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Figure 12.18 shows four points on the flow–volume diagram of the lungs of a healthy young man. W is the lung volume at total lung capacity and Y is the lung volume at residual volume. Z and X represent maximal outflow and maximal inflow respectively. The person has breathed in and out a vital capacity as quickly as possible. For each of descriptions a–e below, select the best option from the following list of points, lines and areas.
1. W
2. X
3. Y
4. Z
5. WZ
6. ZW
7. ZY
8. YZ
9. WX
10. XW
11. XY
12. YX
13. ZX
14. XZ
15. Totally inside the loop below.
16. Partially outside the loop below
- The line which corresponds most closely to the first part of a forced expiratory volume in one second manoeuvre.
- The point at which lung volume is closest to one litre.
- The position of the loop during strenuous exercise in the same person.
- The final part of the manoeuvre of measuring a fast vital capacity.
- The point at which intra-alveolar pressure is likely to be most negative.
Medicine
a. Option 5 WZ. The manoeuvre starts at total lung capacity and the volume expired in the first second is measured.
b. Option 3 Y. The residual volume of a healthy young man is usually a little over a litre.
c. Option 15 Totally inside the loop. Although volumes and flows increase with exercise, they are still below the maximal; the loop for tidal breathing is smaller still.
d. Option 7 ZY. After the first second of rapid expiration the person must continue breathing out until residual volume is reached, usually in a further second or two.
e. Option 2 X. This is the point of maximal inflow; at this point the pressure gradient between atmosphere and alveoli is also maximal, with alveolar pressure subatmospheric.
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