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A pulmonary shunt is a physiological condition which results when the alveoli of the lungs are perfused with blood as normal, but ventilation (the supply of air) fails to supply the perfused region. In other words, the ventilation/perfusion ratio (the ratio of air reaching the alveoli to blood perfusing them) is zero.〔 〕 A pulmonary shunt often occurs when the alveoli fill with fluid, causing parts of the lung to be unventilated although they are still perfused. Intrapulmonary shunting is the main cause of hypoxemia (inadequate blood oxygen) in pulmonary edema and conditions such as pneumonia in which the lungs become consolidated.〔 The shunt fraction is the percentage of blood put out by the heart that is not completely oxygenated. In pathological conditions such as pulmonary contusion, the shunt fraction is significantly greater and even breathing 100% oxygen does not fully oxygenate the blood.〔 ==Anatomical shunt== A small degree of shunt is normal and may be described as an 'anatomical shunt'. Anatomical shunting occurs when too much of the blood supplying the lung tissues via the bronchial arteries is being returned via the pulmonary veins without undergoing gas exchange. In addition, some of the coronary veins drain directly into the left ventricle of the human heart. This is why the arterial PO2 is slightly lower than the alveolar PO2. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「pulmonary shunt」の詳細全文を読む スポンサード リンク
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