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肺循环系统有以下3个特征:①由于呼吸,肺泡同空气接触。血液在肺泡中充分氧合约需0.25S,而实际接触时间约0.75S,故时间充裕。但运动时心输出量增加,肺循环和体循环血等量增加,因此需肺泡构造不能与血液接触时间过分缩短。另外,在患肺炎等疾病时,肺泡不能提供充足的氧,若血液流经该部肺泡时,会因短路效应形成低氧血症。因此,在低氧区域内可见到肺血管出现不同于体血管的收缩反应(低氧性肺血管痉挛)。②与体循环相比,是低压系统。由于肺动脉压约为体血压的1/5,易受重力
Pulmonary circulatory system has the following three characteristics: ① due to breathing, alveolar air contact. Oxygenation of blood in the alveolar oxygen full 0.25S, while the actual contact time of about 0.75S, so plenty of time. However, cardiac output increased during exercise, pulmonary circulation and systemic blood volume increased, so the alveolar structure can not be shortened with the blood contact time. In addition, in diseases such as pneumonia, alveoli can not provide enough oxygen, if the blood flow through the alveoli, the formation of hypoxemia due to short-circuit effect. As a result, pulmonary vascular contractions (hypoxic pulmonary vasospasm), which are distinct from the systemic blood vessels, can be seen in the hypoxic region. ② compared with the systemic circulation, is a low-pressure system. As pulmonary artery pressure is about 1/5 of body pressure, susceptible to gravity