In my experiences, I've never encountered shortness of breath from either compound! In fact, Clen is a bronchiodilator - an asthma medication who's function is to open airways. It does spike your heartrate, thus the fat burning effects of the medication.
As for Tren, I've used it during cutting phases while doing tons of cardio and never expereinced shortness of breath. Tren is a perfect compound for use while cutting, so I assume most people may be in some cutting-sort-of-phase while using it and therefore are doing cardio as well.
Both compounds' sides are dose-related, so simply make certain you're at teh right dosage and you'll by happy.