breathe _verb 

ADVERBS

deeply
・She breathed deeply in the cool night air.

heavily, hard 
・He was breathing hard by the time he reached the top of the hill.

fast, rapidly
・I noticed that Freddie was breathing rapidly just before he fainted.

slowly
・Breathe slowly and try to relax.

softly, gently
・His wife lay next to him, breathing softly.

steadily, evenly, regularly
・He forced himself to breathe steadily and remain calm.

normally, properly
・The patient said that he felt a sharp pain in his chest and was unable to breathe normally.

easily
・Sucking a mint may help you breathe more easily when you have a cold.

NOUNS

air 
・It was wonderful to be outside and breathe some fresh air.

fumes 
・These children are breathing traffic fumes all day long.

ADVERBS

in 
・It felt good to breathe in some country air.

out 
・Breathe out slowly, and relax.

PHRASES

can/cannot breathe
・He held her so tight that she could not breathe.

can hardly breathe
・It was so hot that I felt as though I could hardly breathe.

breathe through your nose/mouth
・This cold makes it hard to breathe through my nose.
・Whales breathe through a blowhole in the top of their head.

have trouble/difficulty breathing, struggle to breathe 
・In high altitudes some people have trouble breathing.
・The crowd pressed in around me and I struggled to breathe.