Blood Pressure

High blood pressure is often called the “silent killer” because it is often symptomless until something catastrophic happens like a stroke. Despite its quiet nature, the condition is commonly treated, especially in the elderly, with the hope of keeping it at 120/80. Although that number is the textbook “normal” blood pressure for healthy adults, normal blood pressure can vary widely from minute to minute in perfectly healthy individuals. It can be pushed higher or lower by different measuring techniques or by maneuvers done by the patient. It can be influenced by exercise, excitement and what the person recently drank. Blood pressure is one of those measurements that can be swayed by the expectations of the person doing the measuring as well as by the patient.

Let’s take a look at these numbers for a minute. The low number (the diastolic) is the pressure of the blood in the artery. If you expanded your blood volume with, say, a transfusion and nothing else changed, that number would rise. The high number (the systolic) is the pressure your heart puts on the blood when it pumps. It is a reflection of the power of the heart muscle to contract and push blood.

Now, a strong heart is a good thing, isn’t it? Shouldn’t a powerful push, say 160/80, be better than 120/80? The answer is yes, when in the context of exertion. But when resting, the heart shouldn’t have to push hard. If it does, that is often because the vessels have become stiffened with plaque – arteriosclerosis. This is one reason high blood pressure sets off alarm bells in the doctor’s office.

Let’s consider again the trained athlete. His heart can pump slower to deliver the same amount of blood because his stroke volume is larger. The slower heart rate at rest means more time to relax between beats for the heart, too. It’s more efficient. But that heart has to squeeze harder to push the bigger load of blood in that higher stroke volume. This means the systolic pressure will be higher than “normal” when the pulse is slow. It’s not unusual or pathological for the trained athlete to have a higher than normal systolic blood pressure combined with a slow heart rate.

For this reason, the healthy individual need not necessarily be concerned about a slow heart rate with an elevated systolic blood pressure. These are normal adjustments as a person becomes more and more fit.

So what about an abnormal diastolic pressure? What does that mean? Remember how I said that the diastolic is the pressure of the blood in the artery and would rise if you added more fluid to it? That’s only partially true because the circulatory system controls the pressure in the blood vessels by adjusting the flow into the capillary beds in the periphery. By tightening the small vessels in the periphery, the body can raise the diastolic blood pressure. Conversely, if the arterioles go wide open, the blood will pool in the periphery and venous return to the heart will slow, even stop. We call this “shock” and we treat it by elevating the limbs of the supine patient so the blood can return to the lungs and heart and be oxygenated and pumped out again.

Dip yourself in cold water and the peripheral vessels will squeeze tight and diastolic blood pressure will rise as blood is forced to the core. Warm yourself in a sauna and the diastolic pressure will fall as your blood flows out to the skin. Alternate between hot and cold and you will generate an invigorating and therapeutic ebb and flow of the blood to the tissues, enhancing delivery of oxygen and nutrition while removing wastes.

So we find that wide ranges of blood pressure – both systolic and diastolic – are normal and necessary for the proper function of the circulatory system. The ability of the system to adjust between exertion and rest, and between warm and cold, is what makes the heart and vessels fit, not the ability to maintain a single value like 120/80.