Blood
Pressure
If the end of the hose is compressed, less air will get out. The hose will swell because the pressure inside it is higher -- air is coming in from the pump, but not going out again.
This happens in your blood vessels too.
If something closes off one of your arteries, it will be harder to push blood through and the artery between that point and the heart will have higher pressure in it.
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the 'Forward' link at the right to go on