Hypertension

The causes of high blood pressure

A comparison is often made between the bicycle tires and blood vessels to explain how blood pressure works in the body. Indeed, the air which presses against the inner wall of a bicycle tire keeps it inflated. Depending on the volume of air in the tire, it is full and ready to roll, or it is soft and seems "flat". Blood pressure is the force that blood exerts against the inner walls of blood vessels, like the air in the tire of a bicycle.

To measure blood pressure of a person, doctors take multiple readings using a blood pressure cuff (also called a sphygmomanometer). Blood pressure is expressed by two digits corresponding to a maximum value and the other to the minimum value (eg. 120 being the "top number" 70 and the "bottom number"). These two figures represent the pressure inside blood vessels when the heart contracts (systolic pressure - the highest number) and when the heart relaxes (diastolic pressure - the lowest figure).

Blood pressure is expressed in millimeters of mercury (mmHg). Blood pressure fluctuates throughout the day. It changes depending on time of day and according to the activities of a person and can go up during a stressful situation.