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Introduction to Hypertension

Hypertension aka High Blood Pressure

Blood pressure is defined as the pressure exerted by the blood against the artery walls.

Hypertension is one of the risk factors that has been correlated to and causative of many other human diseases.

Normal blood pressure is ~120/80 mmHg, hypertension in stage 1 is 140-159/90-99 and hypertension in stage 2 is 160+/100+.

Changes that Occur in Blood Pressure

Blood pressure can be determined by a formula:
Blood Pressure = Cardiac Output x Peripheral Resistance

In general terms blood pressure here is defined as the amount of blood exiting the heart and the amount of resistance it receives travelling through the body.

Cardiac Output = stroke volume x heart rate. The stroke volume is the amount of blood that leaves the left ventricle in one beat and heart rate is the amount of beats per minute. This gives you the amount of blood leaving the heart in one minute.

Peripheral Resistance is the amount of resistance the blood meets when travelling through the body. There are 3 categories of resistance: 1) blood vessel diameter, 2) blood viscosity, and 3) blood vessel length.

1) Blood Vessel Diameter: Since the blood is being pushed all at once through the blood vessels the room it has to move in impacts the resistance it meets (as well as the elasticity or ability of the vessels to stretch). When the vessel is larger then more blood passes through at once, this leaves a lower blood pressure, but when the vessel is too small to accommodate the blood then the pressure on the vessel rises.
The size of the vessel can be changed by the nervous system, hormones, chemicals and acid-base imbalances by controlling the smooth muscle tissue within the arteries/arterioles, and sphincters which control blood flow.

2) Blood Viscosity: Viscosity is simply the thickness of the fluid (blood). When the blood is thicker it is harder for particles (like plasma proteins) to flow past each other within the given vessel diameter. Therefore when the blood is thicker the pressure on the vessel is higher.

3) Blood Vessel Length: The longer a route is for the blood the pass through the body the more resistance the blood meets along the way, this causes an increased blood pressure. Fat and cancer cells create and require more blood vessels in order to function appropriately, these will increase the blood pressure since the path back to the heart is longer.

Measuring Blood Pressure

Blood pressure is measured with a sphygmomanometer (cuff that goes around the arm with a pressure gauge and pump) when the pressure on the arm is released the user must listen with a stethoscope to hear the rhythmic heart beat. The first normal beat you hear is the systolic pressure and the last normal beat you hear is the diastolic pressure.

If you don’t have any equipment available here is a tip to know a guideline of blood pressures in adults:
Carotid pulse: systolic of ~40mmHg.
Brachial pulse: systolic of ~60mmHg.
Radial pulse: systolic of >80mmHg.
Femoral pulse: systolic of ~80mmHg.

Causes of Hypertension

Some of the risk factors for hypertension include: heredity, age, race, insulin resistance, metabolic abnormalities, high salt intake, obesity, excessive alcohol consumption and low potassium dietary intake.

Heredity: Statistics show that there is a hereditary link in hypertension but research has shown that hypertension is not caused by one specific gene but many.

Age: Hypertension increases with age, and may appear later in life in patients that previously had normal blood pressure.

Race: Statistics show that African Americans have a higher prevalence of hypertension and earlier onset.

Insulin resistance: means that there is a higher amount of glucose (sugar) in the blood which causes the viscosity to increase resulting in hypertension.

High salt intake: There is a common saying that water flows where the sodium goes, if there is a high amount of sodium-salt in the diet then more water will be retained in the blood (increased viscosity) which leads to hypertension.

Obesity: causes insulin resistance (viscosity again) and a possible increase in aldosterone production, as well as increased adipose (fat) tissue which requires more capillaries (increase vessel length).

Excessive alcohol intake: effects blood pressure when it is 3 or more drinks daily, but the cause is unknown.

Potassium levels: have only been correlated with sodium intake (generally people that consume more potassium consume less sodium). Therefore, low potassium means more sodium, which means more water and greater viscosity.

As you can see from the above, some factors can be eliminated through lifestyle choices and others cannot.

Organ Damage

Hypertension causes/leads to the following organ damage:
a) Heart: left ventricular hypertrophy, angina or prior myocardial infarction, prior coronary revascularization, heart failure.
b) Brain: stroke or TIA
c) Chronic kidney disease
d) Peripheral vascular disease
e) Retinopathy

Recommended Read

A research paper detailing the increasing incidence of hypertension in Canada.
http://www.cmaj.ca/content/178/11/1429.full.pdf+html

Sources

1. Porth, Carol, Glenn Matfin, and Carol Porth. Pathophysiology: Concepts of Altered Health States. Philadelphia, PA: Wolters Kluwer Health/Lippincott Williams & Wilkins, 2009. Print.

2. National Heart, Lung and Blood Institute. (2003). The seventh report of the National Committee on Detection, Evaluation, and Treatment of High Blood Pressure. Publication no. 03-5233. Bethesda, MD: National Institutes of Health.

 

 

 

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2 Responses to Introduction to Hypertension

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