822
UNIT 4
Maintenance of the Body
22
Respiratory Capacities
Te
respiratory capacities
include inspiratory, functional re-
sidual, vital, and total lung capacities (Figure 22.16). Te respi-
ratory capacities always consist of two or more lung volumes.
Inspiratory capacity (IC)
is the total amount of air that can
be inspired a±er a normal tidal volume expiration, so it is the
sum of ²V and IRV.
Functional residual capacity (FRC)
represents the amount
of air remaining in the lungs a±er a normal tidal volume ex-
piration and is the combined RV and ERV.
Vital capacity (VC)
is the total amount of exchangeable air.
It is the sum of ²V, IRV, and ERV. In healthy young males,
VC is approximately 4800 ml.
Inspiratory
reserve volume
3100 ml
Tidal volume 500 ml
Milliliters (ml)
Respiratory
volumes
Respiratory
capacities
(a) Spirographic record for a male
(b) Summary of respiratory volumes and capacities for males and females
0
1000
2000
3000
4000
5000
6000
Expiratory
reserve volume
1200 ml
Residual volume
1200 ml
Functional
residual
capacity
2400 ml
Inspiratory
capacity
3600 ml
Vital
capacity
4800 ml
Total lung
capacity
6000 ml
Tidal volume (TV)
Amount of air inhaled or exhaled with each breath under resting
conditions
3100 ml
Inspiratory reserve
volume (IRV)
Expiratory reserve
volume (ERV)
Functional residual
capacity (FRC)
Volume of air remaining in the lungs after a normal tidal volume
expiration: FRC = ERV + RV
Maximum amount of air contained in lungs after a maximum
inspiratory effort: TLC = TV + IRV + ERV + RV
Maximum amount of air that can be expired after a maximum
inspiratory effort: VC = TV + IRV + ERV
Maximum amount of air that can be inspired after a normal tidal
volume expiration: IC = TV + IRV
Residual volume (RV)
Amount of air remaining in the lungs after a forced expiration
Total lung capacity (TLC)
Vital capacity (VC)
Inspiratory capacity (IC)
500 ml
Amount of air that can be forcefully inhaled after a normal tidal
volume inspiration
Amount of air that can be forcefully exhaled after a normal tidal
volume expiration
1200 ml
1200 ml
6000 ml
4800 ml
3600 ml
2400 ml
Measurement
Description
Adult male
average value
1900 ml
500 ml
700 ml
1100 ml
4200 ml
3100 ml
2400 ml
1800 ml
Adult female
average value
Figure 22.16
Respiratory volumes and capacities.
Idealized spirographic record of
respiratory volumes in (a) is for a healthy young 70-kg adult male.
Total lung capacity (TLC)
is the sum of all lung volumes and
is normally around 6000 ml.
As indicated in Figure 22.16b, lung volumes and capacities (with
the possible exception of ²V) tend to be smaller in women than
in men because of women’s smaller size.
Dead Space
Some of the inspired air fills the conducting respiratory pas-
sageways and never contributes to gas exchange in the alveoli.
Te volume of these conducting zone conduits, which make up
the
anatomical dead space
, typically amounts to about 150 ml.
(Te rule of thumb is that the anatomical dead space volume in
a healthy young adult is equal to 1 ml per pound of ideal body
weight.) Tis means that if ²V is 500 ml, only 350 ml of it is
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