544 Chapter 16
the volume of air in the dead space is an anatomical constant,
the percentage of fresh air entering the alveoli is increased with
increasing tidal volumes. For example, if the anatomical dead
space is 150 ml and the tidal volume is 500 ml, the percentage of
fresh air reaching the alveoli is 350/500 3 100% 5 70%. If the
tidal volume is increased to 2,000 ml, and the anatomical dead
space is still 150 ml, the percentage of fresh air reaching the
alveoli is increased to 1,850/2,000 3 100% 5 93%. An increase
in tidal volume can thus be a factor in the respiratory adaptations
to exercise and high altitude.
Restrictive and Obstructive Disorders
Spirometry is useful in the diagnosis of lung diseases. On the
basis of pulmonary function tests, lung disorders can be classi-
fied as restrictive or obstructive. In restrictive disorders, such
as pulmonary fibrosis, the vital capacity is reduced to below nor-
mal. The rate at which the vital capacity can be forcibly exhaled,
however, is normal. In disorders that are exclusively obstruc-
tive, by contrast, the vital capacity is normal because lung tis-
sue is not damaged. In asthma, for example, the vital capacity is
usually normal but expiration is more difficult and takes a longer
time because bronchoconstriction increases the resistance to air
flow. Obstructive disorders are therefore diagnosed by tests
that measure the rate of expiration. One such test is the forced
expiratory volume (FEV), in which the percentage of the vital
capacity that can be exhaled in the first second (FEV 1 ) is mea-
sured ( fig. 16.16 ). An FEV 1 that is significantly less than 80%
suggests the presence of obstructive pulmonary disease.Pulmonary Disorders
People with pulmonary disorders frequently complain of
dyspnea, a subjective feeling of “shortness of breath.” Dys-
pnea may occur even when ventilation is normal, however, and
may not occur even when total minute volume is very high, as
in exercise. Some of the terms associated with ventilation are
defined in table 16.4.Table 16.4 | Ventilation Terminology
Term Definition
Air spaces Alveolar ducts, alveolar sacs, and alveoli
Airways Structures that conduct air from the mouth
and nose to the respiratory bronchiolesAlveolar ventilation Removal and replacement of gas in alveoli;
equal to the tidal volume minus the volume
of dead space times the breathing rate
Anatomical dead
spaceVolume of the conducting airways to the zone
where gas exchange occurs
Apnea Cessation of breathing
Dyspnea Unpleasant, subjective feeling of difficult or
labored breathing
Eupnea Normal, comfortable breathing at rest
Hyperventilation Alveolar ventilation that is excessive in relation
to metabolic rate; results in abnormally low
alveolar CO 2
Hypoventilation Alveolar ventilation that is low in relation to
metabolic rate; results in abnormally high
alveolar CO 2
Physiological dead
spaceCombination of anatomical dead space and
underventilated or underperfused alveoli
that do not contribute normally to blood
gas exchange
Pneumothorax Presence of gas in the intrapleural space (the
space between the visceral and parietal
pleurae) causing lung collapse
Torr Unit of pressure nearly equal to the millimeter
of mercury (760 mmHg 5 760 torr)Figure 16.16 The one-second forced expiratory
volume (FEV 1 ) test. The percentage in ( a ) is normal, whereas
that in ( b ) may indicate an obstructive pulmonary disorder such
as asthma or bronchitis.2.5 L1.8 L1.0
second(b) (a)Maximum expiration = 1 LMaximum inspiration = 5 L(a) FEV 1 = 5 L–1.8 L x 100% = 80%(b) FEV 1 = 5 L–2.5 L x 100% = 62.5%5 L–1 L5 L–1 LFITNESS APPLICATION
Cigarette smoking has been found to promote obstructive
lung disorders as measured by a reduced FEV 1 , even among
people who otherwise appear to have no symptoms. For
example, the FEV 1 normally declines with age, but the age-
related decline is accelerated in smokers. However, the rate
of decline is reduced in people who quit smoking compared
to those who continue to smoke. Also, the rate of decline in
smokers with mild COPD (discussed shortly) who quit was
found to be less than in those who continued to smoke. Air
pollution has also been found to significantly affect the FEV 1
of children with asthma, and other studies have suggested
that it may be unhealthy to exercise on very smoggy days.