Hypertension's Role in Heart Disease
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
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
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.