September 2005

Blood pressure is measured in millimeters of mercury with an instrument known as a sphygmomanometer (pronounced: sfig-mo-mah-nah-muh-ter) and a stethoscope.


Our hearts pump blood throughout our bodies non-stop, 24/7, transporting oxygen and nutrients to our organs to keep us alive and functioning. As blood circulates throughout the body, it is possible to measure blood pressure--the force with which blood impacts artery walls. In some people, blood pressure is at unhealthy, high levels. Fortunately for them, there are life-style changes and medications that can be used to control blood pressure. At least one of these medications, chlorthalidone, is manufactured using chlorine chemistry.

An Inside Look at High Blood Pressure

According to the American Heart Association, nearly one in every three U.S. adults has high blood pressure. This condition develops when blood vessels (arteries and veins) are too narrow for the flow of blood. High blood pressure causes a strain on the heart which is forced to work harder to pump blood through blood vessels that are too narrow. It also causes damage to blood vessels and can even affect important organs that must be supplied with blood, such as the kidneys and the brain.

Because there are no outward signs to indicate high blood pressure, people can have this condition for years without knowing it. In fact, the American Heart Association estimates that 30 percent of people with high blood pressure don't know they have it. That is why it is important to have your blood pressure checked regularly. If your doctor diagnoses high blood pressure, it can be controlled with life-style changes, such as diet, exercise and medication, such as chlorthalidone.

Expressing Blood Pressure in Numbers

Two numbers are used to describe blood pressure:

  1. Systolic: The higher number that represents the pressure against artery walls when the heart beats or "contracts" and pumps blood.
  2. Diastolic: The lower number that represents the pressure against artery walls when the heart relaxes in between heart beats.

According to the American Heart Association, blood pressure less than 120 (systolic) over 80 (diastolic) is generally considered ideal for teens and adults. Blood pressure frequently is written as a fraction, for example, 120/80 millimeters of mercury. It might be reported orally as "120 over 80."

Chlorthalidone to the Rescue

To reduce high blood pressure in patients, doctors often prescribe a diuretic. Diuretics are medicines that work on the kidneys to remove salt and water from the body by promoting the formation of urine. Chlorthalidone is a popular diuretic. Doctors know that some people with high blood pressure are sensitive to the amount of salt in their diets: the more sodium they take in, the higher their blood pressure. (Remember the formula for common table salt is NaCl, sodium chloride.) Chlorthalidone helps reduce salt levels by causing salt to be excreted in the urine.

Removing water from the body also reduces a person's blood pressure because it decreases the volume of blood circulating through the arteries and veins (Water is a major component of blood.) Reducing the volume of blood that is channeled through narrow blood vessels reduces the overall pressure on the vessel walls. Because they remove water from the body through the urine, diuretics such as chlorthalidone are commonly called "water pills."

Chlorthalidone Close-up

Chlorthalidone, C14H11ClN2O4S, is a double-ring organic molecule. The hexagonally-shaped parts of the molecule, the rings, are made up mostly of carbon and hydrogen. Each molecule of chlorthalidone contains one chlorine atom attached to one of the rings.

The molecular structure of

Blood Pressure:   It's Variable

Blood pressure changes as we grow. Babies have lower blood pressure than teens and adults; they start out life with a systolic pressure of about 90. As they grow, their blood pressure increases. 

A person's blood pressure also changes somewhat from minute to minute and is affected by activity level, body temperature, diet, emotional state, posture and medications. For that reason, doctors may ask for more than one measurement of a patients' blood pressure. Sometimes patients are encouraged to monitor and keep records of their own blood pressure. Many pharmacies and supermarkets have blood pressure measurement devices that are convenient and easy to use.

Follow-up Activities

  1. If you have access to a free blood pressure station, monitor your blood pressure for one week and keep a log of it, noting the date and time of the reading. Graph your systolic and diastolic results. (Graph paper is available below.) How variable is your blood pressure over the course of one week?

  2. A "risk factor" is defined as something that increases a person's chances of developing a disease or medical condition. Research and list the risk factors for high blood pressure. What can a person do to lower his/her risk of developing high blood pressure?  

Heart Healthy Activities and
Resources for Kids:

American Heart Association

BAM: Body and Mind (US Centers
for Disease Control and Prevention)

KidsHealth: All About the Heart

Graph Paper

For a list of previous "Chlorine Compound of the Month" features, click here.


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