Blood pressure is represented by a pair of numbers that most people can quote. It may come as a surprise that the reason the blood pressure is what it is is largely unknown. That, however, hardly deters the medical profession from applying a panoply of procedures to lower it.
Giraffes have a systolic (the larger number of the pair) blood pressure as high as 300 mmHg. It needs to be high in order to get blood to the brain, which is 7 or 8 feet above the heart. This means the blood vessels in the lower extremities have to withstand a pressure that would rupture ours. A lot of evolution went on to keep that giraffe’s brain well supplied with blood.
Our brains are about 18 inches above our hearts, so we can get by with lower pressures. For a healthy person, the systolic (high) number tends to be between 110 and 120. This is a resting condition. This same fit person can run her blood pressure up to 200 or more with intense exercise.
How does the body determine proper blood pressure?
As central as this measurement is to prescribing assorted meds and procedures, the actual mechanisms and how they interact to control blood pressure are not fully understood. In fact, they are widely misunderstood.
At rest, the brain is the dominant energy guzzler, and our healthy person needs 120 to keep it perking along. Our intense exerciser’s high temporary pressure is obviously there to fulfill the needs of her muscles and lungs. So demand is one side of the equation. Suppose with the onset of the middle-age spare tire, the blood pressure creeps up as well. What is to be done about that?
Blood pressure is high—is the body getting it wrong?
There are many factors involved in blood pressure regulation. The body will control it by varying the heart rate and by varying the constriction of the blood vessels. The constriction is a clever idea. It can open up some areas and tighten up others. This enables the body to distribute blood where it is needed: to the gut after a meal, to the muscles when exercising, etc. Let us consider our middle aged “patient” with the 140 systolic pressure. Here is the interesting bit: Even though the blood pressure is elevated, that person’s body still has full control. He can lower his heart rate, he can relax his blood vessels. His body can set it wherever it wants. If his body deliberately sets it at 140, is that “right”? Or should the medical profession work their magic and force it back to 120? What if it is at 150 or 160 or 180?
Among other things, the body is clearly regulating the pressure at whatever number it deems necessary to keep the brain supplied. There are sensors in the carotid (neck) arteries that sense this. If they are thwarted via some drug or gadgetry, the pressure drops.
The body increased the pressure for a reason. It was necessary because the arteries have more resistance, or the endothelium (blood vessel lining) is in poor shape, or both. The body, left to its own devices, will supply the brain with blood, even if the pressure has to go up and up.
You might ask, “If the body is so smart, why does it let some people’s blood pressure get to 180?” This is a good question, because there seems to be no dispute that 180 is too high, despite what the brain may want. At that level, blood vessels could pop (an aneurysm). Unlike the giraffe, we never evolved anything to deal with blood pressures that high, and for a simple reason: there was no need for it. Until the advent of the Western lifestyle, with its physical indolence and excess gorging of starches, no blood pressures ever got that high. In fact, they never got high at all. Among extant hunter-gatherer tribes today, heart disease is very rare, and blood pressures are all an enviable 110/50. So high blood pressure, like sugar/starch overload, is something new, and our body reacts to it poorly.
So when should modern medicine intervene?
Since modern medicine doesn’t fully understand why the body wants the blood pressure where it is, there is a wide range of philosophies on intervention. We like the Mayo Clinic guidelines. Here is what they have to say:
- If your blood pressure is below 120/80, there is nothing to fix.
- If above 120/80, but below 140/90, it’s “Pre-hypertension,” and drugs are not recommended.
- Above that, but below 160/100, it’s “Stage 1 Hypertension.” Try to reduce it with a lifestyle change and failing that, consider drugs.
- Above that, do a lifestyle change and “discuss” taking medication with your doctor.
As far as drugs go, the Mayo Clinic doesn’t seem to be in any hurry to pull the trigger. Why then are so many doctors writing endless prescriptions for hypertension? Here, Mayo is perhaps reflecting more recent research, which appears to rather sharply limit the groups of people that benefit from any known drug. Most of the drugs, singly or in combination, do not appear to lower all-cause mortality for most groups, and for some combinations, there is an increase in death rate.
How should they intervene?
This is the money question, in more ways than one. Unfortunately, most interventions don’t work. Many make things worse.
Beta-blockers. These inhibit adrenalin production and slow the heart down. This lowers blood pressure, though it means less blood to critical areas such as the brain and muscles. Beta-blockers are commonly prescribed for even moderate hypertension, but have never been proven to be of benefit to any cohort. They increase mortality.
Calcium channel blockers. Blood pressure is controlled by the tension of the muscles surrounding the blood vessel walls. Calcium channel blockers relax these (and all other) muscles. Calcium channel blockers are frequently prescribed for hypertension. They have been found to also increase mortality and breast cancer risk.
ACE inhibitors. These also relax the muscles surrounding the vessels. For people with high blood pressure, these drugs show a slight decrease in all-cause mortality (~7%). This appears to be the only drug in the lot that actually shows any benefit (albeit a slight one).
Thiazide is a diuretic and causes the body to dump fluid. It also reduces blood pressure, though the reason for this isn’t known (after 60 years on the market). One serious side effect is adult onset diabetes.
Not such a promising list, is it? And it is by no means complete. Also once in vogue:
- Cut nerves to the kidney.
- Ablate (snip) certain areas in the limbic system regions of the brain.
- Cut nerves to the adrenals due to their role in the sympathetic system.
- Block kidney and/or lung-based angiotensin.
- Force sodium from the kidneys.
- Force water from the kidneys.
Finally, let us not forget statins, which don’t lower blood pressure at all. We will refrain from hectoring you about statins. There are numerous posts on this blog delving into this multibillion-dollar medical scam.
It’s the same old story: The body usually gets it right. Before meddling with a bodily function like blood pressure or cholesterol levels, the practitioner should ask why things are as they are? Could there be important reasons? In almost all cases there are.
For you medical do-it-yourselfers wishing to measure you own blood pressure…
The wrist devices do not work very well. Don’t waste your money. Omron has a line of cuff type devices. You will often see these in doctor’s offices. The street price is around $70. They seem to work fine. And home based blood pressure numbers are far more reliable than any obtained at the doctor’s office. Trust those over any numbers obtained at your doctor, dentist, or opthamologist’s office.