"Dead air" or dead space is the volume of air that fills the space from your mouth/nose to the small airways of your lung that exchange oxygen and carbon dioxide. An above average height man may breath about 600 ml per breath and have about 200 ml be dead space. So only 400 ml air available for exchange. If he closed his nose and put is mouth around a large straw that held 600 ml of volume, he'd have to increase his breathing depth (and frequency) compensate, and would get pretty tired.
The OP likely just learned about dead space ventilation and the giraffe is a logical follow up question.
tbiko t1_j42emtg wrote
Reply to comment by NimdokBennyandAM in How do giraffes breathe? by NimishApte
"Dead air" or dead space is the volume of air that fills the space from your mouth/nose to the small airways of your lung that exchange oxygen and carbon dioxide. An above average height man may breath about 600 ml per breath and have about 200 ml be dead space. So only 400 ml air available for exchange. If he closed his nose and put is mouth around a large straw that held 600 ml of volume, he'd have to increase his breathing depth (and frequency) compensate, and would get pretty tired.
The OP likely just learned about dead space ventilation and the giraffe is a logical follow up question.