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Hypertension's Role in Heart Disease

By Cardiac Fitness Institute - London Health Science Centre - Ontario)
2003

Approximately 20% of people over the age of twenty develop hypertension during their lifetime - with the frequency increasing with age. If left untreated, hypertension can lead to stroke, myocardial infarction, also heart and kidney failure. Hopefully, the following discussion will help you to understand what hypertension is and the importance of treating it in the cardiac population.

During systole of the cardiac cycle, the contraction of the left ventricle causes a wave of blood to enter the aorta. This causes pressure within the entire arterial system - which is necessary to maintain a steady flow of blood to all other parts of the body until the next wave of blood. Hence, the crest of this wave is called the systolic blood pressure. At rest, this pressure generated by the heart is usually about 120 mm Hg. This number provides an estimate of the work by the heart and the strain against the arterial walls during the ventricular contraction.

At the end of each ventricular contraction there is a relaxation phase of the cardiac cycle called diastole. The arterial blood pressure here, after the crest of the wave has receded, is called the diastolic blood pressure. It usually decreases to about 70-80 mm Hg.This number provides an indication of peripheral resistance [ ie. back pressure ] - that is, it reflects the ease with which the " stored " blood flows from the aorta into the smallest blood vessels.

There is muscle surrounding the artery wall; tension in this miscle can cause hypertension. Generally speaking, hypertension is defined as having consistent systolic blood pressure over 140 mm. Hg and/or diastolic blood pressure above 85 mm. Hg. So, this lack of proper relaxation in the cardiac cycle causes the pump [ ie. the heart ] to have to work harder to supply the body with blood and oxygen. As a result over time, the muscle wall of the left ventricle thickens. As well, the lining of the arteries become damaged, making them more suseptible to cholesterol and plaque sticking to the their walls.

With exercise, there is a rise in the systolic and a levelling or slight decrease in diastolic blood pressure. Unfortunately, people who have chronic " above normal " blood pressure at rest also have chronic " above normal blood pressure when exercising. In the cardiac patient, this extra load on the heart may cause angina to occur earlier and more frequently.

Having said all this, in 90% of hypertension cases, the exact cause is unknown. What is known, is the course of available and effective treatment.

Non-pharmacological treatment of hypertension includes three main areas: 1.Weight reduction - it is thought that it reduces pressure by altering hormonal regulation of peripheral resistance. 2.Salt restriction - reduces pressure by reducing blood volume. 3. Regular aerobic exercise reduces pressure by lowering resting heart rate and is thought to alter certain hormonal effects on peripheral resistance. In addition, stopping smoking, reducing alcohol and caffeine intake can make minor reductions in pressure, by reducing heart rate.

Pharmalogical treatment includes: Beta-blockers, such as metoprolol, decrease heart rate and heart muscle contractility to ease the load. Diuretics, such as hydrochlorothiazide, reduce pressure by reducing total blood volume. Calcium channel blockers, such as diltiazem and ACE inhibitors, such as lisinopril, reduce pressure by vasodilation of the arteries, thereby reducing peripheral resistence.

In conclusion, effective treatment of hypertension , especially in the cardiac population, is essential to our short and long term health. Normal resting and exercise blood pressure help maximize our heart's ability as a pump. Our ability to exercise effectively will also be increased. Angina that may interfere with our daily lifestyle and exercise routine can be decreased. And finally, " controlled normal " blood pressure eliminates it as a risk factor for future cardiac events.

CCRF would like to thank London Health Science Centre - Cardiac Fitness Institute for their contribution to the website.

The articles, on the Cardiac Health Foundation of Canada website, are presented with the understanding that the Foundation is providing information only and not rendering medical advise. Please check with your family physician, specialist or health care professional before implementing any of the ideas expressed in these articles.

 
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