Measuring Gas Exchange
Applied Science: BTEC Level 3 National Extended Diploma, topic 4.6.3
Measuring Lung Function
The function of the lungs can be measured using a spirometer. Measuring gas exchange allows doctors to identify problems in the lungs.
Spirometer
- A spirometer is a piece of apparatus that measures the gas exchange in the lungs.
- A spirometer measures the volume of air that is inspired and expired by an individual.
- An individual breathes into and out of a spirometer to measure the lung function.
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Tidal volume & vital capacity
- A spirometer can measure the tidal volume.
- Tidal volume is the volume of air in a normal breath (at rest).
- The average tidal volume is about 0.4 dm3 − 0.5 dm3.
- A spirometer can measure vital capacity.
- Vital capacity is the maximum volume of air that can be breathed in and out of the lungs.
Ventilation rate
- A spirometer can measure the ventilation rate.
- The ventilation rate is the number of breaths a person takes per minute (at rest).
- The average ventilation rate is about 15 breaths per minute.
Forced expiratory volume
- A spirometer can measure forced expiratory volume.
- Forced expiratory volume is the maximum volume an individual can expire in one second.
- The forced expiratory volume cannot be more than the total volume of gas in the lungs.
- This is because there is always a small amount of air that cannot be expired (the residual air). The residual air ensures the alveoli do not close.
Pulmonary ventilation rate (PVR)
- Pulmonary ventilation rate can be calculated using the equation:
- PVR = tidal volume × breathing rate
- If you are given two of these values, the equation can be rearranged to calculate the third value.
Exercise
- During exercise, the following can be seen on the spirometer trace:
- Increased tidal volume.
- Increased ventilation rate.
- Constant vital capacity.
- The tidal volume and ventilation rate increase during exercise as more oxygen is required for respiration.
- Respiration provides the energy required for exercise (e.g. for increased muscle contraction).
Test yourself on Measuring Gas Exchange
Which of the following statements about measuring lung function are true?
What is the term given to the maximum volume an individual can expire in one second?