这个因果关系我怎么看不懂？

Around 20% of UK adults aged 55 to 75 years have PAD, but only one- quarter have symptoms, usually intermittent claudication. Almost all PAD is because of atherosclerosis, and it shares the same risk factors as CAD. Some 5% to 10% of patients with PAD have diabetes, but this increases to 30% to 40% in those with severe limb ischaemia. The mechanism of PAD in diabetes is atheroma of medium to large arteries, so diabetes is not a contraindication to lower limb revascularisation.

约 20% 的 55 ～ 75 岁的英国成年人患有外周动脉疾病（peripheral arterial disease，PAD），但只有四分之一的人有症状，通常是间歇性跛行。绝大部分 PAD 都是因为动脉粥样硬化，和 CAD 的危险因素相同。5% ～ 10% 的外周动脉疾病患者患有糖尿病，但在肢体严重缺血的患者中，这一比例上升至 30% ～ 40%。糖尿病外周动脉疾病的机制是中大动脉粥样硬化，因此糖尿病不是下肢血运重建的禁忌证。

这个因果关系我怎么看不懂，下肢动脉算中动脉吗？