What is blood pressure?

Blood pressure is the pressure in the blood due to the beating heart. There are two types of blood pressure: systolic and diastolic. The systolic blood pressure corresponds to the pressure of the blood when the heart has imparted the maximum pressure. The diastolic blood pressure is the pressure when the heart is in the resting phase.

Why measure blood pressure?

High blood pressure is a very common condition in modern society. It has been estimated that one in five Americans, around 50 million people, suffer from high blood pressure. In general more men than women have high blood pressure, and the number of sufferers of both genders increases rapidly with age.

In around 5% of cases of high blood pressure is caused by kidney problems, but the causes of the other 95% of cases are unknown. There are a number of factors such as race, age, obesity, stress, smoking and lack of exercise that can contribute to the likelihood of a person developing high blood pressure but usually no one cause is directly responsible.

The majority of people with high blood pressure experience no symptoms, but if left untreated high blood pressure can lead to major health problems. Consequently the monitoring of blood pressure is vitally important in order to detect cases of high blood pressure and treat them early before health problems can develop.

Prolonged high blood pressure damages the lining of artery walls, making them thick and stiff. This condition is known as arteriosclerosis. Cholesterol is more likely to cling to the damaged artery walls, narrowing the arteries and thus preventing the blood from flowing through the body properly.

The heart has to work harder to compensate for the narrowed arteries. Over time this causes the heart to thicken and stretch, eventually failing to function normally, and causing fluids to back up into the lungs.

If the heart cannot work hard enough to compensate for the narrowing of the arteries then less blood can get around the body. Reduced blood flow to the heart can cause chest pain and angina, and eventually the flow may be stopped completely, causing a heart attack.

The function of the kidneys is to filter waste from the blood, but if blood flow to them is reduced then they become less efficient and waste builds up in the blood. Eventually they may fail completely, and dialysis or a kidney transplant will be required.

High blood pressure can also lead to brain damage and impaired vision. If a blood clot occurs in one of the narrowed arteries leading to the brain a thrombotic stroke may occur. Alternatively the weakened blood vessels in the brain may break due to the high pressure leading to hemorrhagic stroke.

A 25-year study of 11,000 individuals has confirmed that young men with high blood pressure are more likely to die from heart disease or other causes than those with normal blood pressure, translating to an estimated shorter life expectancy of two to four years.

The researchers called for increased population-wide prevention of increased blood pressure through healthy lifestyle habits and efforts to detect rising blood pressure in children, teenagers and young adults so that control of blood pressure can be started early.

How blood pressure is measured?

The non-invasive ausculatory method is one of the most common ways of monitoring a patient's blood pressure. The subject sits down and rests their arm on a table so the brachial artery is level with the heart. This is important when monitoring blood pressure, as pressure is proportional to height ( Δp = ρgΔh ). For example, if one measures the blood pressure at head height, the systolic/diastolic pressure readings will be approximately 35mmHg less compared to readings taken at heart level, whereas at ground height the pressure readings will be 100mmHg greater. A sphygmomanometer cuff is wrapped around the subject's upper arm, just above the elbow and a stethoscope is placed on the hollow of the elbow, over the brachial artery as shown below.

The cuff is 'pumped- up' to a pressure of 180mmHg, compressing the brachial artery hence causing the artery to collapse once the systolic pressure (the maximum pressure exerted by the blood against the wall of the brachial artery when the heart beats) has been exceeded. At the point where the pressure of the cuff is greater then the systolic pressure, the artery has collapsed thus, there is no flow of blood through the brachial artery.

The valve on the pump is loosened slowly to allow the pressure of the sphygmomanometer cuff to decrease. Once the systolic pressure is reached (approximately 120mmHg in the 'normal' case), the brachial artery opens causing volatile blood flow, which cause vibrations against the artery walls. These noises are called Korotkoff sounds (named after their discoverer) and can be heard through a stethoscope as the pressure exerted onto the brachial artery falls. The blood flow through the brachial artery increases steadily, until the pressure of the sphygmomanometer cuff falls below the diastolic pressure (the pressure between successive heart beats, the low pressure), approximately 80mmHg. This is the point where the blood flow through the artery is laminar.

The Korotkoff sounds

The Korotkoff sounds are the sounds heard through the stethoscope as the pressure cuff deflates. The sounds are first heard when the cuff pressure equals the systolic pressure, and cease to be heard once the cuff has deflated past the diastolic pressure.

It is generally accepted that there are five phases of Korotkoff sounds. Each phase is characterised by the volume and quality of sound heard. The figure below illustrates these phases. In this example, the systolic and diastolic pressures are 120mmHg and 80mmHg respectively.

Phase 1

With the pressure cuff inflated to beyond the systolic pressure, the artery is completely occluded and no blood can flow through it. Consequently, no sounds are heard above the systolic pressure. At the point where cuff pressure equals the systolic pressure, a sharp tapping sound is heard. We recall that the blood pressure oscillates between systolic and diastolic pressure. At systolic, the pressure is great enough to force the artery walls open and for blood to spurt through. As the pressure dips to diastolic, however, the artery walls bang shut again. It is the closing shut of the artery walls that results in the tapping sound.

Phase 2

This phase is characterized by a swishing sound, caused by the swirling currents in the blood as the flow through the artery increases. Sometimes, if the cuff is deflated too slowly, the sounds vanish temporarily. This happens when the blood vessels beneath the cuff become congested, and is often a sign of hypertension. The congestion eventually clears, and sounds resume. The intervening period is called the auscultatory gap.

Phase 3

In this phase, there is a resumption of crisp tapping sounds, similar to those heard in phase 1. At this stage, the increased flow of blood is pounding against the artery walls.

Phase 4

At this point, there is an abrupt muffling of sound. The blood flow is becoming less turbulent. Some medical practitioners choose to record this point as the diastolic pressure.

Phase 5

This is the point at which sounds cease to be heard all together. The blood flow has returned to normal and is now laminar. The pressure cuff is deflated entirely and removed.

Definition of High blood pressure

Also known as hypertension, high blood pressure is, by definition, a repeatedly elevated blood pressure exceeding 140 over 90 mmHg -- a systolic pressure above 140 with a diastolic pressure above 90.

Chronic hypertension is a "silent" condition. Stealthy as a cat, it can cause blood vessel changes in the back of the eye (retina), abnormal thickening of the heart muscle, kidney failure, and brain damage.

For diagnosis, there is no substitute for measurement of blood pressure. Not having your blood pressure checked (or checking it yourself) is an invitation to hypertension.

No specific cause for hypertension is found in 95% of cases.

Wait for the next article from me where we be going through treatment options and natural ways of prevention, to save your medical bills

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