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They call it “The Silent Killer.”

That’s because most people feel nothing, even when the condition is relatively severe. Many people don’t even know they have it. But left untreated, this monster can cause untold damage to tissues and organs all over the body--particularly the heart, kidneys, and brain.

Those are important.

I’m talking about hypertension, or high blood pressure. Without treatment, it can be devastating. But when diagnosed and treated properly, it can be well-controlled and compatible with a long, vigorous, productive life. Hypertension may be silent and sneaky, but it’s not at all unmanageable.

The first step is to know our enemy.

Your cardiovascular system is really just a series of pumps and pipes that, well, circulates your blood throughout your body.

The circulation of the blood allows you to oxygenate the blood and fill it with nutrients and hormones and other yummy stuff, deliver that yummy stuff to your tissues, pick up the carbon dioxide and reaction products and “exhaust” generated by your cellular engines, and deliver all that gunk to appropriate waste disposal systems--notably your lungs for the CO2 and your kidneys for the other stuff.

The pump is obviously the heart, and as most of us have known since we were, like, 5, the pipes are the arteries, veins, and capillaries. And like any system of pump and pipes, our circulatory system has a bunch of pressure gradients to make the blood go round and round.

The pressure on the lung side, or the pulmonary circulation, is pretty low overall, and we won’t talk about that much today.

The other side of our circulation is the systemic circulation, or everything else.

The pressure in the veins, which bring blood back to the right side of the heart from the tissues, is relatively low.

But the pressure on the left side of the heart, which pumps blood to our organs and tissues, is much higher, as is the pressure in the arterial tree, which carries that fresh, oxygenated, nutrient-rich red blood. The pressure in the arteries, and their smaller branches, the arterioles, has to be high, so that all that good stuff can penetrate the tissues and keep you going.

But sometimes, the pressure in the arterial tree can get too high, and that’s not good. That’s hypertension.

But clinicians and academic bodies like numbers, and most clinicians will define hypertension as a sustained, resting systolic blood pressure of 140 mmHg or greater, or a resting diastolic blood pressure of 90 mmHg or greater. Remember that most people think of a resting blood pressure of 120/80 as being normal, although some authorities think even this level of blood pressure promotes some degree of cardiovascular disease.

Diagnosis depends on separate measurements at least a month apart with good equipment under specific conditions. It’s not the kind of thing you can diagnose with one visit to the ER for a sprained ankle or a ride in one of those blood pressure measuring chairs at the drugstore. The most accurate approach seems to be 24-hour ambulatory blood pressure monitoring.

Hypertension comes in multiple flavors. For example, there’s pulmonary hypertension, which is high blood pressure in the lung-side, or right-sided circulation.

That’s not as common, and it’s kind of a different thing, so we’re not going to talk about it here.

We’re interested in the far more common arterial hypertension, and we can divide that into two types, primary and secondary.

Secondary hypertension is high blood pressure that’s caused by another identifiable pathology. For example, a tumor of the adrenal glands, called a pheochromocytoma, can cause high blood pressure, among other problems. When the tumor is removed, the hypertension goes away. Thyroid disease, problems with kidney circulation, structural disease of the aorta--all can cause secondary hypertension.

Primary hypertension, also called essential hypertension, is far, far more common. About 90-95% of cases of high blood pressure are primary in nature. Primary hypertension may afflict as many as 1 billion people worldwide, and probably affects about 35% of the adult population of North America. The risk goes up with age, male sex, low socioeconomic status, and in African-Americans. From 1997 to 2007, the number of deaths from hypertension increased by 35%.

And here’s the real kicker: Up to 20% or more of those with the condition don't even know they have it. And that’s bad.

So what’s going on here? What causes this? Well,

The two factors that contribute to the pressure in the arterial tree are: (1) the cardiac output, or the amount of blood the heart pumps per unit time, and (2) the resistance of the arterial tree, or what physiologists call the total peripheral resistance, or TPR.

Of the two, the second factor, TPR, is what’s most important in chronic hypertension, and it’s determined by changes in the small arteries and the arterioles.

See, these small arteries and arterioles aren’t just passive pieces of biological PVC pipe that sit there while blood flows by. They’re active structures.

Arterioles are the smallest branching level of artery before the capillaries, and they have muscular walls that can relax or contract, causing the pressure inside them--and in the capillary bed--to go up or down. This gives your body a lot of control over the perfusion of various capillary beds, so that you can increase the circulation in some tissues and organs while decreasing it in others, as the situation demands.

These muscular arterioles are regulated by input from the autonomic nervous system, which controls and integrates so much of your physiology, and also from various hormones. They also respond to local tissue concentrations of various chemicals like oxygen, carbon dioxide, nitrous oxide, and the acid concentration or pH.

In essential hypertension, one or more underlying mechanisms causes sustained, abnormal, harmful constriction of the arterioles, increasing the blood pressure. These mechanisms include genetic factors, and there does seem to be a form of inheritance. But there doesn’t seem to be a single genetic variant that causes high blood pressure in most people with the disease, which leads many scientist to think that most primary hypertension is multifactorial.

Changes in the sympathetic nervous system seem to play a role in essential hypertension. This is the fight or flight side of the autonomic nervous system, which increases both arterial resistance and heart rate. Chronic stress can lead to over-activation of the sympathetic system and help promote high blood pressure, and there may be a genetic component making some people and populations more sensitive to this over-activation.

Some authors have suggested that an imbalance between dietary sodium and dietary potassium may play a role in the development of hypertension, by causing excessive contraction of the smooth muscle cells in the arteriolar walls. This is an ongoing area of investigation, but it’s a good reminder to eat your fruits and vegetables and show a little restraint with the salt shaker.

Finally, dysfunction of the renin-angiotensin-aldosterone system appears to be important.

This is a complex hormonal system responsible for helping us maintain fluid balance, blood pressure, and blood pressure, but it can get out of whack. When it does, it produces inappropriate levels of angiotensin and aldosterone.

Angiotensin tells blood vessels to contract more, increasing blood pressure, and aldosterone causes us to hang on to fluid and salt, thereby increasing the volume of blood in the system and further contributing to blood pressure, not to mention other nasty effects like edema or swelling.

The ultimate consequence is a level of pressure inside the arteries, arterioles and capillaries that pounds at you with every heartbeat.

High blood pressure, if untreated, damages the endothelium, or delicate lining of blood vessels, leading to atherosclerosis, which in turn puts us at risk for heart attack, stroke, and many other horrible complications.

The heart, which has to push against this elevated blood pressure, beat after beat, day after day, year after year, will eventually begin to change in structure and function, and will eventually not be able to keep up--that’s heart failure, and it’s as bad as it sounds.

Damage to the small vessels of the brain promotes various kinds of stroke and neurodegeneration. Damage to small vessels of the retina leads to hypertensive retinopathy and possible visual loss. The constant pounding of the capillary beds and fine structures of the kidney leads to hypertensive nephropathy, kidney failure, and ultimately dialysis, which is no fun.

And while they are uncommon, there are a few hypertension related catastrophes that we see in emergency medicine more often than we’d like, such as hypertensive encephalopathy, in which high blood pressure causes coma and seizures, intracranial hemorrhage, or bleeding into the brain, and aortic dissection, which causes a massive tear and unzipping of the biggest artery in your body.

We hate that.

The bastard of it is that while most of this damage is going on, YOU FEEL NOTHING. High blood pressure pounds at capillary beds throughout your body, but aside from maybe some fatigue or an occasional bout of dizziness, you’re asymptomatic. This is why it’s so important for you, the athlete of aging, to get regular checkups and make sure this monster isn't’ sneaking up on you.

That’s because mild hypertension or, better yet, a mild prehypertensive state, can often be treated very effectively with lifestyle modification alone--diet, exercise, stress reduction, and so on. The effect of these changes on hypertension in particular will vary from person to person, as they vary from study to study, but the effect of these interventions on your health in general will be nothing but positive.

And even if you turn out to have full-blown high blood pressure requiring medical intervention, the addition of a carefully selected antihypertensive agent to these lifestyle modifications can be lifesaving, and enable you to get on with a happy, healthy, active life.

We’ll talk more about these very important, very commonly used medicines in our next episode. I hope you’ll join us then.

Thanks for watching this episode of Greysteel. Our content is offered for ejumacational and infotainment purposes only, and is not presented as medical advice for any particular person, patient, disease or condition. If you have questions about your health, you should work closely with your physician.

I’d like to thank my friends and colleagues, Doctors Austin Baraki and Phil Lewalski, for their helpful comments on this episode.

A big shout out to our patrons on Patreon. If you would like to join them and help Greysteel make more videos like this, you can go to Patreon.com/greysteel and become a patron. Or if you just want to make sure you don’t miss any more free content about healthy aging, go to YouTube.com/greysteel and subscribe to our channel. That really helps us out, too. Until next time, stay strong, and stay healthy.