Ganong's Review of Medical Physiology, 23rd Edition

LUNG VOLUMES
The amount of air that moves into the lungs with each inspiration
(or the amount that moves out with each expiration) is
called the tidal volume. The air inspired with a maximal inspiratory
effort in excess of the tidal volume is the inspiratory reserve
volume. The volume expelled by an active expiratory effort after
passive expiration is the expiratory reserve volume, and the air
left in the lungs after a maximal expiratory effort is the residual
volume. Normal values for these lung volumes, and names applied
to combinations of them, are shown in Figure 35–7. The
space in the conducting zone of the airways occupied by gas that
does not exchange with blood in the pulmonary vessels is the
respiratory dead space. The forced vital capacity (FVC), the
RV
ERV
TV
IRV
Dead space
Expiration Lung volume (ml) Inspiration
6000
5000
4000
3000
2000
1000
0
Maximum possible inspiration
2
Inspiratory reserve
volume
1 Tidal volume
Maximum
voluntary
expiration
CHAPTER 35 Pulmonary Function 593
largest amount of air that can be expired after a maximal inspiratory
effort, is frequently measured clinically as an index of pulmonary
function. It gives useful information about the strength
of the respiratory muscles and other aspects of pulmonary function.
The fraction of the vital capacity expired during the first
second of a forced expiration is referred to as FEV 1 (formerly the
timed vital capacity) (Figure 35–8). The FEV 1 to FVC ratio
(FEV 1/FVC) is a useful tool in the diagnosis of airway disease
(Clinical Box 35–1). The amount of air inspired per minute
(pulmonary ventilation, respiratory minute volume) is normally
about 6 L (500 mL/ breath × 12 breaths/min). The maximal
voluntary ventilation (MVV) is the largest volume of gas
that can be moved into and out of the lungs in 1 min by voluntary
effort. The normal MVV is 125 to 170 L/min.
3
Expiratory reserve volume
4
Residual volume
5 Vital
capacity
Functional residual capacity
7
Respiratory Volumes and Capacities for an Average Young Adult Male
FIGURE 35–7 Lung volumes and capacity measurements. Top left: A cartoon figure representing lung space divided into lung volumes.
Dead space refers to areas where gas exchange does not occur; all other spaces are defined in the accompanying table. Top right: Spirometer
recordings are shown with marked lung volumes and capacities. Table at bottom defines individual measurements and values from the top
graphs. Note that residual volume, total lung capacity, and function residual capacity cannot be measure with a spirometer. (Right figure reproduced
with permission from Widmaier EP, Raff H, Strang KT: Vander’s Human Physiology: The Mechanisms of Body Function, 11th ed. McGraw-Hill, 2008.)
6
Inspiratory
capacity
8
Total lung capacity
Measurement
Typical Value
Definition
Respiratory Volumes
1 Tidal volume (TV)
500 ml Amount of air inhaled or exhaled in one breath during relaxed, quiet breathing
2 Inspiratory reserve volume (IRV) 3000 ml Amount of air in excess of tidal inspiration that can be inhaled with maximum effort
3 Expiratory reserve volume (ERV) 1200 ml Amount of air in excess of tidal expiration that can be exhaled with maximum effort
4 Residual volume (RV)
1200 ml Amount of air remaining in the lungs after maximum expiration; keeps alveoli inflated
between breaths and mixes with fresh air on next inspiration
Respiratory Capacities
5 Vital capacity (VC) 4700 ml Amount of air that can be exhaled with maximum effort after maximum inspiration
(ERV + TV + IRV); used to assess strength of thoracic muscles as well as
pulmonary function
6 Inspiratory capacity (IC)
3500 ml Maximum amount of air that can be inhaled after a normal tidal expiration (TV + IRV)
7 Functional residual capacity (FRC) 2400 ml Amount of air remaining in the lungs after a normal tidal expiration (RV + ERV)
8 Total lung capacity (TLC)
5900 ml Maximum amount of air the lungs can contain (RV + VC)