3.2.7

# Measuring Gas Exchange

Test yourself

## 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.

### Tidal volume

• 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.

### 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.

### Vital capacity

• A spirometer can measure vital capacity.
• Vital capacity is the maximum volume of air that can be breathed in and out of the lungs.

### 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.