If someone w/vp shunt stands on head/bends downwards, is the pressure inside head same as those w/o vp shunt/hydro? Does it get more pressure? Faster?
Pressure. The shunt has a programmed pressure at which the valve will open therefore the pressure will not exceed that valve pressure. Repeated bending and standing may siphon the valve and allow a small excess of flow through the valve giving a headache that resolves when you lay down. Most have some sort of anti-siphon device but this may still occur.
Shunt keeps pressure. The shunt is designed to keep the CSF pressure at a steady level. Standing on your head is okay but why would one want to do so? Bending over, straining or lifting should not cause a significant rise in pressure and would likely be less of an increase than in people without a shunt (though the flow of CSF through the shunt is not the same dynamic two process as in non-shunted people).