Isabella: How long?

Isabella want to know, how long her slave can hold his breath under her ass. In te beginning it's a nice test to have Isabella's round and soft ass on the face, but the breath-holding times get longer, he cannot be without air and begiins to struggle. This is  what Isabell loves, to have a struggling slave under her ass for riding out. Soon she streches her legs and sits fullweight on the poor (or happy) slave.