Your body is made up of a circulatory system (blood vessels) that carries blood (oxygen and nutrients) to all the organs (brain, heart, liver, spleen, stomach, intestines, muscles, etc). The circulatory system is likened to a tree. The main tree trunk is the aorta (the biggest artery) and the branches are comparable to smaller vessels. A certain amount of force is required to keep the blood moving through the blood vessels. The amount of force that is exerted on the artery wall as blood flows through them is what we refer to as “blood pressure”.
Blood pressure is generated from the force of contraction from the heart pump. The final determinant of how much pressure is registered in the blood vessels is determined by the smallest branches called the arterioles. When the arterioles constrict, blood pressure is raised and when they dilate blood pressure is lowered.
Exactly how much blood pressure is needed varies with the body’s activities. When your heart beats faster the blood pressure rises to push out more blood with each beat. Conversely when the heart pumps slower, the blood pressure is lowered.
There are two measurements of your blood pressure. When your heart pumps to expel blood into the circulation, your blood pressure is higher (systolic blood pressure), when your heart relaxes to fill with blood, your blood pressure is lower (diastolic blood pressure).
Blood pressure is expressed in two sets of numbers – an upper bracket and a lower bracket as below:
Systolic pressure (the maximum force that is exerted on the blood vessel wall during a heartbeat)
Diastolic pressure (the amount of force exerted when the heart is resting momentarily between beats)
Blood pressure is normally measured at the brachial artery (a major artery in the upper arm).
Blood pressure is usually measured using an instrument called a sphygmomanometer (pronounced spig-moe-man-noe-meter) which consist of an inflatable rubber cuff, an air pump and a column of mercury or a dial or digital readout reflecting in an air column. The measuring unit is in millimetres of mercury (mmHg).
Persistently elevated blood pressure (called high blood pressure) is a significant risk factor for heart attacks and strokes.
Note that high blood pressure is often silent and itself does not usually cause symptoms so an affected individual may not be aware that he/she is at risk.