Management of Hypertension
In this chapter we would be cross examining and discussing the medical condition “High blood Pressure” for easy understanding to even the non-medical personnel.
What is high blood pressure?
High blood pressure also popularly known as hypertension by way of definition is simply an increase in the force at which blood is pushed against the walls of the arteries as it moves through the body. Breaking this further down, it is important to note that throughout the body that is from your head to the sole of your feet there are vessels which help to carry blood to vital organs in the body. These vessels can be likened to “tubes” as we can relate with tubes carrying water likewise these vessels enable the flow of blood.
There are three main vessels in the body namely:
- The Arteries: Which have thick muscular walls with elastic stretch and recoil to enable blood flow evenly with less resistance. They usually carry blood away from the heart to other parts of the body.
- The Veins: These are large blood vessels which convey blood back to the heart unlike the arteries the veins have thin walls and do not stretch or recoil in the same way as the artery therefore they do not work under pressure.
- The Capillaries: These are the smallest blood vessels that connect arterioles (really small arteries) to venules (really small veins) to enable the exchange of water, oxygen, carbon dioxide and many other nutrients between the blood and the surrounding tissues. These small vessels also do not work under pressure.
So when it comes to high blood pressure our main concern are the arteries in the body and the rate at which blood flows through them. Remember I mentioned that the arteries take blood away from the heart to other parts of the body which Include the brain and the kidneys (These are very vital organs that need optimum supply of blood). Therefore any increase in the blood pressure of the arteries supplying these organs may lead to damage of these organs which would be discussed later in the chapter.
Blood Pressure Values
We would all agree that in order to say something is high or low we need to have cut off values. The blood pressure reading usually consists of two values. The first is known as the systolic blood pressure (SBP) and the second is known as the Diastolic blood pressure (DBP). We would get to the meaning of both SBP & DBP shortly, but for now, it is important to know the meaning of the various blood pressure readings our doctors get after appropriate / accurate measurement.
The questions are what are the ideal values? How do we know if we have values that indicate hypertension? To answer these questions, the normal values of blood pressure at birth is around 90 (SBP) / 60 (DBP) but as we grow older it gradually rises to about 110/70 – 120/80 (SBP / DBP). This is not to say when the blood pressure is checked it must be 110 / 70 or 120 / 80 for it to be considered normal. What is being said is that it is usually around this range of values that it is considered normal. For example, people with values ranging 115 / 76 mmHg, 120/72 mmHg, 112/80 mmHg are all considered normal. This brings us to the classification of blood pressure for adults. There are four categories involved as shown in the table below.
|Category||SBP (mmHg)||DBP (mmHg)|
|Prehypertension||121-139||81 – 89|
|Stage 1 HBP||140-159||90 – 99|
|Stage 2 HBP||>160||>100|
For clarification purposes, pre hypertension is blood pressure that is higher than normal but not high enough to be called high blood pressure hypertension. It basically is a warning sign of hypertension.
Stage 1 hypertension (moderate) and stage 2 hypertension (Severe)
Now that we know the classification of blood pressure for adults let us go into the meanings of SBP and DBP. To understand this terminology we have to know just exactly how the heart works.
How many of us know that the heart typically works like a pumping machine? Well yes the heart is a muscular organ that is responsible for pumping blood and oxygen to all parts of the body. It is located between the lungs in the chest cavity.
Below is a diagrammatic representation of how the heart works.
The heart is divided into four chambers. The left and right atria as well as the left and right ventricles as indicated in the diagram above. The right atrium receives blue blood (deoxygenated blood without oxygen) from the body through the vena cava (Big veins in the body i.e the superior & inferior vena cava. This blue blood in the right atrium is then delivered to the powerful lower chamber (Right ventricle) passively (without so much effort) but for this to happen, the tricuspid valve has to open up.
The right ventricle on the other hand pumps the oxygen poor blood that has been delivered to it into the lungs so that the blood can get oxygenated by the lungs before continuing its journey. This journey from the right ventricle to the lungs is made possible with the help of the “Pulmonary Artery” (Remember we discussed arteries previously and we said they carry blood away from the heart? Here we can see it carrying blood away from the right ventricle of the heart to the lungs). The pulmonary artery also has a valve that opens up to allow the entry of blood.
Now the blood has been oxygenated? So what next?
The oxygenated blood is then carried back to the left atrium via the pulmonary vein. The blood now in the left atrium is then delivered to the left ventricle through the bicuspid valve (which must also be open at this time).
From the left ventricle the blood is forcefully pushed into the aorta (A very large artery) which also has a valve that must open for the blood to flow easily the blood in the aorta is then distributed to the body so that absorption of nutrients and oxygen from the blood can take place.
The deoxygenated blood is then returned from the body back to the heart and the cycle is started again.
NB: It is important to note that we have mentioned four valves so far in the cardiac cycle. The first two are
- The Tricuspid & Bicuspid valves (located just below the atrium).
- The pulmonary valve & aortic valve
These valves are very essential to prevent the back flow of blood.
Wow! That was a really exciting insight to how the heart works right? This then brings us back to the meanings of systolic blood pressure and Diastolic blood pressure.
Systolic blood pressure is the pressure required to push blood from both the ventricles into the respective arteries (Pulmonary artery & Aorta). At this moment the heart is said to be in systole.
Diastolic blood pressure on the other hand is the pressure in the arteries when the heart fills with blood and gets oxygen.
Types of Hypertension
There are two main types of hypertension
- Primary Hypertension
- Secondary Hypertension
Primary hypertension (also known as essential hypertension) usually has no single identifiable cause for the increase in blood pressure. This means there is no underlying disease or condition causing the high blood pressure. It is the most common type of hypertension. This hypertension may probably have been caused by unhealthy diet and lifestyle as well as genes.
Secondary hypertension which is less common is caused by specific disease conditions which may include kidney failure, tumours, sleep apena. Treatment of the underlying conditions would cause the hypertension to subside in most cases.
So Who is At risk of Hypertension?
Not to worry this would this would be extensively dealt with in chapter 3 of the hypertension chronicles. So the question is how does hypertension come about? This would take us to the pathophysiology of Hypertension
Physiology of Hypertension
What are those factors actually responsible for high blood pressure? This would involve a little mathematics if you don’t mind.
The simple formula
BP = CO X PR
BP= Blood Pressure
CO= Cardiac Output
PR= Peripheral Resistance
Wait a minute, before we delve into this formula we have to understand the individual factors which are “cardiac output” and “peripheral resistance” as they both contribute Into determining the blood pressure.
Cardiac output can be simply defined as the amount of blood the ventricles pump out of the heart per minute to the rest of the body. It could also be defined using this formula CO= HR X SV
Where HR is the number of heart beats per minute and SV is the amount of blood the ventricles pump out with each contraction. “Whew” I think it is safe to say the maths is over. So basically the summary of the mathematics is that any increase in cardiac output or peripheral resistance would most definitely lead to an increase in blood pressure.
The main cause or lets say the most sensitive factor is peripheral resistance. I am sure you might be wandering what peripheral resistance is??. Simply put, it is the amount of resistance to blood flow in the arteries majorly caused by arteriolar vasoconstriction (which simply means narrowing of the arteries).
Let us pause and think about this for a minute using diagrams. Assuming we have two tubes for the flow of water
Which of these 2 tubes above do you think would allow much more flow of blood with less pressure?
Well yes you guessed right, definitely tube 1 above. This is because it has a wider lumen. Likewise if for any reason the arteries in the body become narrower there is an increase in peripheral resistance which would definitely lead to an increase in blood pressure.
Before we go further, I would like to quickly mention the main reason for vaso constriction. So you see , we have a system in the body known as the “Autonomic Nervous system” which is responsible for regulating the body’s unconscious actions.
The autonomic nervous system is further divided into the sympathetic and parasympathetic nervous system. The sympathetic nervous system’s primary response is to stimulate the body’s fright or flight response while the parasympathetic nervous system stimulates the body to “feed and breed” and consequently to “rest and digest”. Various disorders can cause a dysfunction or over activity of the sympathetic nervous system such as “Pheochromolytoma”. This condition among other factors have the roles they play in leading to hypertension.
Apologies for the minor diversion, but I felt the need to explain this concept well. As earlier stated, any increase in peripheral resistance would majorly be caused by arteriolar vasoconstriction which narrows the lumen thereby leading to decreased blood flow to various important organs of the body.
The other organs do not have as much power to act on this reduced blood flow as the kidneys do. Oh No! The kidney must not go down without a fight right? Yes, to prevent this, a cycle is subsequently activated which would be diagrammatically represented before I go further with the explanation.
By way of explanation, a reduction in the blood flow to the kidneys would stimulate the release of an hormone called Renin (which is solely produced by the kidney). Renin release can then lead to pathways that eventually cause an increase in blood pressure. As in the diagram renin can stimulate another hormone to be released. This hormone known as angiotensinogen is in its inactive form.
Angiotensinogen is then converted to Angiotensin I which is acted on by an enzyme called Angiotensin converting enzyme to convert it to Angiotensin II. Angiotensin II is a potent vasoconstrictor and of course would lead to an increase in peripheral resistance as explained earlier which subsequently increases blood pressure.
On the other hand Renin production can also lead to the production of another hormone known as aldosterone. Aldosterone acts mainly on the kidneys and leads to sodium retention and of course when sodium is retained water follows therefore both sodium and water are being retained in the body and this would cause an increase in blood volume. When the blood volume increases, the cardiac output would also increase.
Remembering the formula for BP which is CO X PR. An increase in cardiac output would define increase the blood pressure.
Complications of High Blood Pressure.
It is important to know that a sustained increase in blood pressure has very serious consequences which may even be life threatening. We would be discussing some of these complications briefly.
Let’s begin. If high blood pressure is left untreated it can wreak havoc to three major organs of the body namely.
- The heart
- The kidney
- The brain
The heart: Hypertension is a major risk factor for hypertensive heart disease. This encompasses a group of complications namely coronary artery disease and heart failure. Remember the “Coronary Artery”. Yes it is the major artery that supplies blood to the heart. High blood pressure contributes to the thickening of the blood vessel walls and subsequently lead to coronary artery disease.
Heart failure is another condition that can occur as a result of high blood pressure as high blood pressure increases the heart’s workload which causes the heart muscle to thicken and causes the left ventricle to hypertrophy (increase in the volume of an organ or tissue due to the enlargement of its component cells). This hypertrophy would eventually lead to the heart failure (Do not let me bore you with medical jargons, moving on)
The kidneys and the circulatory system (blood vessels, heart) are all interconnected. The kidneys are full of arteries, and damage to those arteries can make the kidneys lose their ability to filter toxins in the blood as well as losing their various functions. So now we have established that high blood pressure can lead to damage of the kidneys right?
Apart from kidney failure, high blood pressure can also lead to stroke, which is a disease condition that affects the brain and is caused by a shortage of blood supply to the brain or bleeding into the brain from an aneurysm (rupture of a blood vessel).
I am sure we now understand fully the consequences of this deadly disease “Hypertension”. In our next series we would be discussing how to detect high blood pressure. Thanks for reading guys, cheers!