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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 disease.
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 health

 

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 systolic pressure.
  • 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 blood.

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, etc.).

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, atherosclerosis.

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 disease.

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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