What is blood pressure

There are two numbers in a blood pressure reading, the systolic blood pressure and the diastolic blood pressure.  Systolic blood pressure is the top number in the blood pressure reading.  A normal systolic blood pressure is between 90-140 mm Hg.  Diastolic blood pressure is the bottom number in the blood pressure reading.  A normal diastolic blood pressure is between 60-90 mm Hg.  

Blood pressure is measured by using an instrument called a sphygmomanometer (a blood pressure cuff) and a stethoscope.  The blood pressure cuff is placed snuggly around the upper arm. A stethoscope is placed over the brachial artery to listen to the blood pressure.  As the cuff is inflated, it increases the compression over the brachial artery until the blood flow through the artery is cut off, at which point the pulse wave will not be heard.  After the cuff is inflated, the air is then released and the first Korotkoff sound is heard which indicates the systolic blood pressure and when blood starts flowing through the arteries again.  After finding the systolic blood pressure, the cuff is still slowly deflated until no more sounds are heard.  The last Korotkoff sound that is heard or becomes muffled is the diastolic blood pressure. 

Hypertension and hypotension are conditions that are the result of abnormal blood pressures that can increase risk of a cardiovascular event.  Hypertension is generally classified as a blood pressure of greater 140/90 mmHg and hypotension is generally classified as a blood pressure of less that 90/60.