The brain requires a constant supply of oxygen.

大脑需要持续的供氧。

《柯林斯英汉双解大词典》

Red cell mass, and thus oxygen-carrying capacity, remains constant over time in the healthy animal.

红细胞的数量和携带氧气的能力，在健康动物中时刻保持恒定。

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You may need to wear a device while sleeping that delivers a constant stream of air to your nostrils through a small hose, preventing the dangerous interruptions in oxygen.

那样的话你可能在睡觉时需要带一种设备通过软管向你的鼻孔里传送空气，以避免你呼吸暂停。

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She also needs a constant supply of oxygen.

BBC: NEWS | Health | Don't let baby die, pleads father

She had no firsthand knowledge of what it was like to feel your breath being squeezed off, to live in a world whose very atmosphere was a constant taunt, whose bountiful oxygen was as capriciously out of reach as a rainbow.

NPR: In 'Challenger Park,' Mom Is an Astronaut

The proportion of oxygen in the air 21% is constant whether at sea level or on the highest peak, but at lower altitudes there is more air pressure to force oxygen into tissue.

WSJ: Mayo Clinic Researchers on Everest Study High Altitude's Effects on the Body