High and Low Blood Pressure

High or Low Blood Pressure?

Purpose:

The purpose of this experiment is to compare blood pressure as related to gender and athletic status.

Hypothesis:

I predict that males have a higher blood pressure than women and athletes have a higher blood pressure than non athletes

Background Info:

Blood pressure is the amount of force that blood pushes against the inside walls of blood vessels as it passes through. This pressure is initially produced by the contracting heart and is necessary to push blood along to all organs in the body. Doctors can take a blood pressure by using a sphygmomanometer (blood pressure cuff). The idea behind this instrument is that the cuff is tightened around the arm so much that the brachial artery is shut off. Then, by slowly loosening the cuff, blood is allowed to resume passage through that artery. The first amount of blood to break through the cuffed area will be the blood surge produced when the left ventricle contracts, called systole. The systolic pressure will continue to push blood past the cuff area until the pressure is at its lowest amount in the artery. This lower pressure reflects the blood pushing against the artery wall between heart contractions, or during diastole. By using a stethoscope, you can listen to sounds that tell you when the systolic pressure is pushing through and when the diastolic pressure is reached. The ratio of the systolic to diastolic pressure in mm/Hg or torr is the blood pressure. A common blood pressure for teenagers is 110/70. A common BP for young adults is 120/80. Both systolic and diastolic pressures rise as one gets older.

As blood leaves the heart and enters the aorta is under high pressure of about 120 torr given to it by the force of left ventricle contracting. This surge of blood from the heart presses against the inside walls of the arteries and is called systole. When the left ventricle relaxes, no new blood enters the arteries. However, the blood already in the arteries are still exerting a force against the inside of the artery wall of abut 80 torr. This person's blood pressure (BP) during relaxation of the ventricle is called diastole. A person's blood pressure reading is the ratio of the systolic BP to the diastolic BP. So the average blood pressure of an adult person at rest is about 120/80 mm/Hg.

Throughout the arteries, the average systolic blood pressure is about 100 torr. This is sufficient pressure to drive the blood into the system of capillaries where the BP drops to about 27 torr, then toward the veins where the BP drops to about 2 torr. The BP in the venous system is so low that the pull of gravity, especially on the legs while standing, is so great that veins have one-way valves to assure that blood always flows toward the heart. Aiding the valves to maintain one-way flow are the leg muscles which squeeze the veins as the muscles contract. This skeletal muscle pump is a good reason for all persons to walk regularly. Even so, blood barely makes it back to the right atrium.

The fall in BP from 100 torr in the arterial system to 2 torr in the venous system is mainly explained by resistance to blood flow. The blood, after leaving the heart, passes into vessels of smaller and smaller diameter. This slows the flow. Also, there is the friction on the blood by the blood vessel walls. Both of these forces, are called peripheral resistance. Peripheral resistance can be increased if arteriole diameters are reduced as by the formation of fatty deposits on the walls of the blood vessel. Blood trying to squeeze through such a small diameter pushes harder against the walls of the blood vessel, increasing the BP. This can lead to high blood pressure, called hypertension. Risk factors for this condition are heredity, a diet high in fats, smoking, and lack of exercise.

Materials:

Sphygmomanometer/blood pressure cuff

Alcohol swabs

Method:

1) Wrap the blood pressure cuff snugly around your partner's bare upper arm. Have your partner lay his or her arm down on a table in a relaxed way as horizontal as possible.

2) Use an alcohol swab on the ear pieces of the stethoscope and put the ear pieces in your ears.

3) Place the plastic diaphragm end of the stethoscope on your partner's brachial artery (inside junction of the elbow). Hold it there firmly.

4) Close the metal valve on the cuff by turning it clockwise.

5) Pump the rubber hand bulb until the mercury (or needle) on the gauge reaches 140 mm/Hg. This should stop all blood passing through the artery.

6) Slowly open the metal valve by turning counterclockwise, so that the mercury (or needle) drops slowly on the gauge.

7) As the pressure of the cuff on the arm is released, blood will begin to push through the artery. The first sound you hear will be the systolic pressure. Make a mental note of the number on the gauge, and continue allowing the mercury to drop slowly.

8) You will hear heart sounds for a short time, then all sounds will disappear. This means that the artery diameter has returned to normal and blood is passing through under diastolic pressure. Make a mental note of the number on the gauge.

9) Open the valve completely to let all air out of the arm cuff. The systolic pressure over the diastolic pressure is your partner's blood pressure.

Results: