Why does pulmonary oedema give pink frothy sputum?

  1. Hello everyone,

    You usually get pulmonary oedema in conditions such as Left heart failure, where there is increasesd back pressure in pulmonary vasculature, which in turn increase hydrostatic pressure and then fluid in alveoli giving rise to the condition. Now my question is this fluid in alveoli is a transduate it does not contain blood, however the classic symptom of this condition is pink frothy sputum which indicates blood. Why is this the case. Thanks :smile:
     
  2. jcsd
  3. Simon Bridge

    Simon Bridge 15,261
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    The blood, where it appears, comes from associated tissue damage.
    The damage may even be the cause of the condition.
     
  4. Thanks for the reply Simon :smile: But pulmonay oedema is an transduate, capillaries don't get damaged. I don't understand.
     
  5. Simon Bridge

    Simon Bridge 15,261
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    You are thinking about the problem backwards - you deduce from the definition of the condition that there is no damage and therefore blood cannot appear as a symptom accompanying the condition. What you should be thinking is that blood definately does appear in connection with the condition, therefore damage must occur - if not by the condition itself than in relation to the condition. How many different ways can a patient damage their lungs?

    Do you think that the presence of a pulminary oedema somehow protects capillaries from subsequent damage? Say from violent coughing brought on by having fluid in the airways? Could the increased pulmonory BP also rupture capilliaries? What about those cases where physical trauma to the tissue is the cause of the oedema?
     
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