Swarup garu,
I was only referring a little part of what has been posted about the problems in pranayama and some yogasanas in detail here:
http://www.brchaitanya.org/saimasterforums/index.php?topic=948There were two diagrams that explain the problems with holding breath in the link given for shallow water blackout. I was referring only those which i think are appropriate for this section. It has nothing to do with swimming.
I was going through some of the messages and got the post on holding breath and thought I need to tell about problems with it else kids will attempt all those things.