Blood pressure, balloons and hot water bottles

Physiologically, the formula to calculate pressure is force/area.

So if the force that is exerted over a constant area is doubled then the the pressure is doubled. If the force stays the same but the area is halved, the pressure will also double.

When we measure the blood pressure, we usually measure two values. So typically we get a measurement of 130/80. 130 is the systolic pressure. 80 is the diastolic pressure.

The Systolic blood pressure.
This is when the heart is pumping and ejecting blood into the vascular system and therefore is the highest