Blood pressure consists of two numbers. systolic pressure, the force exerted on the blood vessels when the heart beats, is the top number. Diastolic pressure, the force exerted when the heart is at rest, is at the bottom, in more ways than one. Systolic pressure gets the most attention from doctors and patients, says UAB cardiologist Jason Guichard, M.D., Ph.D.
“Physicians are busy people and, like it or not, they often focus on a single number,” Guichard said. “Systolic blood pressure is the focus, and diastolic pressure is almost completely ignored.” that’s a mistake, he argues. “Most of your arteries feed your organs during systole. but their coronary arteries are different; they’re surrounding the aortic valve, so they get blood only when the aortic valve closes, and that’s in diastole.”
Diastolic pressure has received more attention lately, however, thanks in part to an influential article on hypertension, written in 2011 by Guichard and Ali Ahmed, M.D., then a professor of medicine in the division of gerontology, geriatrics, and palliative care. of the uab and now the associate chief of staff for health and aging at the veterans affairs medical center in washington, d.c. (Ahmed is still an adjunct professor at the UAB.)
INFOGRAPHIC: See our quick guide to causes, and treatments, for low diastolic blood pressure.
That paper coined a new term, “isolated diastolic hypotension,” which refers to low diastolic blood pressure (less than 60 mm Hg) and normal systolic pressure (above 100 mm Hg). Older adults who fit those conditions are at higher risk of developing new-onset heart failure, the researchers found.
“High blood pressure is a problem, but low blood pressure is also a problem,” Guichard said. That understanding helped fuel a 2014 decision by panel members appointed to the Eighth Joint National Committee (JNC 8) to relax target blood pressure guidelines for people over 60. [Read Guichard’s take on “ideal blood pressure” and the new guidelines in this blog post.] “Years ago and until recently, doctors treated blood pressure so aggressively that many patients couldn’t even stand up. walk without getting dizzy,” guichard said. . “We want to empower patients to know that they don’t need to whittle those numbers down to nothing, to the point where they can’t play with their grandkids or play golf or take a simple walk around the block because their blood pressure is so low I think it’s important to raise awareness in this area, especially for older people.”
Jason GuichardAhmed and Guichard are continuing to explore the mechanisms behind low diastolic pressure in more detail. Several new papers are pending, Guichard says. In the meantime, he sat down with The Mix to explain the dangers associated with low blood pressure.
most people try to lower their blood pressure. what would you define as “too low” and why is it a problem?
A diastolic blood pressure between 90 and 60 is good for older people. once you start to drop below 60, that makes people uncomfortable. many older people with low diastolic pressure get tired or dizzy and have frequent falls. Obviously, none of this is good news for older people, who potentially have brittle bones and other problems.
Your coronary arteries are fed during the diastolic phase. if you have low diastolic pressure, it means you have low coronary blood pressure, and that means your heart will be starved of blood and oxygen. that’s what we call ischemia, and that kind of low-level chronic ischemia can weaken the heart over time, potentially leading to heart failure.
what could cause a person to have low diastolic blood pressure?
medicines are important. there are some medications that are to blame for lowering diastolic blood pressure more than systolic, specifically, a class of drugs called alpha-blockers, or centrally acting antihypertensive agents.
Another reason is age. As you age, your vessels get a little stiffer, and that tends to increase your systolic pressure and decrease your diastolic pressure.
it is difficult to reverse the aging process; but one potential therapy is to find ways to allow your vessels to retain their elasticity or, if they’ve lost it, perhaps ways to regain it.
The best current treatment is to reduce dietary salt intake, which has been shown to be closely related to vessel elasticity. the more salt you eat, the less elastic your glasses will be. most people’s salt intake is too high. Salt intake is a hotly debated topic in medicine, but most believe dietary salt intake of more than 4 grams per day is too high and less than 1.5 grams per day is too low. this depends on the person’s age and underlying medical problems, but this range is a good rule of thumb. There is some data that the ideal salt intake for healthy people is around 3.6 grams per day, but again this is hotly debated.
the uab hypertension group, directed by dr. Suzanne Oparil and Dr. David Calhoun has detailed much of the basic science showing the effect of salt at the molecular level on blood vessels. inside, its blood vessels are lined with a thin monolayer of endothelial cells. in an experimental setting, adding salt to these cells causes changes almost immediately. they become less reactive, which means they stiffen, and lose their elasticity, which is what is really seen clinically.
Also, vessel stiffness occurs very soon after taking a salt load during a meal, which is very interesting.
Beyond medication changes, what can people do to increase their diastolic pressure if it is too low?
Lifestyle changes, such as diet and exercise, can have immediate effects. your interior changes much faster than what the mirror shows you. Inside, you’re getting much healthier by eating better, exercising, managing your weight, and not smoking.
everyone thinks, “I’m going to have to do this for six months or a year before I see any change.” that is not true. the body is very dynamic. within a few weeks, you can see the benefits of the lifestyle change. in fact, with dietary changes in salt intake, you may see a difference in a day or two.
If someone has low diastolic pressure, what should they and their doctors look for?
If they’re not taking medications that we can adjust, the important thing is to monitor them closely; perhaps seeing a patient more often in the clinic and monitoring them closely for cardiovascular disease or symptoms of heart failure.
His original study on hypertension drew a lot of attention. what are you working on now?
We are finalizing some papers that address two major criticisms of that study. the first criticism was that we were looking strictly at, as the name suggests, isolated diastolic hypotension. We didn’t really care at the time what the systolic pressure was doing; but a high systolic pressure is a risk of heart failure, among other things. when we looked at the patients in our study, their systolic blood pressures were relatively normal and we adjusted for patients with a history of hypertension.
so we went back and redid the analysis, excluding people with hypertension altogether. and the results were still true. in fact, the association was even stronger.
The other review was about something called pulse pressure. that’s the difference between your systolic and diastolic blood pressure. and multiple studies have shown that an enlarged pulse pressure is also a risk factor for cardiovascular disease. some fellow researchers said, “really, all you’re seeing is just a broader pulse pressure. this is not necessarily new, it has been shown before.”
so we actually looked at the pulse pressure differences in all of these patients and broke them down by pulse pressure differences. and even when we adjusted the pulse pressure, the conclusion about low diastolic pressure was still true.
Actually, we look at three different sets of pulse pressure: normal, wide, and very wide. and it was true at all times. low diastolic blood pressure increased the risk of heart failure.
You are also interested in diastolic heart failure. what is that?
There are two different types of heart failure: one in which the heart’s pumping function is abnormal, known as systolic heart failure, and one in which the relaxation function is abnormal, known as diastolic heart failure. We have many medications and experience treating systolic heart failure, which is also called “heart failure with reduced ejection fraction,” from beta blockers, ace inhibitors, and arbs to mineralocorticoid receptor antagonists and statins.
diastolic heart failure, or “heart failure with preserved ejection fraction,” has no approved drug therapies to date. it was widely overlooked, to be honest, until about 10-15 years ago, when doctors realized that these poor patients had terrible symptoms of heart failure, but none of the classic objective measures of heart failure. In most cases, you can’t even tell the difference between a person with systolic and diastolic heart failure based on their symptoms. inside, however, his heart beats very well; the problem is that your heart is stiff, it doesn’t relax as well as it should. That stiffness causes fluid to build up in your lungs and extremities and causes many of the symptoms you have with systolic heart failure, but your heart’s pumping function is normal.
Now that there is awareness of diastolic heart failure, we realize that it is a very common problem. it seems that there are as many people with diastolic heart failure as with systolic heart failure. in fact, there may be even more people with diastolic heart failure.
Currently, it has become a well-studied form of heart failure. everyone is crying out for a drug to help these patients, because it is so prevalent, and they often have the same morbidity and mortality as people with systolic heart failure.
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