1. Lung Volumes and Capacities
Measurement of lung volumes provides a tool for understanding normal function of the lungs as
well as disease states. The breathing cycle is initiated by expansion of the chest. Contraction of
the diaphragm causes it to flatten downward. If chest muscles are used, the ribs expand outward.
The resulting increase in chest volume creates a negative pressure that draws air in through the
nose and mouth. Normal exhalation is passive, resulting from “recoil” of the chest wall,
diaphragm, and lung tissue.
Tidal Volume (TV): The volume of air breathed in and out without
conscious effort
Inspiratory Reserve Volume (IRV): The additional volume of air that can be inhaled with
maximum effort after a normal inspiration
Expiratory Reserve Volume (ERV): The additional volume of air that can be forcibly
exhaled after normal exhalation
Vital Capacity (VC): The total volume of air that can be exhaled after a
maximum inhalation: VC = TV + IRV + ERV
Residual Volume (RV): The volume of air remaining in the lungs after
maximum exhalation (the lungs can never be
completely emptied)
Total Lung Capacity (TLC): = VC + RV
Minute Ventilation: The volume of air breathed in 1 minute: (TV)(breaths/minute)
DATA
Table 1
Class average Class average
Volume measurement
Individual (L) (Male) (Female)
(L)
(L) (L)
Tidal Volume (TV) .2 .4 .2
Inspiratory Reserve (IRV) .5 .6 .4
Expiratory Reserve .4 .4 .3
(ERV)
Vital Capacity (VC) 1.1 1.6 1.2
Residual Volume (RV) ≈1.5 ≈1.5 ≈1.5
Total Lung Capacity 2.6 2.6 2.4
(TLC)
2. DATA ANALYSIS
1. What was your Tidal Volume (TV)? What would you expect your TV to be if you inhaled a
foreign object which completely obstructed your right mainstem bronchus?
TV - .2
If you inhaled a foreign object and completely obstructed your right mainstem bronchus
your TV will become half because only your left will function.
2. Describe the difference between lung volumes for males and females. What might account
for this?
Males have a larger lung capacity, which enables them to take in more air than women.
This might be because men have larger torsos than females, which lungs might be
larger.
3. Calculate your Minute Volume at rest.
(TV × breaths/minute) = Minute Volume at rest
If you are taking shallow breaths (TV = 0.20 L) to avoid severe pain from rib fractures, what
respiratory rate will be required to achieve the same minute volume?
(.2 x 15) = 3 MV
4. Exposure to occupational hazards such as coal dust, silica dust, and asbestos may lead to
fibrosis, or scarring of lung tissue. With this condition, the lungs become stiff and have more
“recoil.” What would happen to TLC and VC under these conditions?
When exposed to occupational hazards the Total Lung Capacity and Vital Capacity will
decrease because there will be more recoil in the lunch and with the lungs stiffened it
will be harder to breathe. The breathing rate will increase to compensate for the loss of
air.
5. In severe emphysema there is destruction of lung tissue and reduced recoil. What would you
expect to happen to TLC and VC?
In serve emphysema, one’s Total Lung Capacity will remain the same but the Vital
Capacity will decrease recoil because they can’t contract easily, causing breathing
problems.
6. What would you expect to happen to your Expiratory Reserve Volume when you are treading
water in a lake?
Your Expiratory Reserve Volume when you are treading water in a lake will increase
because you are taking in more oxygen to help you tread across the lake.
4. Minute ventilation (L/min) 3.2
DATA ANALYSIS
1. Describe the changes in respiratory rates, tidal volumes, and minute ventilations that
occurred after each of the following physiologic challenges in terms of CO2 levels and their
effect on respiratory drive:
(a) breath holding – After holding your breath the tidal volume, respiratory rate, and
minute ventilation was lower than it was before.
(b) rapid breathing – After rapid breathing the tidal volume, respiratory rate, and
minute ventilation was higher than it was before with normal breathing.
(c) exercise – After exercise the tidal volume, respiratory rate, and minute ventilation
increase and was higher than before without the exercise.
2. Which challenge caused the greatest change in respiratory rate (pre-challenge vs. post
challenge)? Tidal volume? Minute ventilation? Did respiratory rate or tidal volume change
the most relative to its resting value?
The greatest change in respiratory rate was when he was rapid breathing. The greatest
change in tidal volume was holding breath. And the greatest change in minute
ventilation was rapid breathing. The tidal volume changed the most from what its
resting value was.
3. How might breathing into a paper bag help someone who is extremely anxious and
hyperventilating?
Breathing into a paper bag can help someone who is anxious and hyperventilating because
when they breathe into the bag and exhale into the bag the levels of CO2 are increased
in the bag, and it helps bring more CO2 into the body and bloodstream and make your
PH normal.
4. Some patients with severe emphysema have constant high levels of CO2 because of
inadequate ventilation. The central nervous system breathing center in these patients becomes
insensitive to CO2 and more dependent on the level of O2, which is low. These patients are
said to have “oxygen-dependent respiratory drive.” What might happen if you give such a
person high levels of supplemental O2?
If you give them high levels of O2 it should help balance out the need for both CO2 and O2,
making the oxygen-dependent state slowly go away.
5. Would breathing pure O2 help the air hunger experienced by athletes who have just
completed a race? Why or why not?
Breathing pure O2 after a race doesn’t help athletes any more than just breathing the
regular air afterwards. They are feeling the air hunger because of the overuse of their
muscles causing a buildup of lactic acid in the muscles and blood.
