Respiratory System Chapter 23

Pulmonary Volumes and Capacities

FIGURE 23.15

1. A spirometer is a device for measuring the volumes of air that move into and out of the respiratory system. Spirometry is the process of taking the measurements. 2. There are four pulmonary volumes. A. Tidal volume is the amount of air that moves in or out of the respiratory system during normal, quiet, at rest breathing. B. Inspiratory reserve is the amount of air that can be taken into the lungs following a normal tidal volume. It is the amount of air "on top" of the tidal volume. C. Expiratory reserve is the amount of air that can be forced out of the lungs following a normal tidal volume. It is the amount of air "below" the tidal volume. D. Residual volume is the amount of air that remains in the lungs after the expiratory reserve. It is the volume of air that cannot be eliminated from the lungs. E. Pulmonary volumes for a young adult male: Tidal volume 500 mL Inspiratory reserve 3000 mL Expiratory reserve 1100 mL Residual volume 1200 mL 3. A pulmonary capacity is two or more pulmonary volumes added together. A. Inspiratory capacity is tidal volume plus inspiratory reserve. This is the amount of air a person can inspire after a normal expiration. B. Functional residual capacity is the expiratory reserve volume plus the residual volume. This is the amount of air in the lungs after a normal expiration. C. Vital capacity is the expiratory reserve plus the tidal volume plus the inspiratory reserve. It is the air a person can expel from the lungs after taking as deep a breath as possible. D. Total lung capacity is the sum of the four pulmonary volumes. E. Pulmonary capacities for a young adult male: Inspiratory capacity 3500 mL Functional residual capacity 2300 mL Vital capacity 4600 mL Total lung capacity 5800 mL

23-1 4. Using the spirometer, it is reasonably easy to measure vital capacity, tidal volume, and expiratory reserve. Inspiratory reserve is usually calculated using these measurements. IR = VC - (TV + ER)

☞ Practice problem: Marty Blowhard used a spirometer with the following results: a. After a normal inspiration, a normal expiration was 500 mL. b. Following a normal expiration, he was able to expel an additional 1000 mL. c. Taking as deep a breath as possible then forcefully exhaling all the air possible, yielded an output of 4500 mL. On the basis of these measurements, what is Marty's inspiratory reserve?

☞ Practice problem: Explain who would be most likely to have the greatest vital capacity? A. A young adult male versus a female of the same age.

B. A man standing and the same man lying down.

C. A healthy man and a man of the same size and age who has muscular dystrophy.

23-2 D. A healthy man and a man of the same size and age who has emphysema.

5. Forced expiratory vital capacity determines the rate at which the lungs empty during a vital capacity measurement. A. In some conditions vital capacity is not significantly affected, but the rate at which air can be expelled is reduced. B. Examples include airway obstruction from asthma or a tumor that blocks the bronchi.

Minute Ventilation and Alveolar Ventilation 1. The minute ventilation is the total amount of air moved into and out of the lungs in a minute. Minute ventilation (MV) is equal to the tidal volume (TV) times the respiratory rate (RR; breaths/min): MV = TV x RR = 500 mL/breath x 12 breaths/min = 6000 mL/min =6 L/min 2. Minute ventilation does not measure the amount of air available for gas exchange, because gas exchange does not occur everywhere within the lungs.

3. The dead space (VD) is the part of the respiratory system in which gas exchange does not take place. A. The anatomic dead space is the air within the conducting zone of the tracheobronchial tree. This air is not available for gas exchange. A typical value is 150 mL of air. B. The physiologic dead space is anatomic dead space plus the air within any alveoli that are not functioning normally. 1) Normally physiologic dead space is equal to the anatomic dead space, which means all of the alveoli are functioning normally.

2) In emphysema, the walls between alveoli are destroyed. Consequently, the surface area available for gas exchange decreases. This can dramatically increase physiologic dead space.

23-3 4. Alveolar ventilation (AV) is a measure of the gas available for gas exchange that takes into account the dead space.

AV = RR (TV - VD)

☞ Practice Problem: If a resting person had a tidal volume of 500 mL, a dead space of 150 mL, and a respiratory rate of 12 breaths/min, what would his alveolar ventilation be? How does this compare to his minute ventilation?

☞ Explain why increasing the respiration rate to 24 breaths/min and tidal volume to 4000 mL during exercise would be beneficial.

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