Hypertension has long been recognized as a risk factor for premature heart disease, along with other factors such as family history, diabetes, high cholesterol, smoking, obesity, and sedentary lifestyles. The traditional normal adult blood pressure has been considered to be 120/80, but recent studies have suggested that this value may no longer be true.
First, let’s define the terms. The systolic value is the top number. It represents the maximum pressure being generated as the heart forces blood out of the ventricle into the arteries with each heartbeat. The diastolic value is the bottom number and represents the resting pressure between heartbeats. The difference in these two numbers is called the pulse pressure. A person with a blood pressure of 120/80 has a systolic value of 120, a diastolic value of 80, and a pulse pressure of 40 (120 minus 80).
To understand the pulse pressure, it is important to realize that the aorta, the major artery coming out of the heart, acts like a huge “shock absorber” by stretching or “giving” a little with each stroke of the heart and muting the pressure transferred into the rest of the system. Other arteries have the same ability to dilate or constrict to help regulate the pressure in the peripheral system. When the arteries are healthy, this results in the “normal” pulse pressure of about 40 (e.g., if for a BP of 120/80, 120 – 80 = 40). Unfortunately, degenerative changes over time related to smoking (carbon monoxide injury), diabetes mellitus, excess fatty acids (cholesterol, triglycerides), and other factors result in scarring, stiffening, and narrowing of the aorta and other arteries. This is commonly known as atherosclerosis or “hardening of the arteries.” As this process continues, the arteries become less able to absorb the pressure wave generated with each heartbeat, so more of that pressure is transmitted downstream and is manifested by higher systolic values, higher diastolic values, and wider pulse pressures – e.g., hypertension. (There are also other causes of hypertension beyond the scope of this discussion.)
Historically, we have believed that the diastolic value was the most important indicator of cardiovascular disease and made our decisions accordingly. The following table lists the previous generally accepted guidelines:
Systolic (top number)
60 – abnormal and potentially dangerous
61-90 – low
91-130 – normal
130-150 – Moderately elevated
>150 – high
Diastolic (bottom number)
<40 – dangerous due to decreased tissue perfusion
41-60 - low
61-90 - normal
91-100 - borderline
>100 - high
The recent studies I mentioned above noted a correlation between high systolic blood pressure and wide pulse pressures (greater than 40) with heart disease. This led to a push for more aggressive control of the systolic value and less emphasis on the diastolic value. While I wholeheartedly agree with the benefit of maintaining the most normal blood pressure possible, I believe the recent studies reached inaccurate conclusions. They assert that “systolic hypertension” causes the heart disease. I believe cardiovascular disease is already present and causes the elevated systolic readings and widening pulse pressures. In a sense, it becomes an academic argument because the BP needs controlling either way to reduce the risk of further unnecessary damage to the cardiovascular system.
Based on this new view, there is an effort to redefine “normal” BP to something more like 100/60, and to consider 120/80 as “pre-hypertensive” because a substantial number of people with 120/80 readings will progress to have hypertension later in life. I disagree with the underlying premise and believe 120/80 is still normal, but it certainly wise for each of us to take appropriate measures to preserve that normal value through proper lifestyle. Family history is the single most important indicator for premature heart disease, and you can’t do anything about that. Thankfully, other factors are more easily impacted. You certainly can work on your weight, exercise, improve your cholesterol, control your blood sugar if you have diabetes, and avoid smoking. Medications can help keep your blood pressure in the best possible range if it does start to rise despite your best non-pharmacological efforts.
My frustration with what I consider to be erroneous conclusions in the recent studies mentioned above motivated me to write an article poking fun at some of today’s “scientific studies.” This article was published in Family Practice Management, one of our family practice journals, in 2004. It can be viewed at http://www.aafp.org/fpm/20041100/editorial.html. I hope you enjoy it.
Thomas L. Horton, MD