Hypertension and Hypotension : Part -1

Hypertension and Hypotension

We'll discuss about Hypertension and Hypotension in two different chapters. Today we'll discuss only about Hypertension. Hypotension will be discussed in next chapter.

I. Hypertension

Nearly 1 in 3 American adults has high blood pressure (hypertension). Once high blood pressure develops, it usually lasts a lifetime. The good news is that it can be treated and controlled.

Each time your heart beats, it pumps blood through the blood vessels, or arteries, that run through your body. Blood pressure is the force of the blood pushing against the walls of the arteries. Your blood pressure is at its highest when the heart beats, pumping the blood. This is called systolic pressure. When the heart is at rest, between beats, your blood pressure falls. This is the diastolic pressure.

Blood pressure is always given as these two numbers, the systolic and diastolic pressures. Both are important. Usually they are written one above or before the other, such as 120/80 mmHg (measured in millimeters of mercury, a unit for measuring pressure). When the two measurements are written down, the systolic pressure is the first or top number, and the diastolic pressure is the second or bottom number (for example, 120/80). If your blood pressure is 120/80, you say that it is "120 over 80."

Blood pressure changes during the day. It is lowest as you sleep and rises when you get up. It also can rise when you are excited, nervous, or active.

Still, for most of your waking hours, your blood pressure stays pretty much the same when you are sitting or standing still. That level should be lower than 120/80 mmHg. When the level stays high, 140/90 mmHg or higher, you have high blood pressure. With high blood pressure, the heart works harder, your arteries take a beating, and your chances of a stroke, heart attack, and kidney problems are greater.

A blood pressure reading below 120/80 mmHg is considered normal. In general, lower is better. However, blood pressure lower than 90/60 mmHg can be a cause for concern and should be checked out by a doctor.

Doctors classify blood pressures under 140/90 mmHg as either normal or prehypertension. If your blood pressure is in the prehypertension range, it is more likely that you will end up with high blood pressure unless you take action to prevent it.

Category	Systolic (top number)	Diastolic (bottom number)
Normal	Less than 120	Less than 80
Prehypertension	120-139	80-89
High blood pressure
Stage 1	140-159	90-99
Stage 2	160 or higher	100 or higher

When systolic and diastolic blood pressures fall into different categories, the higher category should be used to classify blood pressure level. For example, 160/80 mmHg would be stage 2 high blood pressure.

There is an exception to the above definition of high blood pressure. A blood pressure of 130/80 mmHg or higher is considered high blood pressure in people with diabetes and chronic kidney disease.

About two out of every three people over the age of 60 who have high blood pressure have isolated systolic hypertension. This means that only the top number, the systolic pressure, is high (140 mmHg or higher). Isolated systolic hypertension can be as harmful as when both numbers are high.

I.1 Symptoms and Diagnosis

High blood pressure is called the silent killer because it usually has no symptoms. Some people may not find out they have it until they have trouble with their heart, brain, or kidneys. When high blood pressure is not found and treated, it can cause:

• The heart to get larger, which may lead to heart failure.
• Small bulges (aneurysms) to form in blood vessels. Common locations are the main artery from the heart (aorta); arteries in the brain, legs, and intestines; and the artery leading to the spleen.
• Blood vessels in the kidney to narrow, which may cause kidney failure.
• Arteries throughout the body to "harden" faster, especially those in the heart, brain, kidneys, and legs. This can cause a heart attack, stroke, kidney failure, or amputation of part of the leg.
• Blood vessels in the eyes to burst or bleed, which may cause vision changes and can result in blindness.

The only way to find out if you have high blood pressure is to have your blood pressure measured. Blood pressure readings are usually taken when you are sitting or lying down and relaxed. Below are things you can do before getting your blood pressure taken:

• Do not drink coffee or smoke cigarettes 30 minutes before having your blood pressure taken.
• Wear short sleeves.
• Go to the bathroom before the reading. Having a full bladder can change your blood pressure reading.
• Sit for 5 minutes before the test.

Some people's blood pressure is high only when they visit the doctor's office. This condition is called white coat hypertension. If your doctor suspects this, you may be asked to check and record your blood pressure at home with a home monitor. Another way to check blood pressure away from the doctor's office is by using an ambulatory blood pressure monitor. This device is worn for 24 hours and can take blood pressure every 30 minutes. 

I.2 Causes

Hypertension can be divided into two types: essential (or primary) hypertension and secondary hypertension. If hypertension is caused by other diseases and the high blood pressure is gone after these diseases are cured, then the hypertension is the secondary hypertension. If hypertension is not caused by other diseases, it is the essential hypertension.

The causes of essential hypertension are not fully understood. However, it is known that salt plays an important role. Eating foods with more salt will increase the risk of developing hypertension. It also depends on the genes involved in processing salt intake. A more detailed explanation is given below.

Blood pressure = Cardiac output x Systemic vascular resistance

where the "cardiac output" is the blood volume pumped by the heart per minute and the "systemic vascular resistance" is the resistance of the blood vessels to blood flow. The two factors are regulated by complex systems such as renin-angiotensin-aldosterone system, baroreceptors, natriuretic peptides, kinin--kallikrein system, adrenergic receptor system, and others. However, the major pathway leading to essential hypertension is surprisingly simple. It turns out that salt plays the central role. 

The Major pathway to hypertension

When there is excess salt in the body, the blood volume increases, because the amount of water must increase to maintain plasma sodium concentration at a constant level. This is accomplished by two mechanisms: (1) Excess salt increases the osmolality of the body fluids, thereby stimulating the thirst center to make the person drink more water. (2) The increase in osmolality also causes the release of antidiuretic hormone, which makes the kidneys to reabsorb water before it is excreted as urine. Since the blood pressure is proportional to the cardiac output (and the blood volume), this explains why excess salt should increase the blood pressure.

In addition to the direct relationship with blood pressure, cardiac output can also affect blood pressure indirectly through "autoregulation". Higher cardiac output triggers autoregulation mechanism to constrict blood vessels all over the body. Increased vasoconstriction also raises blood pressure.

Kidney and salt

The amount of salt in the body is mainly controlled by kidneys, which filter over 170 liters of plasma containing 23 moles of sodium daily. More than 99 percent of the filtered sodium are reabsorbed at four locations: (1) the proximal tubule of the nephron (by Na+/H+ exchange), (2) the thick ascending loop of Henle (by Na-K-2Cl cotransport), (3) the distal convoluted tubule (by Na-Cl cotransport), and (4) the cortical collecting tubule (by epithelial sodium channels) (Figure). Gene mutations that increase salt reabsorption will raise blood pressure.

The epithelial sodium channels at the last location are tightly regulated by the renin-angiotensin-aldosterone system. Renin is an enzyme that can convert angiotensinogen into angiotensin I. The latter can further be converted into angiotensin II by angiotensin converting enzyme (ACE). Angiotensin I is inactive but angiotensin II can stimulate the secretion of aldosterone, which then binds to the mineralocorticoid receptor, triggering a series of events that lead to the increase of epithelial sodium channel activity. Higher sodium channel activity will increase salt reabsorption, thereby causing higher blood pressure. On the other hand, angiotensin II can cause blood vessels to constrict, which also increases blood pressure. Inhibition of ACE can prevent the production of angiotensin II, thus lowering blood pressure. ACE inhibitors have been widely used to control hypertension.

 I.3 Treatment

Some people can prevent or control high blood pressure by changing to healthier habits, such as:

• Following the DASH (Dietary Approaches to Stop Hypertension) Eating Plan, which includes cutting down on salt and sodium and eating healthy foods such as fruits, vegetables, and low-fat dairy products
• Losing excess weight and staying at a healthy weight
• Being physically active (for example, walking 30 minutes every day)
• Quitting smoking
• Limiting alcohol intake

Chocolate and Cocoa

Many studies have confirmed that chocolate and cocoa can lower blood pressure (reference). The major ingredient is flavonoid, which belongs to a group of compounds called polyphenols. Flavonoid is an antioxidant and also a vasodilator that enhances blood flow. Cocoa and dark chocolate (but not white or milk chocolate) are rich in flavonoid.

Medications

Sometimes it is necessary to add medicine to help lower blood pressure. Medicines will control blood pressure, but they cannot cure it. You will need to take blood pressure medicine for a long time.

Blood pressure medicines work in different ways to lower blood pressure. Often, two or more medicines work better than one. Some medicines lower blood pressure by removing extra fluid and salt from your body. Others affect blood pressure by slowing down the heartbeat or by relaxing and widening blood vessels.

Below are the types of medicine used to treat high blood pressure:

Diuretics are sometimes called water pills. They work by helping your kidneys flush excess water and salt from your body. This reduces the amount of fluid in your blood, and your blood pressure goes down. There are different types of diuretics. They are often used along with other high blood pressure medicines and may be combined with another medicine in one pill.

Beta blockers help your heart beat slower and with less force. Your heart pumps less blood through the blood vessels, and your blood pressure goes down.

Angiotensin converting enzyme (ACE) inhibitors keep your body from making a hormone called angiotensin II, which can increase blood pressure by (1) causing blood vessels to narrow and (2) causing salt reabsorption. By inhibiting the production of angiotensin II, blood pressure goes down.

Angiotensin II receptor blockers (ARBs) are newer blood pressure medicines that prevents the effects of angiotensin II by blocking its receptors.

Calcium channel blockers (CCBs) keep calcium from entering the muscle cells of your heart and blood vessels. This causes blood vessels to relax, and your blood pressure goes down.

Alpha blockers reduce nerve impulses that tighten blood vessels, allowing blood to pass more easily and causing blood pressure to go down.

Alpha-beta blockers reduce nerve impulses to blood vessels the same way alpha blockers do, but they also slow the heartbeat, as beta blockers do. As a result, blood pressure goes down.

Nervous system inhibitors relax blood vessels by controlling nerve impulses from the brain. This causes blood vessels to become wider and blood pressure to go down.

Vasodilators open blood vessels by directly relaxing the muscle in the vessel walls, causing blood pressure to go down.

It is important that you take your blood pressure medicine at the same time each day and not skip days or cut pills in half to save money. 

Hypertensive Crisis

Hypertensive crisis is a severe hypertension, with blood pressure above 180/120 mmHg. It is traditionally divided into urgency and emergency. The hypertensive urgency has the following symptoms

• Severe headache
• Shortness of breath
• Severe anxiety

Hypertensive urgency requires immediate medical treatment to lower blood pressure. Otherwise it may damage blood vessels and lead to stroke or other complications.

In hypertensive emergency, the severe hypertension is complicated by organ dysfunction, such as brain bleeding or heart attack. It requires hospitalization and intensive care.