Blood and the respiratory system
Blood and the respiratory system

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Blood and the respiratory system

3.1 Spirometry

Lung function can be measured using spirometry. A typical test involves blowing out into a spirometer as hard as possible until the lungs are empty (Figure 10). The forced vital capacity (FVC) is calculated as the total volume of air that can be forcefully blown out. Peak expiratory flow (PEF) measures the maximum speed at which air is forcefully expired (litres per second). The forced expiratory volume 1 (FEV1) is the amount of air that is forcibly blown out within the first second of the test.

Plotting the FVC and PEF values generates a spirograph similar to the one shown in Video 7. The FEV1/FVC ratio (also calculated as a percentage) is used to evaluate lung function. In healthy individuals, the FEV1/FVC ratio is approximately 0.8, meaning that 80% of total volume of air is blown out within the first second.

Described image
Figure 10 Portable spirometer used to measure lung function.

It is important to note that normal lung function is dependent on an individual’s age, height, sex, ethnicity and general fitness. An example of the predicted FEV1/FVC ratios for particular groups of men and women is shown in Table 1.

Table 1 Predicted FEV1/FVC ratios for asymptomatic, lifelong non-smoker Caucasian men and women over the lifespan.

FEV1/FVC (%) Male
Age 20 25 30 35 40 45 50 55 60 65 70 75 80
All heights 83.9 82.9 81.9 80.8 79.8 78.8 77.7 76.7 75.7 74.6 73.6 72.6 71.5
FEV1/FVC (%) Female
Age 20 25 30 35 40 45 50 55 60 65 70 75 80
All heights 86.6 85.5 84.4 83.4 82.3 81.2 80.2 79.1 78.1 77.0 75.9 74.9 73.8

Question 7 Lung function across ages

Looking at Table 1, what happens to lung function with age in both men and women?


It stays the same across all ages.


It increases with age.


It decreases with age.

The correct answer is c.


Correct. Lung function, as measured by the FEV1/FVC percentage, decreases with age in both men and women.


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