http://www.innerbody.com/anatomy/respiratory
At high intensity though? Surely the air doesn't have enough time to be warmed? Filtered I can agree with but warmed I doubt.
Obviously ΔT will be smaller at higher flow rates, but you're still going to get more warming through the nasal cavity than you will through the mouth.
@hippy started
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http://www.innerbody.com/anatomy/respiratory