It takes twice as much effort to breathe during sleep because of greater resistance to airflow in the airways and changes in the efficiency of the muscles used for breathing.
由于睡眠时呼吸道中的气流阻力更大，并且用于呼吸的肌肉效率有变化，所以在睡眠时呼吸需要用两倍的力气。
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A companion research effort looked at concepts for a new generation of supersonic transport aircraft capable of meeting NASA's noise, emissions and fuel efficiency goals for 2030.