This results in cyanosis in the lower extremities, a blue or purple discoloration of the skin; that's the result of deoxygenated blood mixing with oxygenated blood.
When deoxygenated blood mixes into the systemic circulation, it'll often present as cyanosis, a bluish-purple discoloration of the skin, which can be seen in a baby within the first days after birth.
Coarctation of the aorta and a bicuspid aortic valve can cause lower extremity cyanosis, meaning a bluish or purplish discoloration of the lower limbs, and can result in congestive heart failure.
The increased CO2 levels in the blood can get so bad that some people develop cyanosis, which is a blue discoloration of the skin, and this is why patients with chronic bronchitis are sometimes referred to as blue bloaters.