This reduces the amount of oxygen that reaches the organs of the body.

VOA: special.2009.07.14

The respiratory system plays an important role in maintaining our internal environment at the proper level of oxygen, by bringing the right amount in.

呼吸系统的重要性在于,通过向体内输入适量的氧气,维持人体内环境中的氧平衡

耶鲁公开课 - 生物医学工程探索课程节选

At about nineteen-thousand meters, the air is so thin and the amount of oxygen so small that a person needs a lot of special equipment to survive.

VOA: special.2011.04.06

This makes it more difficult for the body to effectively use the same amount of oxygen as it would on the ground.

VOA: special.2009.07.14