood flow resulting in a higher ratio in the upper lung region, being higher than 0.8
- In the lower regions of the lung, alveolar ventilation is moderately increased and blood flow is greatly increased because blood flow is gravity-dependent
- This results in a lower ratio, being lower than 0.8
- Thus, the ratio progressively decreases from the top to the bottom in an upright lung, with an average ratio of approximately 0.8
How Ventilation-Perfusion Ratio Affects Alveolar Gases
- The V/Q ratio profoundly affects oxygen and carbon dioxide pressures in alveoli (PA02 and PACO2)
- Normal PA02 and PACO2 are approximately 100 and 40 torr, not the case throughout most alveolar units
- PA02 is determined by the balance between the amount of oxygen entering the alveoli and its removal by capillary blood flow
- PACO2 is determined by the balance between the amount of carbon dioxide that diffuses into alveoli from capillary blood and its removal from alveoli by means of ventilation
Increased V/Q Ratio
- Increased Ventilation-Perfusion Ratio caused by an excessive amount of blood loss
- A construction worker who is impaled by a steel rod: the loss of blood makes the alveolar ventilation ineffective
- Even though the PAo2 and the PaO2 increase in response to the increased V/Q ratio, the actual amount of oxygen being transported has decreased because of the decrease in blood flow
Low V/Q Ratio
- Can develop from either a decrease in ventilation or an increase in perfusion
- PAo2 falls and PACO2 rises
- The PAo2 decreases because the oxygen moves out of the alveolus and into the pulmonary blood faster than it is replenished by ventilation
- Decreased Ventilation-Perfusion Ratio caused by an upper Airway Obstruction
- A 4-year-old baby boy came into ER in severe respiratory distress because the boy inhaled and lodged a quarter in his upper airway
- The low rate of the patients and his fatigue of trying to breath caused his V/Q ratio to drop: His PAo2 decreased while his PAco2 increased
Respiratory Quotient (RQ)
- Internal respiration involves gas exchange between the systemic capillaries and the cells
- Clinically, Respiratory Quotient is the ratio between the volume of Oâ‚‚ consumed (VOâ‚‚) and the volume of CO2 produced (VCO2).
- Under normal conditions, about 250 mL of O2 are consumed by the cells to exchange cells, producing 200mL of CO2 and normal RQ is 0.8
Respiratory Exchange Ratio (RR)
- External respiration involves gas exchange between pulmonary capillaries and alveoli
- Respiratory exchange ratio (RR) is the quantity of O2 and CO2 exchanged during a period of one minute
- Normally, RR and RQ are equal
How Respiratory Disorders Affect the V/Q Ratio
- Pulmonary disorders that increase V/Q ratio:
- Pulmonary emboli
- Partial or complete obstruction in the pulmonary artery or some of the arterioles, e.g., atherosclerosis, collagen disease
- Extrinsic pressure on pulmonary vessels, e.g., pneumothorax, hydrothorax, presence of tumor
- Destruction of pulmonary vessels, e.g., emphysema
- Decreased cardiac output
- Pulmonary disorders that decrease V/Q ratio:
- Obstructive lung disorders, e.g., emphysema, bronchitis, asthma
- Restrictive lung disorders, e.g., pneumonia, silicosis, pulmonary fibrosis
- Hypoventilation from any cause
- Alveolar O2 and CO2 pressure changes occur as a result of V/Q ratio changes caused by respiratory disorders
- Shunt unit
- Normal unit
- Dead space unit
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