Your blood pressure numbers

By EDMUND MEINHARDT

VIEW ON HEALTH

The circulatory system provides nourishment to all of the body's tissues. It is how the oxygen and nutrients derived from the air you breathe and the food you eat reach the cells in your body. Oxygen-rich blood is forced by powerful contractions of the heart muscles through the arteries and deoxygenated blood returns to the heart through the veins.

The heart must contract powerfully because the journey of the blood through the arteries, capillaries and veins is a long one. Laid out in one continuous line, a child's blood vessels would stretch 60,000 miles, according to the Franklin Institute. An adult's would be more than 100,000 miles long.

Blood pressure is the force of the blood pushing against arterial walls. It is highest when the heart beats, and lowest when the heart is resting between beats. Both of these states are important indicators of how well the circulatory system is functioning, and blood pressure measurements are expressed using a number to represent each one.

The higher number, representing the pressure while the heart is at work, is called systolic pressure. The lower number, representing the pressure while the heart is resting between beats, is called diastolic pressure. Pressure is measured in millimeters of mercury, abbreviated mmHg. Normal systolic pressure is somewhere between 90 and 130 mmHg and normal diastolic pressure ranges from 50 to 80 mmHg. A measurement of 120 systolic and 80 diastolic would be written 120/80 and read as "120 over 80."

Your heart works very hard without resting for more than a second at a time over the course of your lifetime. According to fact sheets on eHealthMD.com, the average heart beats 60 times per minute, 3,600 times an hour, 86,400 times per day, 31.5 million times per year, and more than 2.4 billion times in an average lifetime. During the course of that lifetime, the heart will pump about 42 million gallons of blood - which is enough to fill 3.3 supertankers. In the course of doing so, that single human heart will expend enough energy to lift a battleship out of water.

The heart, therefore, exerts tremendous stress on the arteries. Fortunately, they are designed to withstand it. They are very smooth on the inside, which allows blood to flow rapidly, and very strong and elastic on the outside. The condition of the arteries has a direct influence on blood pressure. Larger arteries have lower blood pressure. Fatty deposits can collect on arterial walls, reducing the smoothness and increasing blood pressure. Also, as we age, collagen fibers decrease, which can reduce the overall elasticity of arterial walls and result in an increase in blood pressure.

Dr. Theodore L. Goodfriend, professor of medicine and pharmacology at the University of Wisconsin Madison, said the systolic pressure is now considered to be the more important of the two numbers.

"This is a change since I went to medical school," Goodfriend said. "The heart contracts one-third of the time and is at rest two-thirds of the time. If you take an average of the blood pressure over time, you would come out with a number that is closer to the diastolic pressure. But the systolic tells us more about what to expect from the blood pressure in terms of damage to the arteries and damage to the heart. The contraction of the heart affects the arteries like a hammer stroke."

Many factors can influence blood pressure, including diet, exercise, drugs and disease. It is important to monitor blood pressure because changes in blood pressure can indicate an increased risk for some medical conditions or events such as stroke. Blood pressure, respiratory rate, pulse and temperature are the four "vital signs," measurements taken to quickly assess a patient's condition.

The average person, who is not known to have high blood pressure, should have it checked once or twice a year, Goodfriend said.

According to WebMD, chronic high blood pressure, a condition known as hypertension, is one of the risk factor for strokes, heart attacks, heart failure and arterial aneurysms. It is a leading cause of kidney failure. A reading of 140/90 is considered high blood pressure. Most people with this condition have no symptoms, which is a good reason to get regular checkups.

Goodfriend said readings lower than 140/90 can still be worrisome if other factors are present, such as obesity, diabetes, high cholesterol or being an African-American male.

"Whatever your blood pressure is, you should try to keep it low," Goodfriend said.

Hypertension can be managed. Your physician will work with you to come up with a plan for controlling, and if possible, reducing your blood pressure readings. Reducing salt intake, exercising and giving up smoking can all contribute to lowering your blood pressure. Patients who are obese can reduce their blood pressure by losing weight. Other dietary measures include reducing saturated fat and limiting alcohol consumption.

Patients with hypertension should usually avoid vasoconstrictors, which are substances that reduce the size of blood vessels. Vasoconstrictors include caffeine, antihistamines and decongestants.

Dr. Ed Roccella, coordinator of the National High Blood Pressure Education Program at the National Heart, Lung and Blood Institute, said the blood pressure of the average American is decreasing, and that there has been a 60 percent reduction in stroke mortality rates since the 1960s. Roccella said lifestyle changes can be very effective in controlling high blood pressure.

"Most Americans consume too much salt," he said. "And most of us could afford to shed a few pounds. Ten pounds, even five pounds can make a big difference, even for someone who is obese. Exercise, just thirty minutes of walking a day, improves blood pressure."

Roccella also recommended a diet rich in vegetables and low-fat dairy.

"For some, that can mean they won't need drugs to control blood pressure," Roccella said. "For others, it will make the drugs work better."

Hypotension is abnormally low blood pressure. According to WebMD, chronic low blood pressure is almost never serious. Sudden drops in blood pressure, however, can cause inadequate blood flow to the heart, lungs and brain. Dizziness and lightheadedness can result. It most commonly occurs when standing up from a sitting or lying position, and under these circumstances is referred to as postural or orthostatic hypotension.

A sudden plunge in blood pressure can be serious, and can be indicative of life-threatening conditions such as severe allergic reaction (anaphylaxis), severe blood infection (sepsis), heart failure or severe dehydration.

Still, to be healthy, you should keep your blood pressure as low as possible, Goodfriend said.

"The higher the blood pressure, the shorter the lifespan," Goodfriend said. "A person should strive for the lowest blood pressure they can tolerate."