I think a valsalva maneuver keeps intra-thoracic pressure high by closing up a bit lower the air pathways? At least that is how I do it, it feels like it it bottled up at about the place my larynx site.

I see, so we're talking open vs closed glottis?

That makes more sense to me. An Open glottis definitely is more stimulating to the vagus nerve if nothing else so they are different.