什么叫“呼吸急促干预前”？谢谢

Cardiorespiratory Disease

Patients with cardiovascular or respiratory disease have poor exercise tolerance for three main reasons. First, the ventilatory response to exercise is more rapid, so a greater minute volume is required to achieve a given V o2. Second, the proportion of MBC that a patient can tolerate is reduced, and when combined with the previous observation this results in an extreme limitation of exercise tolerance before shortness of breath intervenes. Hypoxia or hypercapnia occur more commonly during exercise in patients with respiratory disease. Third, a limited increase in cardiac output in response to exercise means that mixed venous oxygen levels will fall to low levels more quickly, and also causes inadequate muscle blood flow, impairing the function of respiratory and other muscles. Anaerobic metabolism therefore occurs much more quickly, leading to extra ventilatory requirements and exhaustion.

心肺疾病

心血管或呼吸系统疾病患者的运动耐力差，主要有三个原因。首先，运动兴奋通气更快，这是因为机体需要更大的分钟通气量来达到特定的的O₂。其次，运动时，患者可耐受MBC的程度降低，结合之前的观察结果，这导致在出现呼吸急促前就已达到运动耐受性的极限。呼吸系统疾病患者在运动时更易出现低氧血症或高碳酸血症。再次，运动时心排血量的增加有限，意味着混合静脉血氧水平将更快下降到更低水平，这会导致肌肉血液循环不足，损害呼吸系统和其他肌肉的功能。因此，更快发生无氧代谢，又加重了通气需求和衰竭。

各位老师，帮我看一下，什么叫“呼吸急促干预前”？谢谢