I don’t think that the cause of this is completely understood, but CO2 is a potent vasodilator. I’ve seen hatha yoga (physical yoga) practioners ditch hatha for prana-yoga (breath yoga) because they said it's a more powerful way to get to wherever yoga takes you.
http://www.health.harvard.edu/blog/stress-raising-your-blood...
I don’t think that the cause of this is completely understood, but CO2 is a potent vasodilator. I’ve seen hatha yoga (physical yoga) practioners ditch hatha for prana-yoga (breath yoga) because they said it's a more powerful way to get to wherever yoga takes you.