Lung Capacity Lab
Learning Objectives
Students will be able to:
- Measure their own lung capacity using simple tools
- Compare lung capacity measurements to predicted values
- Analyze class data to identify patterns
- Connect lung capacity to respiratory health
Background: Lung Volumes
Tidal Volume (TV)
Air in a normal breath
~500 mL
Vital Capacity (VC)
Maximum air you can exhale after maximum inhale
~4-5 L for adults
Residual Volume
Air that always stays in lungs
~1.2 L
Total Lung Capacity
Maximum air lungs can hold
~6 L for adults
Materials (Per Group)
Option A: Balloon Method
- Round balloons (all same type)
- Flexible measuring tape or string + ruler
- Conversion chart (below)
- Data recording sheet
Option B: Water Displacement
- Large container (5+ liters)
- Plastic tubing
- Graduated cylinder or measuring cup
- Basin to catch water
Procedure: Balloon Method
Measuring Vital Capacity
- Stretch the balloon several times to make it easier to inflate
- Take the deepest breath you can
- Exhale ALL the air you can into the balloon in ONE breath
- Pinch the balloon closed (don't tie it)
- Measure the circumference at the widest point
- Record the circumference in centimeters
- Repeat 2 more times; use the average
Measuring Tidal Volume
- Use a new balloon (or fully deflate)
- Take a normal breath
- Exhale normally into the balloon
- Measure circumference
- Repeat 2 more times; use the average
Balloon Circumference to Volume Conversion
| Circumference (cm) | Volume (mL) | Circumference (cm) | Volume (mL) |
|---|---|---|---|
| 20 | 135 | 50 | 2,100 |
| 25 | 265 | 55 | 2,800 |
| 30 | 455 | 60 | 3,600 |
| 35 | 720 | 65 | 4,600 |
| 40 | 1,075 | 70 | 5,750 |
| 45 | 1,530 | 75 | 7,075 |
Formula: Volume = (4/3) × π × (circumference / 2π)³
Predicted Vital Capacity
Compare your measured vital capacity to predicted values based on height:
| Height (cm) | Predicted VC - Female (mL) | Predicted VC - Male (mL) |
|---|---|---|
| 140 | 2,100 | 2,400 |
| 150 | 2,500 | 2,900 |
| 160 | 3,000 | 3,400 |
| 170 | 3,500 | 4,000 |
| 180 | 4,000 | 4,600 |
Note: These are averages. Individual variation is normal! Athletic individuals often have higher values.
Data Recording Sheet
| Measurement | Trial 1 | Trial 2 | Trial 3 | Average |
|---|---|---|---|---|
| Vital Capacity - Circumference (cm) | ||||
| Vital Capacity - Volume (mL) | ||||
| Tidal Volume - Circumference (cm) | ||||
| Tidal Volume - Volume (mL) |
My height: _______ cm
My predicted vital capacity: _______ mL
My measured vital capacity: _______ mL (______% of predicted)
Class Data Analysis
Compile class data and calculate:
- Class average vital capacity
- Range (lowest to highest)
- Average tidal volume
Analysis Questions:
- What was the range of vital capacity in your class? Why is there variation?
- How does height correlate with lung capacity? Did taller students generally have larger capacities?
- How many breaths per minute would you need to breathe 6,000 mL of air using only tidal volume?
- If someone's vital capacity decreased by 20% due to lung disease, what activities might become difficult?
- How might long-term exposure to air pollution affect these measurements over time?
Unit 3 Summary
Respiratory Anatomy
Air flows through increasingly smaller airways to 300 million alveoli with huge surface area.
Gas Exchange
O2 and CO2 diffuse across ultra-thin membranes between alveoli and blood.
Defense Systems
Nose hairs, mucus, cilia, and macrophages protect against particles—but struggle with PM2.5.
Health Effects
Particles cause inflammation, worsen asthma, and can lead to long-term lung damage.
Key Takeaway
Lung capacity varies based on body size, fitness level, and health status. Measuring lung capacity gives us a window into respiratory health. Long-term exposure to air pollution can reduce lung capacity and function over time—which is why protecting indoor air quality matters for long-term respiratory health.