The ups and downs of high blood pressure:
What it all means
This simple measure, obtained
routinely on any doctor’s office visit, is often taken for granted
or misunderstood. Sure, it goes high and poses risk for heart
So what more is there to say?
But, take a closer look, and you realize that this boring, routine
measure really represents a phenomenal source of insight into heart
Anatomy of blood pressure
The heart squeezes, or contracts, at the start of
each heartbeat. Contraction lasts only a fraction of a second. Rapid
contraction forces about 90 cc of blood (about 1/3 cup) up, pushing
the aortic valve open, and blood passes up into the aorta and
rapidly distributes upward to the brain (via the carotid arteries on
either side of the neck), the arms, and downward to the abdomen,
pelvis, and legs. The force of heart contraction and its
distribution to the body is measured as systolic pressure, or the
top number in blood pressure.
As the 90 cc or so of ejected blood distributes rapidly throughout
the body, pressure in all the arteries drops over the ensuing half
second, and the aortic valve closes. This resting phase of blood
pressure is measured as diastolic pressure.
Unlike a river, which flows continuously downstream, blood flow is
pulsatile, with ebb and flow driven by pumping heart muscle. This
cycle repeats itself 60 or so times each minute, every time your
heart beats. Thus, blood pressure is the driving force within the
arteries of the body, literally the hydraulic pressure that drives
blood flow to all organs.
Just understanding these basic phenomena behind blood pressure
allows us to immediately surmise some ways blood pressure can show
evidence of dysfunction:
- If the volume of blood contained in the entire circulation is
increased (e.g., fluid retention resulting from excessive sodium in
the diet or poor kidney function), then the volume of blood ejected
from the heart increases and the entire network of arteries and
veins in the body are filled towards greater distention, raising
- If the volume of blood contained in the entire circulation is
decreased (e.g., dehydration, hemorrhage), then systolic pressure
will drop. This is hypotension, the opposite of hypertension.
- A factor that affects both systolic and diastolic pressure is the
flexibility, or “give,” of the arteries of the body. Soft, flexible
arteries expand with the increased blood volume of systole and relax
with diastole. Rigid arteries can’t accommodate the increased volume
of systole, nor relax with diastole; this is common in arteries
lined with semi-rigid atherosclerotic plaque (often appropriately
called “hardening of the arteries”) or with any condition that
simply adds rigidity to the artery walls.
- If the aortic valve is leaky, and blood flows backward back into
the heart during diastole, then diastolic pressure drops to abnormal
levels, e.g., 50 mmHg, indicating abnormally rapid distribution of
We require pressure sufficient to feed organs adequately and meet
their varied needs, including under conditions of increased demand
(e.g., walking on a treadmill, digesting dinner, sexual activity,
What we do not want is pressure so high that it scratches, scrapes,
and gouges the fine lining along the length of arteries. Repeated
injury leads to scarring, thickening, and, eventually,
With all that said, what is a normal blood pressure? What
combination of contractile systolic and relaxation diastolic
pressures represent an optimal balance between providing sufficient
flow yet not incurring damage? That may be among the most
contentious of questions. And what if what is widely regarded as
“normal” blood pressure is really high blood pressure?
What if “normal” blood pressure is really high blood pressure?
“Oh, no. I don’t have high blood pressure,” declared Ron after I
informed him that his pressure of 138/78 was on the high side. “Lots
of times I take it and it’s lower than that, like 120 or 130.”
Ron admitted that his primary care physician had told him for years
that his blood pressure had been “borderline” high, occasionally as
high as the 145/85 range. But other times it was lower, and Ron’s
reluctance to accept it led to a stalemate.
Unconvinced, we had Ron undergo some simple testing. A heart
ultrasound revealed several concerning findings: a overly muscular
heart muscle (left ventricular hypertrophy), an enlarged left atrium
(a risk for rhythm disorders like atrial fibrillation), and an
enlarged aorta (a risk for stroke and eventual aneurysm). Ron’s
blood sugar was modestly elevated, 112 mg/dl (pre-diabetes is
officially classified as 110 mg/dl or greater), and his creatinine
(a measure of kidney function) was mildly increased at 1.4,
signifying early kidney damage, likely from high blood pressure.
In other words, there was nothing “borderline” about Ron’s blood
pressure. If organs like the heart and kidneys showed evidence of
low-grade damage, it is much more than borderline. While occasional
blood pressures were indeed borderline, the net long-term effects
were clearly significantly negative.
At what point does blood pressure wreak damage and result in
long-term increased likelihood of death and cardiovascular
complications? A systolic pressure of 150? How about 140?
Many people are shocked to learn that measurable long-term
complications of blood pressure begin as low as a systolic pressure
of 115 mmHg. The large National Health and Education Survey, funded
by the National Institutes of Health (not funded by a drug company),
showed that systolic (top number) pressures of 115 or above are
sufficient to generate damage to arteries and other organs such
that, over several years, increased death and disease can be
measured (Prospective Studies Collaboration 2002). Every increment
in blood pressure of 20/10 doubles the risk of cardiovascular
The most recent national guidelines for blood pressure issued by the
National Health, Lung, and Blood Institute recommend maintaining
systolic blood pressure <120, diastolic <80 (<120/80), a substantial
change from the previous cut-off of 140/90. The new guidelines also
provide for a category called “pre-hypertension,” meaning blood
pressures of 120–139 systolic, 80–89 diastolic, that justify
lifestyle modification for improvement. (JNC VII 2003).
The above graphs are reproduced from the JNC VII (2003) report and
show how even “normal” blood pressure (gray line) of 120-129 mmHg
systolic, 80-84 mmHg diastolic is associated with increased
incidence of cardiovascular events; “optimal” blood pressure (red
line), defined here as <120/80, is associated with the least risk
for cardiovascular events. You can readily see that, by 10 years,
cardiovascular events are several-fold higher in people with “high
normal” (blue line) and “normal” blood pressure compared with
“optimal” blood pressures. The divergence is dramatic.
The recent release of the (Pfizer sponsored) Camelot Study conducted
by Dr. Steve Nissen of the Cleveland Clinic has fueled the argument
that blood pressure should be lower. In this study of nearly 2000
participants (all of whom had coronary heart disease), reducing
blood pressures from the “normal” range of 129/78 down to 124/76 led
to 31% (relative) reduction in heart attack, death, and
hospitalization. It also resulted in less atherosclerotic plaque
growth when arteries were examined with intracoronary ultrasound (Nissen
SE et al 2004). It’s irresistible to wonder what would have happened
had blood pressures been lowered to 100, and perhaps future clinical
trials will answer this question for us.
The message for those of us working hard to get as close as humanly
possible to eliminating heart disease risk, the message is clear:
Blood pressures (at rest) consistently <120/80 mmHg are necessary,
ideally 115/80 or less.
Get down and dirty with high blood pressure
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