The slave lies on a high bench, face up, ready for a ride ;-))
Isabella climbs on him, using his hands a a stair, then she sits down on his chest, you hear the air flushing out from his lungs, because her weight does a good squeezing job.
She moves slowly back lands on his throat, also a good place for sit, but then she lifts her ass and drops down on his face... air-supply is cut off.
She sits in various positions on his throat and face, mostly with her feet off the ground, means all her weight on him.