Why does holding the valsalva maneuver cause syncope?

Syncope is the fancy doctor's term for ping out. The valsalva maneuver increases the pressure inside your chest. This can collapse the big veins returning blood from your body back to your heart. If your heart isn't getting any blood, it can't send oxygenated blood to your brain. When your brain is deprived of oxygen, you p out. In a healty person, ping out will cause you to stop holding the pressure and blood will flow to your heart. If you have diseased blood vessels that are less flexible, they don't bounce back to being open as easily. In those cirstances, holding the valsalva maneuver can be dangerous and potentially fatal.