Systolic and Diastolic Blood Pressures

I am sure we all know the standard blood pressure reading of “120 over 80” as the typical A-OK
measurement for normal. But I feel I’m not alone here, when it comes to truly understanding
what do these numbers really mean. The first number is referred to as the systolic measurement
and the second number is the diastolic measurement. Both parameters are expressed in
millimeters of mercury or mm Hg. As a reference, standard air pressure at sea level is 760 mm
Hg. So, both systolic and diastolic pressures are significantly less than “normal” atmospheric air
pressure.
Systolic is a Greek word meaning “a drawing together or a contraction.” It is the first beat heard
during blood pressure taking. It measures the maximum pressure within the blood vessels when
the heart contracts.

Diastolic is a Greek word meaning “drawing apart.” It is the last beat heard during blood
pressure taking. It measures the minimum pressure within blood vessels when the heart is
relaxed.

There are four chambers of the heart: right and left atrium and right and left ventricles. There are
two valves preventing blood from flowing in between the chambers. During the systolic phase
the ventricle and valve are closed and blood flows to the atrium. Once the atrium is filled with
blood, blood flows to the valve which will open, and the ventricle relaxes. Blood will then flow
from the atrium to the ventricle. The flowing and filling of the ventricles is known as the
diastolic phase.

Blood pressure is set by:
 cardiac output – the amount of blood pumped by each ventricle in one minute; and
 peripheral resistance – the resistance that the heart has to overcome to make the blood flow
through the blood vessels of your circulatory system.
According to the American Heart Association, the normal systolic pressure has a value ranging
from 90 to 120 mmHg. The normal diastolic pressure ranges from 60 to 80 mmHg. Anything
below or above these numbers would probably result in the occupational medical provider
requesting a consultation from your primary health physician. There is even a chance that until
this is done, our occupational health care provider may not sign the TPMC fit-for-duty form or
may sign the form while detailing some restrictions for your assigned work tasks.
Below is a chart that illustrates various measurements of blood pressure and how they are
interpreted as far as your cardiac health is concerned.

Blood Pressure Status

Systolic (mm Hg) IF Diastolic (mm Hg)
Min Max   Min Max

Normal Blood Pressure < 120 and <80

Pre-hypertension 120 139 or 80 89
Stage I High Blood Pressure (Hypertension) 140 159 or 90 99
Stage II High Blood Pressure (Hypertension) 160 180 or 100 110
Hypertensive crisis (where emergency care is
required) > 180 or >110

High blood pressure, or hypertension has been called the “silent killer”, because it often has no
warning signs or symptoms, and many people do not even know they have it. Over time, the
constant pressure overload causes accumulating damage that eventually becomes more than your
circulatory system can handle, often leading to serious health problems.

Around 5-10% of people have a specific underlying medical condition that causes a malfunction
in one or more of the physiological processes that maintain blood pressure; for example, chronic
kidney disease or thyroid disease. However, the majority of people with high blood pressure
have what is known as essential hypertension, meaning the cause is unknown.

Regardless of whether you have essential hypertension, or hypertension due to an underlying
condition, it can increase cardiac output, the resistance to blood flow caused by the muscle tone
and diameter of the blood vessels, known as peripheral resistance, or both. High blood pressure
is dangerous because the higher your blood pressure gets, the harder your heart has to work to
pump blood around your body, and the more likely your heart and blood vessels will be
damaged. Without treatment, hypertension can cause a heart attack, enlargement of your heart,
and/or heart failure. Your blood vessels may start to bulge, burst, or clog, and excessive pressure
inside the vessels in your brain may cause a brain bleed leading to a stroke. In some cases, high
blood pressure can also bring on kidney failure, blindness, and even cognitive impairment.
Obviously high blood pressure can cause some serious health conditions and if left ignored, we
could be playing a dangerous game of Russian Roulette. We are fortunate that, due to our work
assignments, our blood pressure is part of our mandatory physicals and therefore, do not need to
make a special appointment with our personal physician; it comes with the job. The only thing
we need to do is to recognize when our blood pressure falls outside of normal and then find out
what we can do to control this condition.

Good information is the best medicine.

Michael E. DeBakey (cardiac surgeon, Scientist and Medical Educator),