RESPIRATION
Respiration includes:
(1) pulmonary ventilation, the entrance and exit of gasses into and out
of the lungs
(2) external respiration, exchange of O2 and CO2 between the air and
the blood
(3) internal respiration, the exchange of O2 and CO2 between the blood
and tissues
(4) cellular respiration, the production of ATP (in the presence of O2) in
body cells.
In this laboratory exercise, we will be concerned primarily with
pulmonary ventilation (breathing).
Respiratory anatomy
Several figures in your text will assist you in identifying the key
structural elements of the respiratory system. Use Figure 9.2, an
anterior (front) view of the respiratory tract, and Figures 9.3 and 9.5 as
you examine the plastic model of the human torso.
Identify the following structures and consider the questions:
Trachea: This tube conducts air from the pharynx (back of nose and
mouth) to the bronchi.
Does the trachea lie anterior or posterior to the esophagus, the
tube through which food passes to the stomach?
How do the trachea and esophagus differ in appearance?
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Bronchi: These major airways conduct air from the trachea to the
lungs.
In anatomy, right (R) and left (L) are always determined from the
point of view of the subject, not the observer. With this in mind, identify
the L main bronchus and R main bronchus.
Bronchioles and alveoli: These are the smaller airways and the
clustered, terminal gas exchange sacs. (These must be seen on the
lung cast, not the plastic torso.)
Lungs: These are the major gas exchange organs.
Examine the L and R lungs; notice that they are segmented into
lobes or major divisions.
How many lobes does each lung possess?
Left __________
Right __________
Are the lungs the same size?
Consider the fact that the heart lies to the L in the thoracic cavity. Do
the number of lobes and the relative sizes of the L and R lungs seem
reasonable?
Pulmonary arteries: These blood vessels conduct deoxygenated
blood from the heart to the lungs.
Pulmonary veins: These conduct oxygenated blood from the lungs to
the heart.
Diaphragm: This major muscle at the base of the thoracic cavity
contracts to draw air into the lungs.
When the diaphragm contracts, does it move up or down?
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Ribs and sternum: These bones surround the thoracic cavity. (These
must be seen on the skeleton model.)
Where do the ribs originate?
How are the ribs connected to the sternum?
How does the rib cage move when you inhale? exhale?
Label the following photograph:
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An exercise in respiratory physiology
Respiratory function is most easily assessed by the use of
handheld or bell spirometers. Each spirometer has a meter that
measures the volume of air that has been exhaled into the spirometer.
The large bell spirometers measure lung volumes in liters whereas the
handheld spirometers use milliliters as the units of measure. You will be
reporting the volumes as liters therefore the milliliter measurements
must be divided by 1,000 to obtain a liter value. In addition, the
handheld spirometers operate by a small flywheel; in order to turn this
flywheel you may have to exhale in a sharper, quicker fashion than
normal. Record the data on the appropriate line of your lab manual. Use
the instructions below to measure 4 different lung volumes
Tidal Volume (TV): Inhale a volume of air into your lungs that you
would with a normal average breath. Exhale into the mouthpiece of the
spirometer and stop exhaling at the level that you would when taking a
normal breath. Record the data in liters on the TV line. The normal TV
is around 0.5 liters of air. TV______________ liters
Inspiratory Reserve Volume (IRV): Inhale as much air as you can into
your lungs. Exhale into the mouthpiece of the spirometer and stop
exhaling at the level that you would when taking a normal breath.
Record the data in liters on the IRV line. The normal IRV is around 3.1
liters of air.
IRV_________________liters
Expiratory Reserve Volume (ERV): Inhale a volume of air into your
lungs that you would with a normal average breath. Exhale to a level
that you would in a normal breath. Now exhale as much as you can into
the mouthpiece of the spirometer. Record the data in liters on the ERV
line. The normal ERV is around 1.2 liters of air.
ERV___________liters
Forced Vital Capacity (FVC): Inhale as much air as you can into your
lungs. Place the mouthpiece up to you lips and exhale as much as you
can into the spirometer. Record the data in liters on the FVC line. The
normal ERV is around 4.8 liters of air. FVC___________liters
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Let's see how well you've done. The graphs shown below allow
you to determine the expected FVC for your age, sex, and height. Draw
a line on the appropriate graph (male or female) from your age upward
to your height line. From there, go across to the Y-axis to read your
expected FVC. As an example, the method is illustrated for a female,
age 25, height 64", yielding an expected FVC of 3.9 liters.
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If your actual FVC is lower than the expected value, think about
factors which might be reducing your respiratory performance Do you smoke? Do you get adequate/inadequate exercise?
If you think about what you did in measuring your forced vital
capacity (FVC), you will realize it is the sum of other three
operations (IRV, TV, and ERV). Thus, the sum of IRV+TV+ERV
should be close to the FVC. Check to see whether this is true.
IRV + TV + ERV = __________ liters
FVC = __________ liters
In normal breathing, we typically use only 10-15% of our vital
capacity. There is a tremendous reserve capacity. Verify that your tidal
volume (normal breathing) is about 10-15% of your FVC.
Tidal volume x 100% = __________ = ________ %
Forced vital capacity
Finally, some air always remains in the lungs to prevent their
collapse. You can't force it out, so it's not measured by the FVC test.
For most of us, this residual volume (RV) is about 1/3 of the FVC.
Assuming this is true, calculate your RV and total lung capacity (TLC),
the sum of the FVC and RV.
RV = 1/3 x FVC = __________ liters
TLC = FVC + RV = _________ liters
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The Control of Breathing
The objective of this exercise is to examine factors that determine
the duration of a breath hold.
Breathing functions to ventilate our lungs, adding oxygen (O2) and
removing carbon dioxide (CO2) in the process. An individual's
ventilation rate originates from neuronal "pattern generators" in the
brainstem. These pattern generators receive stimulatory input from
mechanoreceptors in the lungs and chest wall, and CO2 and O2
chemoreceptors in the brain and arterial blood vessels. In addition to
these reflexes, breathing rate is under conscious control of higher brain
centers.
In humans (and all other terrestrial animals), the concentration of
CO2 in the brain and blood is the primary stimulus that affects breathing
rate. The CO2 concentration in expired air at the "breaking point" of a
breath hold is, therefore, a very consistent index of the maximum
duration of the breath hold. In other words, the duration of a breath hold
is determined mainly by how long it takes to reach the body's upper CO2
set-point for each individual.
Factors affecting breath holding
Students should work in pairs or small groups. Each student
should perform all the exercises. Work with another student who should
run the stopwatch to time your breath holding. In each exercise, hold
your breath for as long as possible. DO NOT time yourself (Can you
see why someone else should time your breath holding?), and DO NOT
engage in competitions with classmates! Allow at least 5 minutes
between each exercise for recovery. DO NOT perform these exercises
until you have completed the basic respiration laboratory. Remember to
perform all exercises while sitting down.
1. Slowly breath in as much air as you can, then hold your breath. This
point is your total lung capacity (TLC), which, as you know, is equal to
your forced vital capacity (FVC) plus your residual volume (RV). Record
your breath holding time (in seconds) in the Table as TLC#1.
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2. Slowly breath in as much air as you can. Exhale normally to a
relaxed volume, then hold your breath. This is your functional residual
capacity (FRC), which is equal to your expiratory reserve volume (ERV)
plus your RV. Record your breath holding time (in seconds) in the Table
as FRC#1.
3. Repeat exercise 1 for TLC; record the result as TLC#2.
4. Repeat exercise 2 for FRC; record the result as FRC#2.
5. Hyperventilate for 30 seconds (NO LONGER; sit down before you
begin this exercise!). Begin breath holding at the FRC. Record your
breath holding time (in seconds) in the Table as HYPERVENT.
6. Begin holding your breath at the FRC. At the breaking point (when
you cannot hold your breath any longer), exhale into a reservoir bag and
immediately inhale the exhaled air. Continue to hold your breath to the
next breaking point. Repeat this procedure as many times as possible
until you simply cannot hold your breath after rebreathing the air.
Record your breath holding times (in seconds) in the Table as
REBREATHING. Add these times together to get your total breath
holding duration for this exercise and record this value in the Table.
7. Begin holding your breath at the FRC and hold your breath while
squeezing a handgrip. Record the breath holding time (in seconds) in
the Table as HAND EXERCISE.
8. Repeat exercise 1 for TLC; record the result as TLC#3.
9. Repeat exercise 2 for FRC; record the result as FRC#3.
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RESULT TABLE
Exercise
Breath holding duration (secs)
TLC#1
__________________________
FRC#1
__________________________
TLC#2
__________________________
FRC#2
__________________________
HYPERVENT
__________________________
REBREATHING
__________________________
HAND EXERCISE
__________________________
TLC#3
__________________________
FRC#3
__________________________
Interpretation of results
1. Does the starting volume of air in the lungs affect the breath holding
duration? Explain your answer based on your results and those of your
group mates with the TLC and FRC exercises.
2. Were the second and third TLC and FRC breath hold times longer or
shorter than the first trials? Explain any difference.
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3. Why does hyperventilation increase breath holding time? What is
the stimulus that makes us stop the breath hold?
4. Did exhaling into the bag increase or decrease the total breath hold
duration? Explain your answer.
5. Why was there a difference in the breath hold duration when you
started holding your breath at FRC but squeezed a handgrip? Compare
the time of this exercise with the second and third FRC trials.
Internet Resources
The “Virtual Hospital” has a tutorial on lung anatomy; check
http://www.vh.org/adult/provider/radiology/LungAnatomy/LungAnatomy.
html.
To learn about more about the lungs and lung diseases, connect
to the American Lung Association site at http://www.lungusa.org.
A general review of respiratory physiology and the specific
problems associated with scuba diving can be found at
http://www.mtsinai.org/pulmonary/books/scuba/contents.htm.
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