Breathing rate, lung volumes and healthy lungs

1Why do you pant after a race?

After a 100 m sprint on the school field, you breathe faster and deeper, and it takes a few minutes before your breathing settles. Your working leg muscles were respiring much faster than usual (Unit 5), using more oxygen and making more carbon dioxide. Breathing faster and deeper brings in more ${\mathrm{O}}_2\backslash mathrm\{O\_2\}$ and removes the extra $\mathrm{C}{\mathrm{O}}_2\backslash mathrm\{CO\_2\}$.

Doctors and scientists measure breathing in two ways: how often you breathe (the breathing rate), and how much air each breath moves (lung volumes). This lesson shows how to measure both, and ends with how to keep your lungs healthy.

2Experiment: breathing rate at rest and after exercise

1. Sit quietly for 3 minutes. Your partner counts your breaths for 30 seconds, counting each rise of your chest as one breath, while you breathe normally.
2. Do 2 minutes of step-ups on a low, firm step (or skipping on the spot).
3. Sit down at once. Your partner counts your breaths for the first 30 seconds.
4. Keep counting for 30 seconds every minute until your breathing is back to its resting rate. The time this takes is your recovery time.

Safety. Exercise only as hard as is comfortable for you. Stop if you feel dizzy or have pain in your chest. A student with asthma keeps their inhaler nearby, and may record results instead of exercising.

Table 1: Sample class results (sample data, for illustration)

Conclusion: in every student, the breathing rate more than doubled after exercise, then fell back to the resting rate within a few minutes. Fitter people usually recover faster.

3Reading a spirometer trace

A spirometer records each breath as a rise (breathing in) and a fall (breathing out). Figure 1 shows a simplified trace: a person breathes normally, then takes the deepest breath in they can, breathes out as far as they can, and goes back to normal breathing.

Figure 1: A spirometer-style trace. The data are illustrative, not a real person's measurements.

4Keeping the gas exchange system healthy

Smoking and the cilia. Tar and other chemicals in cigarette smoke paralyse or destroy the cilia that line the bronchi and bronchioles. Smoke also makes the airways produce more mucus, which the damaged cilia cannot move. Mucus, dust and bacteria collect in the airways, causing a lasting cough and more chest infections. (Unit 12 looks at tobacco as a drug.)

Asthma. In asthma the airways are easily inflamed. When something triggers an attack, such as dust, smoke, pollen, cold air or exercise, the smooth muscle in the walls of the bronchioles contracts, the lining swells and extra mucus is made (Figure 2). The airways narrow, and the person wheezes, coughs and struggles to breathe out. A reliever inhaler delivers a medicine that relaxes the muscle and widens the airways.

Figure 2: A bronchiole cut across, normally and during an asthma attack.

Smoke from cooking fires. In Rwanda's 2022 census, 76.1% of households cooked mainly with firewood, 17.3% with charcoal and only 4.6% with gas. In the City of Kigali, charcoal was the most common fuel, used by 57.6% of households. The World Health Organization reports that smoke from such fuels contains small particles that reach deep into the lungs, and that in a poorly ventilated home the fine particles can reach 100 times the acceptable level. Women and children, who spend the most time near the fire, breathe the most smoke. Burning charcoal also gives off carbon monoxide, a poisonous gas that you cannot see or smell.

What a household can do:

• cook outdoors, or in a kitchen with a window, a door open to the outside, or a chimney;
• use an improved cookstove, which burns less fuel and makes less smoke, or gas or biogas where possible;
• burn dry wood, which makes less smoke than damp wood;
• keep babies and young children away from the fire;
• never bring a burning charcoal stove into a closed room where people sleep.