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Answer the following questions about the ventilation-perfusion (V/Q) ratio.   A patient has pneumonia in the left...

Answer the following questions about the ventilation-perfusion (V/Q) ratio.  

A patient has pneumonia in the left lower lobe of the lung. The pneumonia has caused bronchoconstriction, pulmonary edema, and alveolar collapse (atelectasis) resulting in a significant decrease in ventilation (V). Describe the V-Q alteration, the body’s response to this V-Q mismatch, and the clinical consequences.




A patient has severe chronic obstructive pulmonary disease which results in a lung-wide decrease in alveolar ventilation. Describe the V-Q alteration, the body’s response to this V-Q mismatch, and the clinical consequences.





A patient has a blood clot in the lungs (pulmonary embolus) resulting in decreased alveolar perfusion (Q). Describe the V-Q alteration, the body’s response to this V-Q mismatch, and the clinical consequences.

Solutions

Expert Solution

Case I :

V-Q alteration : In this case as ventilation decrease, V/Q ratio or ventilation/perfusion ratio will also decrease. That means there is a misbalance between entering oxygen in to the alveoli and removing CO2 from the alveoli. As a result the alveolar levels of oxygen become decrease and the CO2 become increase. That means decreased ventilation (without a compensatory change in perfusion) does not meet our metabolic need for oxygen (the oxygen consumption) in the body.

Body’s rponse : Hyperventilation or over breathing occurs when the rate and quantity of alveolar ventilation of carbon dioxide exceeds the body's production of carbon dioxide. Hyperventilation causes alakalosis, which causes a feedback response of decreased ventilation (to increase carbon dioxide). In this way body meet it’s original CO2 level by removing excess CO2 by breathing.

Clinical consequences : Coughing that may produce mucus, fever, sweating, and chills, shortness of breath, chest pain.

Case II:

V-Q alteration : In this case as ventilation decrease, V/Q ratio or ventilation/perfusion ratio will also decrease. That means there is a misbalance between entering oxygen in to the alveoli and removing CO2 from the alveoli. As a result the alveolar levels of oxygen become decrease and the CO2 become increase. That means decreased ventilation (without a compensatory change in perfusion) does not meet our metabolic need for oxygen (the oxygen consumption) in the body.

Body’s rponse : Hyperventilation or over breathing occurs when the rate and quantity of alveolar ventilation of carbon dioxide exceeds the body's production of carbon dioxide. Hyperventilation causes alakalosis, which causes a feedback response of decreased ventilation (to increase carbon dioxide). In this way body meet it’s original CO2 level by removing excess CO2 by breathing.

Clinical consequences : Difficulty breathing, expiratory wheezing, fast breathing, frequent respiratory infections, rapid breathing, shortness of breath, shortness of breath at night, shortness of breath on exercise, shortness of breath on lying down, or wheezing.

Case III :

V-Q alteration : In this case as perfusion decreases, V/Q ratio or ventilation/perfusion ratio will increase. In this case following events will occur:

  • Increase ventilation (bring in more oxygen to the alveoli, blow off more CO2 from the lungs)
  • Decrease the perfusion (so the blood takes away less oxygen, delivers less CO2).
  • This will lead to an increase in the PAO2 (and therefore PaO2)
  • and a decrease in PACO2 and PaCO2

Body’s rponse : Hypoventilation occurs when ventilation is inadequate (hypo meaning "below") to perform needed gas exchange. By definition it causes an increased concentration of carbon dioxide (hypercapnia) and respiratory acidosis. Hypoventilation causes acidosis, which causes a feedback response of increased ventilation (to remove carbon dioxide).

Clinical consequences : Symptoms of a pulmonary embolism depend on the size of the clot and where it lodges in the lung. The most common symptom of a pulmonary embolism is shortness of breath. This may be gradual or sudden.


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