下か行こう大だい動どう脈みゃく

Meanings

1

descending aorta

Anatomical term for the portion of the aorta that descends through the thorax and abdomen.

vein, pulse, hope

大だい動どう脈みゃく
大動脈 is the general term for the aorta; 下行大動脈 specifies the descending portion.
上じょう行こう大だい動どう脈みゃく
上行大動脈 is the ascending aorta, the opposite segment.

Compound of 下行 (descending) and 大動脈 (aorta), a direct anatomical calque.