Investigating Ventilation

Question 1

What is tidal volume?

Answer 1

The volume of air breathed in or out of the lungs PER breathe.

Question 2

What is breathing rate?

Answer 2

Number of breathes in a minute.

Question 3

What is vital capacity?

Answer 3

The maximum volume of air that can be forcibly exhaled after a maximal intake of air.

Question 4

What is ventilation rate?

Answer 4

The volume of air breathed in or out in a minute. It’s the rate at which someone breathes.

Question 5

How do you calculate ventilation rate?

Answer 5

Tidal Volume x Breathing Rate

Question 6

1) How does the medulla control breathing rate? Describe the stage involving the inspiratory centre.

Answer 6

• Inspiratory centre in the medulla sends nerve impulses to the intercostal and diaphragm muscles to make them contract.
• This increases the volume of the lungs, which lower the pressure in the lungs. Inspiratory centre also sends nerve impulses to expiratory centre to inhibit action of it.
• Air enters lungs due to pressure difference btwn lungs and air outside.
• As lungs inflate, stretch receptors in the lungs are stimulated. The stretch receptors send nerve impulses back to the medulla. These impulses inhibit inspiratory centre.

Question 7

2) How does the medulla control breathing rate? Describe the stage involving the expiratoy centre.

Answer 7

• The expiratory centre (no longer inhibited) sends nerve impulses to the diaphragm and intercostal muscle to relax. This causes the lungs to deflate, expelling air.
• As the lungs deflate, the tretch receptors become inactive. The inspiratory centre is no longer inhibited and the cycle starts again.

Question 8

How can spirometers be used to measure tidal volume and breathing rate?

Answer 8

1. A spirometre has an oxygen-filled chamber with a movable lid. A person breathes though a tube connected to the oxygen chamber.
2. As the person breathes in the lid of the chamber moves down. When they breathe out it moves up.
3. These movements are recorded by a pen attached to the lid of the chamber - this writes on a rotating drum, creating a spirometer trace.
4. The soda in the tube the person breathes into absorbs CO2. Must use medical grade oxygen.

Question 9

Why does the total volume of gas in a spirometer chamber decrease over time?

Answer 9

Air that is breathed out is a mixture of oxygen and carbon dioxide. The carbon dioxide is absorbed by the soda lime – so there’s only oxygen in the chamber which the peron inhales from. As this oxygen gets used up by respiration, the total volume decreases.