Blood pressure is the pressure by which the blood is circulated in the blood vessels of our body. The heart which is a muscular pump supplies the pressure to move the blood and also circulate the blood throughout the body. The blood vessels (in this case the arteries) have elastic walls and provide same resistance to the flow of blood. Hence, there is pressure in the system, even between heart beats.
“Nature’s purpose” in keeping blood pressure at a certain level is to ensure that the blood which carries oxygen and various nutrients needed by the body is pumped (i.e., the pressure of the blood in the arteries varies) from one blood vessel to another. It is the highest in the larger arteries and lower in smaller arteries. It is also different at different times of the day. It increases during physical exercises, walking, mental stress and also sexual activity, and decreases when the body is at rest during sleep.
The first measurements of blood pressure in human blood vessels were taken by inserting a tube into an artery, a somewhat dangerous and painful method. General use of blood pressure readings was made possible by the development of so-called ‘indirect techniques’, particularly an inflatable cuff like the tube in a tyre. The blood pressure is determined by inflating the cuff around a limb, usually the upper arm. One end of the stethoscope is placed over an artery ‘down stream’ to the cuff and the other end of the stethoscope is placed in the ears of the doctor observer. When the cuff pressure is greater than the blood pressure in the limb the blood cannot flow past the cuff and no pulse sounds can be heard. When the cuff pressure is just below the pressure level the blood can flow past the cuff again and the pulse sounds can be heard through the stethoscope.
The pressure at which the first pulse sound can be heard is called systolic blood pressure. As the blood pressure in the cuff is decreased the pulse sounds continue to be heard for a while and then they disappear again. The pressure level, when the sounds disappear, is the diastolic pressure. Blood pressure is usually indicated by two numbers. For example 130/80: 130, is systolic and the second number, 80, is the diastolic pressure expressed in millimetre of mercury (mm Hg).
Controlling your weight is a very important step that you can take to reduce your high blood pressure. Keeping your weight under control can also help you feel better, be more able to exercise, and reduce your chance of having a heart attack.
Two numbers are involved in a blood pressure reading. Both are important. The first of the two is your systolic pressure. This is the amount of pressure in your arteries when your heart contracts and releases blood into the aorta. The second number is your diastolic pressure. It tells how much pressure remains in your arteries between beats when your heart is relaxing and filling with blood. Your heart muscle must relax fully before it can contract again. During this time, your blood pressure decreases.
During systole (left), your heart muscle squeezes blood out of your heart’s pumping chambers (ventricles). Blood on the right side of your heart goes to your lungs and that on the left side is pumped into the large blood vessel (aorta) that feeds your arteries. During diastole(right), your heart muscle relaxes and expands to allow blood to flow into the pumping chambers from your heart’s holding chambers (atria).