Hey, that's cool! I've been taking kundalini yoga classes for one and a half year now and we've done this several times in different sets of poses. I've never learned a name for it so far, but now I know. *g*

If I remember correctly, this kind of breathing often features in yoga sets for balance, especially for the different parts of the brain. The only thing we've done differently is that we simply use the thumb and the index finger of our right hand to close our nostrils. I don't think it matters much, though.

I've experienced that once I've really myself fall into this pattern of breathing (because taking long and deep breaths is still one of the hardest things for me), it calms me a lot and makes me, well, very happy, too. :-)