What is Blood Pressure?

     Blood pressure is like the water pressure in your house. The major difference is that spigots in the house open the water to runoff. Unless you start bleeding, your plumbing is a closed system under constant pressure, with a pump at the center that keeps the blood moving through the pipes. The heart pumps blood into the aorta producing systolic pressure, the top number in your blood pressure measurement. This force pushes the blood through a progressively branching network of thick-walled, elastic arteries throughout the body – the arterial side of the circulatory ystem. The branches get smaller and smaller and beyond the smallest arteries, called arterioles, the pressure wave dissipates as the blood flows into a vast network of tiny, thin-walled capillaries, with diameters so small that microscopic red blood cells line up in single file to get through.  Press hard on one of your fingertips, enough to make the skin pale, and then let up and watch it grow pink again. You are watching a capillary network fill.

    In this capillary network, where pressure in the closed system is the lowest, all your cells exchange their waste products for fresh supplies of nutrients and oxygen. From capillaries, blood flows under low pressure into thin-walled veins and back to the heart. This is the venous side the circulatory system. Between heart beats, a time called diastole when the heart rests and blood pours into it from the venous system, the pressure in the arterial side of the system is at its lowest. This diastolic pressure in the arterial system is the bottom number in your blood pressure measurement.

        A house’s pipes are fixed in size and shape. The body’s plumbing is more sophisticated. The muscular walls of the arteries respond to signals from hormones and nerves, with dilatation and constriction necessary to shunt blood to locations where it is needed. When you have a full stomach, your limb muscles give up some of their blood supply (hence the old adage about not swimming right after eating). A good scare reverses this pattern, leaving the stomach queasy and preparing the muscles to fight or flee.  In cold environments, blood is shunted to vital organs in the head and torso at the expense of the skin and extremities – the reason that wearing a hat will keep your fingers warmer.

Blood pressure is thus a constantly changing measure of the force of blood flow within the arteries. It goes up with physical activity and comes down with rest. High or low, the pressure is a complex response to the demands placed on the body by activities, emotions, and environment. It is influenced by nutrition and hydration and other health factors. Genetic makeup, as always, plays a role and steers many people toward high blood pressure or hypertension, as they age.

In a small number of cases, hypertension is secondary – a response to an underlying problem (adrenal gland tumor, congenital abnormality of the aorta, narrowing of a renal artery, or genetic endocrine gland problem). In 95% of cases, hypertension is essential – a response to multiple factors that have in common an ability to increase resistance in the smallest arterioles, which forces the heart to pump blood under higher pressure.

Essential hypertension affects an estimated 70 million Americans. Repeated  resting blood pressure measurements,  over 140/90, without any evidence for an unusual cause, put a patient in this category (more recently some experts are recommending that the number be 130/80, but there is controversy over the subject). Over many years, blood pressures consistently above 140/90 cause slow “end-organ” damage – kidney failure, strokes, hardening of the arteries, retinal damage, and heart failure. The higher the blood pressure, the more the arteries thicken and harden, and the harder the heart has to pump to keep the blood flowing. The more the blood vessels change, the more likely they are to block blood flow, or to rupture, like corroded pipes in a house. And the more rigid they become, the worse the blood pressure gets, especially the systolic component.

How do you know if you have high blood pressure? Symptoms are rare until end organ damage is well underway, so you must depend on routine measurements, and sort out whether or not the anxiety produced by the measuring process is a culprit in raising the pressure. This sometimes means getting a home measuring device, or at least getting repeated checks in an environment away from a doctor’s office. Severe hypertension, with diastolic pressures of 140 or more, can produce headaches, dizziness and blurred vision and is a medical emergency – fortunately uncommon.

Of the numerous factors correlated with essential hypertension, age and family history are the most common and the least “treatable.” But the other common factors – inactivity, obesity, excessive salt intake (greater than 5.8 gms/day), lack of sleep, and excessive alcohol intake – help time accomplish its negative work. These factors, at least, are under some voluntary control, and the platform of treatment of essential hypertension is diet and exercise. For every 25 lbs of weight lost, blood pressure can drop about 3 points. Regular, vigorous aerobic exercise stimulates capillary expansion to accommodate the demand for blood by the nervous system and muscles.  Thirty to 45 minutes of daily aerobic exercise yields drops of 5-15 mm, and helps normalize weight. Removing the salt shaker from the kitchen and minimizing processed food drops daily salt intake.

Even with the best of lifestyles, anti-hypertensive medicines are sometimes necessary.  Each patient’s health picture determines the best options among the many available drugs. The mainstays of treatment affect the kidney hormones renin and angiotensin (ACE inhibitors), or block the effects of the autonomic nervous system (beta blockers), or help the kidneys release more salt (diuretics). Very often, combinations of two or even three drugs work better than one alone.

Because hypertension produces no symptoms, and its consequences lie far off in the imagined future, sticking with a treatment plan is often difficult. Achieving diet, weight and exercise goals and finding the best drug regimen with the most tolerable side effects require education, patience and commitment, without any obvious rewards (beyond seeing a lower number on the blood pressure monitor)  – just like many of the most worthwhile things in life.

What about Meditation?

People skilled in meditation can certainly lower their blood pressure at the time they are practicing the discipline, but blood pressure returns to baseline when they return to routine activity. If the practice of meditation encourages mindfulness in other areas of life it may well decrease anxiety, reduce tension,  and  improve the self-discipline necessary for dietary restraint, regular exercise, and sufficient sleep – indirectly helping with blood pressure control.

 

 

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