Tren is a vaso-constrictor. to make a long story short, it diminishes the area of air exchange between your lungs and bloodstream. So u actually get less oxygen into your body each time you breath. ( Its the oposite of those pumps ppl use when they have asthma, to increase O2 intake)
Thats why u need to increase the breathing,(while on tren) to have the same amount of O2 comming in. This is where the tren cough comes from also. Upon injection, a higher concentration of tren reaches the lung alveoles, making it very hard to breath, untill the tren disolves into your bloodstream...
Ppl will react to tren differently, it will affect some ppl more then others. Some ppl are more sensible then others to medecine. I guess product purity/concentrations also play a role...