Taking a pulse

MadSci Network: Edible/Inedible Experiments Archive

Taking a pulse

Area of Science: Biological Sciences
Meant for Grade 4-6 (age 8-10).
This experiment is inedible.
An adult need not be present.

Overview:
Take your pulse at mutliple sites. Relate the pulse to heartbeat.

Equipment:
Nothing - free fingers.. a diagram of the body and a stethoscope may be helpful.

Safety:
When taking the carotid pulse in the neck, be certain to take one side at a time!

How to do the experiment:
Try taking your pulse at the following sites (see picture)

Radial Pulse: This is probably what we're most familiar with when visiting the doctor's office. Take two fingers, preferably the 2nd and 3rd finger, and place them in the groove in the wrist that lies beneath the thumb. Move your fingers back and forth gently until you can feel a slight pusation - this is the pulse of the radial artery which delivers blood to the hand. Don't press too hard, or else you'll just feel the blood flowing through your fingers! You can even use your thumb.

Carotid Pulse: The carotid arteries supply blood to the head and neck. You can feel the pulse of the common carotid artery by taking the same two finger and running them alongside the outer edge of your trachea (windpipe). This pulse may be easier to find that of the radial artery. Since the carotid arteries supply a lot of the blood to the brain, it's important not to press on both of them at the same time!

femoral pulse: The femoral atery carries blood to parts of the leg. Aside from the carotid artery, it is another common site to check for a pulse in an emergency situation. Think of an imaginary line running from your hip to the groin. The approximate superficial location of the femoral artery lies 2/3 of the way in from the hip. Admin note: the other following sites can also be tried:

facial artery: Gently run a finger along the lower edge of the jaw bone. Just beyond the 'chin' on either side, you might be able to feel the pulse of the facial artery.
brachial artery: Flex your bicpes muscle. Press your thumb or a few fingers into the groove created between the biceps and other muscles, approximately 5cm from the armpit. You should be able to feel the pulse of the brachial artery. This is the major artery supplying blood to the arms.
Abdominal aorta: Very thin individuals may be able to note a slight pulsation beneath the stomach when lying down in a relaxed position. This pulsation is caused by the abdominal aorta, the continuation of the aorta from the heart. At the level of the umbilicus (belly button), the aorta splits into the left and right common iliac ateries which deliver blood to the legs.
Popliteal atery: This artery lies behind the knee. Bend your knee slightly and feel in the soft area behind the knee.

Explanation:
The pulse represents the beating of the heart, specifically the ejection of blood from the left ventricle to the general circulation of the body. The ventricles (right and left) have two phases: diastole or the time when the ventricles 'rest' so they can fill with blood, and systole, the time when the ventricles contract to send blood either to the lungs (from the right side of the heart), or to the rest of the body (from the left side of the heart). Blood from the left side of the heart first enters the aorta, the largest artery in the body. The aorta branches into smaller arteries which carry blood to all part of the body.

The pulse represents the variation in blood pressure from diastole to systole. During diastole blood pressure falls, but increases after systole as the heart pumps more blood into the arteries. You feel this difference when taking your pulse. Doctors use a device called a sphygmomanometer (blood pressure cuff) to measure the systolic and diastolic blood pressures. The average adult has a systolic blood pressure ~120-150 mm mercury, an average diastolic blood pressure ~80 mm mercury, and an average pulse of 72 beats/minute.

If you have a stethoscope try listening to your heart while taking your pulse. Your heart produces two sounds, often called 'lub' and 'dub.' The second,'dub' sound coincides with the ejection of blood from the ventricles In actuality, the sound is produced by the aortic and pulmonic valves closing behind the ejected blood. The aortic valve opens from the left ventricle into the aorta; the pulmonic valve from the right ventricle into the pulmonary artery.

When does the pulse occur with respect to the second heart sound? the first heart sound?

Useful References:
The human heart, an exploration

Further comments:

Experiment submitted on Sun Mar 2 21:58:57 1997 by:
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