Doctor's use a sphygnomnometer to measure your blood pressure. This device uses an inflatable cuff which fastens around the arm.

Pressure is defined as the force per unit area a fluid applies on its container it’s a basic physical measurement used in many areas an industries, plumber’s measure water pressure, mechanics tyre pressure, doctor blood pressure. Because of this (and the prevalence of metrification) there are many units, methods and equipment for measuring the pressure of a fluid.

Your doctor and other in the medical profession employ a device called a sphygnomanometer which will be calibrated in units know as millimetres of mercury, one of the many ways of precisely and scientifically stating the pressure of a fluid.

A Sphygnomanometer

Doctors measure blood pressure is measure units called millimetres of mercury, I’ll skip the science lesson about pressure units here just note that the gauge on a sphygmomanometer is calibrated in millimeters of mercury.

By inflating a cuff around the arm a precise and measurable amount of pressure can be applied to the arm and to the arteries and veins lying under the skin. By listening with a stethoscope a doctor can hear the hearts pulse in the vein and tell whether the vein is open or closed. By expanding the cuff until the vein closes and then listen for the pulse as the pressure on the vein is slowly released measurements can be made of the amount of pressure, the blood pressure, in the vein.

The heart is basically a pulsatory pump - that is it works by regular beating or pulsing squeezing blood around the body in regular pressure waves with the peak on the squeeze stroke and the low on the resting stroke. So in effect your heart produces two different pressures, a high one and a low one as it beats, these are called the systolic and diastolic pressures. A sphygmomanometer measures both of these so, for example,  a reading of 120/90 indicates a systolic (high) pressure of 120 mm of mercury and diastolic (low) pressure of 90 mm of mercury.

Through long observations and study doctors have a good understanding of what a normal range of blood pressure should be in an individual according to age, sex and other pre-existing conditions. As a diagnostic aid it is an invaluable sign.

It is a very good idea to records and track these daily readings in an spreadssheet - here is a Microsoft Excel spreadsheet to use as an example

Click to download here...