Blood pressure (BP) is the pressure exerted by circulating blood upon the walls of blood vessels, and is one of the principal vital signs. When used without further specification, “blood pressure” usually refers to the arterial pressure of the systemic circulation. During each heartbeat, BP varies between a maximum (systolic) and a minimum (diastolic) pressure.
The mean BP, due to pumping by the heart and resistance to flow in blood vessels, decreases as the circulating blood moves away from the heart through arteries. Blood pressure drops most rapidly along the small arteries and arterioles, and continues to decrease as the blood moves through the capillaries and back to the heart through veins.Gravity, valves in veins, and pumping from contraction of skeletal muscles, are some other influences on BP at various places in the body.Blood pressure is continually changing depending on activity, temperature, diet, emotional state, posture, physical state, and medication use.
Types of Blood Pressure
There are two types of blood pressure: Systolic blood pressure refers to the pressure inside your arteries when your heart is pumping; diastolic pressure is the pressure inside your arteries when your heart is resting between beats.
When your arteries are healthy and dilated, blood flows easily and your heart doesn’t have to work too hard. But when your arteries are too narrow or stiff, blood pressure rises, the heart gets overworked, and arteries can become damaged.
How Is Blood Pressure Measured?
Blood pressure is usually measured while you are seated with your arm resting on a table. Your arm should be slightly bent so that it is at the same level as your heart. The upper arm should be bare, with your sleeve comfortably rolled up.
Blood pressure readings are measured in millimeters of mercury (mmHg) and usually given as 2 numbers. For example, 110 over 70 (written as 110/70).
- The top number is the systolic blood pressure reading. It represents the maximum pressure exerted when the heart contracts.
- The bottom number is the diastolic blood pressure reading. It represents the pressure in the arteries when the heart is at rest.
To obtain your blood pressure measurement, your health care provider will wrap the blood pressure cuff snugly around your upper arm, positioning it so that the lower edge of the cuff is 1 inch above the bend of the elbow.
The health care provider will locate the large artery on the inside of the elbow by feeling for the pulse and will place the head of the stethoscope over this artery, below the cuff. It should not rub the cuff or any clothing because these noises may block out the pulse sounds. Correct positioning of the stethoscope is important to get an accurate recording.
Your health care provider will close the valve on the rubber inflating bulb and then will squeeze it rapidly to inflate the cuff until the dial or column of mercury reads 30 mmHg higher than the usual systolic pressure. If the usual systolic pressure is unknown, the cuff is inflated to 210 mmHg.
Next, the valve is opened slightly, allowing the pressure to fall gradually (2 to 3 mmHg per second). As the pressure falls, the level on the dial or mercury tube at which the pulsing is first heard is recorded. This is the systolic pressure.
As the air continues to be let out, the sounds will disappear. The point at which the sound disappears is recorded. This is the diastolic pressure (the lowest amount of pressure in the arteries as the heart rests).
What is Normal Blood Pressure?
Blood pressure is measured using two numbers. An example of this could be ‘the blood pressure is 120 over 80′, which is written as ’120/80mmHg’.
- The first figure is the systolic blood pressure – the maximum pressure in the arteries when the heart contracts (beats) and pushes blood out into the body.
- The second figure is the diastolic blood pressure. This is the minimum pressure in the arteries between beats when the heart relaxes to fill with blood.
Because the height of a mercury column is used in blood pressure gauges, standard blood pressure readings are always written as so many ‘millimetres of mercury’, which is abbreviated to ‘mmHg’.
The systolic pressure is always listed first, then the diastolic pressure. A typical normal blood pressure reading would be 120/80 mmHg.