Blood pressures is the amount of blood pumped by the heart in relation to the size and condition of the arteries. Blood pressure is measured by the force of the blood on the walls of the arteries. Two forces contribute to blood pressure. One is the force of the heart as it pumps blood in the arteries and through the rest of the circulatory system. The other is the force of the arteries as they resist the blood flow.

Blood pressure is expressed as two numbers. The higher number, the systolic reading represents the pressure while the heart contracts to pump blood to the body. The lower number, the diastolic reading represents the pressure when the heart relaxes between beats. Blood pressure is usually measured in millimeters of mercury.

Blood pressure measurement is written as systolic pressure over diastolic pressure. In a blood pressure reading the systolic pressure is always stated first. For example, in their reading 120 over 80 the systolic reading is 120 and the diastolic is 80. Normal blood pressure is difficult to categorize because humans vary so greatly. Still, blood pressure below 120 over 80 is considered optimal for adults. A systolic pressure of 120 to 139 millimeters of mercury or a diastolic pressure of 80 to 80 millimeters of mercury is considered pre hypotensive and needs to be watched carefully. A blood pressure reading of 140 systolic over 90 diastolic or higher is considered elevated, high. This condition is also known as hypertension.


Blood pressure is measured by listening for Korotkoff sounds as the blood surges through the arteries. Korotkoff sounds are created when the inflated blood pressure cuff, which has temporarily stopped the flow of blood in an arm is deflated. This causes the blood to flow again and when it does turbulence can be heard as the blood begins to flow through the vein again. A stethoscope is used to listen to the brachial artery just under the cuff. While bleating the air from the cuff the point at which the first sound is heard is defined as the systolic pressure point. When the sounds disappear this is defined as the diastolic pressure point.

Patient variables that can influence blood pressure readings include:

  • Activity
  • Illness
  • Pain
  • Emotions
  • Medications
  • Alcohol Consumption
  • Temperature
  • Diet