Make Your Own Stethoscope

Introduction

Have you ever wondered what happens to the heart as we exercise intensely? How does its beating change? A doctor can figure this out by using a tool called a stethoscope, which is a long, thin plastic tube that has a small disc on one end and earpieces on the other end. In this activity, you will make a homemade stethoscope and use it to measure peoples' heart rates at rest and after exercising.

Materials

• Duct tape or other strong tape
• Scissors
• Plastic funnel
• A cardboard tube from a paper-towel roll
• Stopwatch or clock that counts seconds
• A volunteer who can safely exercise intensely for one minute
  
  

What Happened?

When people exercise, their bodies need more oxygen, and consequently their hearts beat faster and their heart rates increase. This is why you most likely found that when your volunteer exercised, the heart rate increased compared to the resting heart rate. In addition, genetics, gender, age, and health all affect people's heart rates. The heart rates in people who exercise regularly usually will not increase as much during exercise. Regular exercise strengthens the heart so that it does not need to work as hard to do the same amount of exercise.

While you can determine someone's resting heart rate by counting the number of beats in 15 seconds and multiplying by four to get the beats per minute (bpm), to calculate a heart rate immediately after exercise it is better to count the number of beats for 10 seconds and multiply that value by six (to get the bpm). Because the heart will quickly slow down after exercise, the heart rate should be measured immediately after a person has stopped exercising (or while they exercise, if possible).

Digging Deeper

You are probably familiar with how a doctor uses a stethoscope from visits to your own doctor — the doctor puts the stethoscope's flat disc or hollow cup on a patient's body, and the earpieces go into the doctor's ears. But how does the stethoscope work? How does it allow the doctor to hear sounds inside of the patient's body?

The disc and the tube of the stethoscope amplify small sounds, such as the sound of a patient's lungs, heart, and other small sounds within the body, making them sound louder. The amplified sounds travel up the stethoscope's tube to the earpieces that the doctor listens through. Heartbeats can easily be heard using a good stethoscope. Every time a person's heart beats, the heart, which is a powerful pump, contracts and pushes blood through the body. This blood is full of oxygen, so the heart helps deliver oxygen to the rest of the body, while picking up nutrients and delivering them to other parts of the body.

For Further Exploration

• There are several different ways you can make a homemade stethoscope. For example, instead of a cardboard tube you could use a short piece of garden hose or plastic tubing. Or you could try varying the length of the tube. You could even try different sized funnels. What homemade stethoscope design works the best? What goes into making a good stethoscope design?
• In this activity you only tested one person's heart rate, but you could try your stethoscope on several different people. How do different peoples' heart rates compare to each other? Do they all change a lot after exercising, or do some change only a little bit or not at all? Does the heart rate correlate with a factor such as age, gender, or BMI?
• A person should use at least 50% of their maximum heart rate when they are exercising for the activity to qualify as exercise. You can find out more about maximum and target heart rates and then apply this information to create an exercise routine. Based on this information, what physical activities does a given person do that qualifies as exercise?

Related Resources

Project Ideas

Links

• Blog Post: Heart-health Science: Is Your Heart Really Heart-Shaped?

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