754
UNIT FIVE
Nonrespiratory Air Movements
Air movements other than breathing are called
nonrespira-
tory movements.
They clear air passages, as in coughing and
sneezing, or express emotions, as in laughing and crying.
Nonrespiratory movements usually result from
refl
exes,
although sometimes they are initiated voluntarily. A cough,
for example, can be produced through conscious effort or
may be triggered by a foreign object in an air passage.
Coughing
involves taking a deep breath, closing the glot-
tis, and forcing air upward from the lungs against the clo-
sure. Then the glottis is suddenly opened, and a blast of air is
forced upward from the lower respiratory tract. Usually this
rapid rush of air is of sufF cient force to dislodge the object
that triggered the refl
ex.
The most sensitive areas of the air passages are in the larynx, the
carina, and in regions near the branches of the major bronchi. The
distal portions of the bronchioles (respiratory bronchioles), alveo-
lar ducts, and alveoli lack a nerve supply. Consequently, before any
material in these parts can trigger a cough reF
ex, it must be moved
into the larger passages of the respiratory tract.
A
sneeze
is much like a cough, but it clears the upper
respiratory passages rather than the lower ones. Usually a
mild irritation in the lining of the nasal cavity forces a blast
of air up through the glottis. The air is directed into the
nasal passages by depressing the uvula, closing the opening
between the pharynx and the oral cavity.
In
laughing,
a person takes a breath and releases it in a
series of short expirations.
Crying
consists of similar move-
ments, and sometimes it is necessary to note a person’s facial
expression to distinguish laughing from crying.
A
hiccup
is caused by sudden inspiration due to a spas-
modic contraction of the diaphragm while the glottis is
closed. Air striking the vocal folds causes the sound of the
hiccup. We do not know the function, if any, of hiccups.
Alveolar Ventilation
The volume of new atmospheric air moved into the respira-
tory passages each minute is called the
minute ventilation.
It equals the tidal volume multiplied by the breathing rate.
Thus, if the tidal volume is 500 mL and the breathing rate
is 12 breaths per minute, the minute ventilation is 500 mL
×
12, or 6,000 mL per minute. However, for each breath much
of the new air remains in the physiologic dead space.
±or each respiratory cycle, the volume of new air that
does reach the alveoli and is available for gas exchange is
calculated by subtracting the physiologic dead space (150
mL) from the tidal volume (500 mL). The resulting vol-
ume (350 mL) multiplied by the breathing rate (12 breaths
per minute) is the
alveolar ventilation rate
(4,200 mL per
minute). This is the more important value physiologically
because it affects the concentrations of oxygen and carbon
dioxide in the alveoli and thus in the blood.
FIGURE 19.27
A spirometer measures respiratory air volumes.
TABLE
19.4
|
Respiratory Air Volumes and Capacities
Name
Volume
*
Description
Tidal volume (TV)
500 mL
Volume moved in or out of the lungs during a respiratory cycle
Inspiratory reserve volume (lRV)
3,000 mL
Volume that can be inhaled during forced breathing in addition to resting tidal volume
Expiratory reserve volume (ERV)
1,100 mL
Volume that can be exhaled during forced breathing in addition to resting tidal volume
Residual volume (RV)
1,200 mL
Volume that remains in the lungs at all times
Inspiratory capacity (IC)
3,500 mL
Maximum volume of air that can be inhaled following exhalation of resting tidal volume:
IC = TV + lRV
±unctional residual capacity (±RC)
2,300 mL
Volume of air that remains in the lungs following exhalation of resting tidal volume:
±RC = ERV + RV
Vital capacity (VC)
4,600 mL
Maximum volume of air that can be exhaled after taking the deepest breath possible:
VC = TV + IRV + ERV
Total lung capacity (TLC)
5,800 mL
Total volume of air that the lungs can hold: TLC = VC + RV
*
Values are typical for a tall, young adult.
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