慢性是因为急性？

Chronic rejection in the lung manifests itself as bronchiolitis obliterans syndrome, the origin of which is not clear, but which occurs in up to half of patients by 5 years posttransplant.Detection of chronic rejection is problematic, because in the early stages of acute rejection it is difficult to distinguish rejection from infection. Both conditions feature arterial hypoxaemia, pyrexia, leucocytosis, dyspnoea and reduced exercise capacity. These changes are followed by a decrease in diffusing capacity and FEV1, and later by perihilar infiltration or graft opacification on the chest radiograph. Bronchiolitis obliterans, as the name suggests, causes significant air-flow limitation; the FEV1 is used as a screening test and also to stage the degree of rejection.

肺移植慢性排斥反应表现为闭塞性细支气管炎综合征，其起源尚不清楚，但移植后5年内，多达一半的患者发生综合征。⁴⁸慢性排斥反应的检测是有问题的，因为在急性排斥反应的早期，很难区分排斥反应和感染，都表现为动脉低氧血症、发热、白细胞增多、呼吸困难和运动能力下降，随后是肺弥散能力和FEV1下降，然后胸片可见肺门周围浸润或移植肺磨玻璃样改变。闭塞性毛细支气管炎，顾名思义，会导致明显的气流限制，FEV1既用作筛选试验，也用于排斥程度的分期。

the origin起源？怪怪的，能不能认为是病因？

Detection of chronic rejection is problematic？慢性排斥反应的检测是有问题的？啥意思？慢性排斥反应的识别很困难？

Detection of chronic rejection is problematic, because in the early stages of acute rejection it is difficult to distinguish rejection from infection. 慢性排斥反应的检测是有问题的，因为在急性排斥反应的早期，很难区分排斥反应和感染？因为急性排斥反应与感染很难区分，就说慢性排斥反应的检测是有问题的？有这种因果关系吗？