from Jack Herer's The Emperor Wears No Clothes:
Marijuana smoke effectively dilates the airways of the lungs, the bronchi, opening them to allow more oxygen into the lungs. It is also the best natural dilator of the tiny airways of the lungs, the bronchial tubes - making cannabis the best overall bronchial dilator for 80% of the population (the remaining 20% sometimes show minor negative reactions).
Cannabis lowers blood pressure, dilates the arteries and reduces body temperature an average of one-half degree, thereby relieving stress.
Instead of smoking, vape it! Chances are good that it will increase your ability to breathe in more oxygen, plus allowing more of it to flow through your body via the dilated arteries. And since there have also been studies about cannabinoids boosting the immune system, that's even better.