<prompt> Percentage of Normal dead space is:-50-7020-Oct30-4080-90  <response>: Dead space - Some of the air a person breathes never reaches the gas exchange areas but simply fills respiratory passages where gas exchange does not occur, such as the nose, pharynx trachea. - The air is called dead space air because its not useful for gas exchange. - Normal tidal volume 500 m - Normal dead space 150 m Thus, Normal dead space ratio 30 - 40 