Problem

What factors can affect lung capacity?

Introduction

When you inhale, air rushes into your lungs. The amount of air that rushes in during a normal breath is called the tidal volume. Your lungs have the capacity to accept a much larger volume of air than you normally inhale. For example, you might be asked to take a deep breath during a medical exam. Scientists use the term vital capacityto describe the largest volume of air that you can exhale after you take a deep breath.

In this lab, you will measure tidal volume and vital capacity. Then you will design an experiment to investigate a factor that can affect vital capacity.

Skills Focus

Measure, Form a Hypothesis, Design an Experiment, Interpret Graphs

Materials

• round balloons

• metric ruler

• meterstick

Safety

Do not test your vital capacity if you are ill or if you have difficulty breathing. If at any point you feel faint or dizzy, stop what you are doing and sit down. Ask your partner to inform your teacher of the problem. If you have an allergy to latex, do not handle the balloons. Make sure you and your partner use different balloons.

Pre-Lab Questions

  1. Control Variables What is the one difference between the procedures in Part A and Part B?

______

2. Design an Experiment Why must you use round balloons for this experiment?

______

______

3. Predict Which do you think will be greater—your estimated vital capacity or your measured vital capacity?

Why?

______

______

______

Procedure

Part A: Measuring Tidal Volume

1. Stretch a round balloon lengthwise several times.

  1. Inhale normally, and then exhale normally into the balloon. Immediately pinch the balloon shut so that no air escapes.
  2. Keep pinching the balloon as you place it on a flat surface. Have your partner measure the diameter of the balloon at its widest point as shown in Figure 1. Record the measurement in Data Table 1.
  3. Allow the balloon to deflate. Repeat Steps 2 and 3 two more times.
  4. Calculate the mean for the measurements from the three trials and record your answer in the data table.
  5. Look at the next page figure 2to fill out the lung volume to complete Data Table 1.

Figure 1 How to measure the diameter of the balloon

Data Table 1: Tidal Volume
Trial / Tidal Volume
(balloon diameter cm) / Lung Volume (use fig 2)
1
2
3
Mean

Part B: Measuring Vital Capacity

  1. Take as deep a breath as possible. Then, exhale as much air as you can from your lungs into the balloon. Immediately pinch the balloon shut so that no air escapes.
  1. Keep pinching the balloon as you place it on a flat surface. Have your partner measure the diameter of the balloon at its widest point. Record the measurement in Data Table 1.
  1. Allow the balloon to deflate. Repeat Steps 6 and 7 two more times.
  1. Calculate the mean for the measurements from the three trials and record your answer in the data table.
  1. On the graph in Figure 2, balloon diameter in centimeters is plotted against volume in cubic centimeters (cm3). Use the graph to find the volumes that correspond to your diameter measurements. Record your results in Data Table 2.

Data Table 2: Vital volume
Trial / Vital Volume
(balloon diameter cm) / Lung Volume (use fig 2)
1
2
3
Mean

Figure 2 Lung volume versus balloon diameter

Part C: Estimating Vital Capacity

Research has shown that vital capacity is proportional to the surface area of a person’s body. You can estimate your surface area if you know your height and your mass.

  1. You can use the meterstick to measure your height in centimeters. Or you can convert your height in inches to centimeters by multiplying the number of inches by 2.54.

Height: ______

  1. To convert your mass in pounds to kilograms, multiply the number of pounds by 0.454.

Mass:______

  1. Use Figure 3 to estimate the surface area of your body. Find your height on the scale on the left. Find your mass on the scale on the right. Use a ruler to draw a straight line between those points. The location where the line crosses the middle scale is your estimated surface area.

Surface area: ______

Figure 3 Estimated surface area based on height and mass

14. To calculate the estimated vital capacity of your lungs, multiply your surface area in square meters by the ratio of vital capacity to surface area. Based on research, the ratio is 2000 cubic centimeters per square meter for females. For males, the ratio is 2500 cubic centimeters per square meter. Calculate and record your answer.

Estimated vital capacity = surface area (m2) × ratio

Estimated vital capacity:

Analyze and Conclude

  1. Analyze Data How did your estimated vital capacity compare with your measured vital capacity? Was your prediction in Pre-Lab Question 3 correct?

______

  1. Draw Conclusions What could have caused any difference between the estimated value and the measured value?

______

  1. Design an Experiment Why is it important to do more than one trial when making measurements?

______

  1. InferIn Step 14, why did females and males use different ratios to calculate estimated vital capacity?

______

  1. Analyze Data How did your position affect the vital capacity of your lungs? Suggest an explanation for any difference you found.

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  1. Perform Error Analysis In Part A, why might the volume in the first trial be smaller than in the second and third trials? How could the procedure be adjusted to avoid this result?

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  1. Predict How would smoking affect lung capacity, and why?

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