Today a large number of scientists are working very hard to learn more about the body systems that affect gas transport and the diseases that affect it. Let's take a closer look at how they discovered the things we know about the respiratory system.

## How do we measure breathing?

A spirometer is a piece of equipment that scientists use to measure lung capacity and the amount of air a person normally breathes in and out.  You will have an opportunity to make your own spirometer in activity #1.

### A modern electronic spirometer

 Basic idea of measuring air exchange, using a "spirometer." As air is taken in (from the "oxygen chamber" in the apparatus on the left), the floating drum drops down. At the same time the writing arm on the recording drum moves up, indicating inhalation. Opposite effects occur during exhalation.

How can you make a good estimate of the amount of air you breathe in a day?

• One way to do this is to multiply the amount of air you breathe in one breath x the number of breaths you take in a minute x 1440, which is the number of minutes in a day.
• Can you think of any other ways?

Every day our body breathes in and out as much as 10,000 liters of air.  If we were talking about soda, this would be enough soda to fill 5000 two-liter bottles. 5000 bottles of soda weigh about the same as 11 average size cars. Knowing that a bottle of soda ways about 4.4 pounds and an average size car ways 2000 pounds, can you figure out how to make this calculation? (Click here for the answer)

You can make a good estimate of how much air you breathe in and out everyday.  To do this observe your breathing rate by counting the number of breaths you take in a minute and  use a spirometer to figure out how much air you breathe in during a single breath at rest (about 0.300 liters is average for a  12 to 13 year old).

A spirometer can tell a doctor how far a respiratory disease has progressed and help determine what the treatment should be (See Hazards).  One of the more common breathing problems in children is asthma, an allergy disease that causes chronic inflammation and swelling of the bronchial tubes.  This limits the amount of air that a person can breathe in and out at a given time.

## How do we know how lungs work?

Sometimes the best way to find out how something works is to take it apart and figure out what the smaller parts do. That's exactly what scientists have done to learn about the lungs.  Some people donate their bodies to medical schools after they die, so that doctors can study the parts and try to figure out how they work.  Animal studies have also been used to learn about the lungs. Scientists look closely at all of the different parts of the lung including the alveoli, bronchiole, bronchial tubes, membrane linings, and the different lobes of the lung.

In living people, physicians can view the inside of the lung using a fiber optic camera, called an endoscope.  Using an endoscope, physicians can observe the lung while it is moving and observe very closely the changes that take place during respiration.

Scientists have also learned about the gas exchange that takes place in the lungs by sampling the air directly. They have learned what makes up inspired air and how it differs from air deep within the lungs. For example, they have learned that when air enters the lung it is greatly humidified in order to facilitate gas exchange. In order to do this, the lung makes the air a bit "thicker" and causes it to stay in the lungs longer, increasing contact time and gas exchange. This is the reason that it is sometimes easier to breathe in a room with a humidifier.

### Inside of a trachea as seen in an endoscopy procedure

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