Lab I
OXYGEN CONSUMPTION
Oxygen consumption (VO2) is the amount of oxygen taken up and utilized by the body
per minute. The oxygen taken into the body at the level of the lungs is ultimately transported by
the cardiovascular system to the systemic tissues and is used for the production of ATP in the
mitochondria of our cells. Because most of the energy in the body is produced aerobically, VO2
can be used to determine how much energy a subject is expending. VO2 can be reported in
absolute terms (L/min) or relative to body mass (ml/kg*min). Oxygen consumption is dependent
on the ability of the heart to pump out blood, the ability of the tissues to extract oxygen from the
blood, the ability to ventilate and the ability of the alveoli to extract oxygen from the air.
At rest, nearly all of the body’s energy demands are being met by aerobic metabolic
processes, which require oxygen. The mitochondria are the site of aerobic metabolism in the
cells (aerobic metabolism will be covered in greater detail in labs later this quarter). Ultimately,
oxygen is the final electron acceptor in the electron transport chain, forming water in the process.
As oxygen is being consumed, carbon dioxide is also being produced, and must be cleared from
the tissues to the blood, and ultimately blown off in the expired air.
There are two general methods of measuring oxygen consumption: (1) the closed circuit
method, and (2) the open circuit method. The open circuit method is the one that we will use in
our labs (it is also the more common method to be used in other exercise labs across the world).
In open circuit spirometry the subject inhales air from the atmosphere, while the exhaled air is
directed into a collection device such as a meteorological balloon, a wet spirometer, or Douglas
bag. The collected air is analyzed to determine the fractional content of expired oxygen (FEO2),
the fractional content of expired carbon dioxide (FECO2), and the volume of air expired (which
will be used to determine the minute ventilation, VE, as we did in the previous lab). FEO2 and
FECO2 are simply the percents (represented in decimal form) of expired air that are oxygen or
carbon dioxide. Once VE, FEO2 and FECO2 have been determined, several calculations are
then made to determine oxygen consumption (and carbon dioxide production, as well as other
calculations).
In addition to determining oxygen consumption using meteorological balloons, gas
analyzers, and volume meters, we will also be determining the VO2 max of each subject in the
class using a metabolic cart. A metabolic cart includes gas analyzers for oxygen and carbon
dioxide, a volume meter or pneumotachograph, a computer, and frequently also requires a
mixing chamber.
The maximal ability of a subject to take up and utilize oxygen is frequently referred to as
their maximum oxygen consumption (VO2max) or aerobic capacity. Because tests evaluating
VO2max stress the oxygen delivery (pulmonary and cardiovascular) systems and the oxygen
consuming (tissues, especially muscle during exercise), VO2max is frequently thought of as
being synonymous with aerobic fitness, and it is one of several strong predictors of endurance
performance.
Oxygen consumption is one of the most commonly assessed variables in the study of
exercise physiology. Knowledge of oxygen consumption permits, not only the precise
determination of energy expenditure (see Aerobic energy cost of activity lab), but also the
measurement of the overall physiological stress imposed by exercise. The procedures are not
difficult, but they do require careful attention to detail. The methods we will be using in today’s
lab have several potential uses: determining metabolic rate, oxygen deficit, excess post exercise
oxygen consumption (EPOC) or for assessing a subject's anaerobic threshold (AT). We will be
dealing with oxygen consumption and maximal oxygen consumption and related variables in
over half of our labs this quarter. Learning these formulas now is very important!
Today we will be evaluating oxygen consumption at rest and during steady state exercise.
Lab I - 1
Figure 1. O2 Deficit & EPOC
1.8
O2 demand
1.5
O2
deficit
VO2 1.2
(L/min)
0.9
0.6
EPOC
0.3
rest VO2
0
-4
-2
0
2
4
6
8
10
12
14
16
18
20
Time (min)
Oxygen Deficit
When exercise begins, aerobic metabolic processes are not producing ATP rapidly enough
to meet the cell's ATP demands. This deficit in aerobic ATP production necessitates the use of
anaerobic metabolism to "pick up the slack" in meeting the cell's ATP demands. Furthermore,
the cardiovascular and pulmonary systems, while they do respond rapidly, they require some
amount of time to increase cardiac output and ventilation. The oxygen deficit is equal to the
oxygen demands of the activity minus the actual oxygen consumption (see Appendix and
textbook for figures). Another way to put it is that the oxygen deficit is the difference between
the oxygen required for a given rate of work (steady state) and the oxygen actually consumed
(see figure 1, appendix, and textbook).
At the onset of exercise the now active muscles can use O2 that is already present in the
body (bound to hemoglobin and myoglobin). That is, these oxygen-binding proteins will partly
and temporarily desaturate to help maintain pO2 and mitochondrial respiration until the body’s
cardiovascular and pulmonary systems increase their activity enough to increase O2 delivery to
the muscles.
Also at the onset of exercise, two major anaerobic energy systems contribute to ATP
production to help maintain cellular ATP homeostasis until aerobic metabolism is able to meet
the ATP demands alone: the phosphocreatine system and anaerobic glycolysis. The simplest and
fastest mechanism of ATP production is the ATP-PC system (also called the phosphagen or
phosphocreatine system). Phosphocreatine (usually abbreviated PC or PCr) is a high energy
compound that can readily "donate" its phosphate group to ADP in order to rapidly produce
ATP. This reaction, which is catalyzed by the enzyme creatine kinase, is summarized below.
ADP & PCr
Creatine Kinase
ATP + Cr
This reaction is reversible and does not require oxygen. During exercise, when ATP is being
used rapidly and ADP concentrations increase, this reaction favors production of ATP at the
expense of PCr. During recovery, the PCr stores must be replenished (which, of course requires
ATP). The ATP-PC system is used at the beginning of any exercise bout, and because it can
Lab I - 2
produce ATP so quickly it is especially important for high intensity exercise lasting less than 10
seconds in duration.
Anaerobic glycolysis also contributes to the maintenance of cellular ATP concentrations
when the cell’s ATP demands are greater than aerobic metabolism is making it. The term
anaerobic means that these systems do not require oxygen. It is a common student
misconception that these systems are only used when the cells are lacking oxygen. This is false.
It is true that if a cell lacks oxygen it will have to rely on anaerobic energy systems to produce
ATP. However, most of the cells in our body typically are able to maintain oxygen
concentrations high enough for normal mitochondrial function; even during high intensity
exercise. In the process of using anaerobic glycolysis a couple of relevant events are occurring:
glycogen stores are being used and lactate is being produced.
There are several ways to determine the oxygen demands of the activity. If the exercise
bout is of low to moderate intensity then the simplest way to determine the oxygen demand is to
measure oxygen consumption during exercise bout and determine the average steady state
oxygen consumption after they have reached steady state. Oxygen deficit can then be calculated
by subtracting each of the oxygen consumption values prior to reaching steady state from the
average steady state oxygen consumption. In the next lab we will use a slightly different
procedure to calculate an "accumulated oxygen deficit", which is a method used to determine
anaerobic capacity. When determining the accumulated oxygen deficit, a series of submaximal
workloads are used to determine the relationship between workload and oxygen consumption.
Once this is known, one can estimate the oxygen consumption for any workload.
In summary, what allows us to maintain cellular energy homeostasis before we are able to
increase oxygen consumption enough to meet the cell’s energy demands? Use of O2 already
stored in the body (bound to hemoglobin and myoglobin), use of phosphocreatine stores, and
anaerobic glycolysis.
Excess Post-Exercise Oxygen Consumption (EPOC)
Following any exercise, oxygen consumption does not immediately decrease back to
resting values (see appendix page 55). This elevated VO2 has traditionally been called oxygen
debt because it was believed that all of this excess oxygen consumption after exercise was
needed to repay the O2 deficit. The term oxygen debt is no longer used because it is now
understood that while some of the excess oxygen consumption is being used to repay the oxygen
deficit, not all of the excess oxygen consumption is used for this purpose. The current term for
this excess oxygen consumption after exercise is EPOC, or excess post-exercise oxygen
consumption . EPOC is the total oxygen consumed above resting values during the recovery
period. It is usually measured until recovery VO2 returns to a resting steady state level.
It was theorized for many years that EPOC was composed of two distinct components; an
initial fast component and a slow component. The initial fast component was thought to
represent the oxygen required to replenish the ATP-PC system and to replenish the hemoglobin
and myoglobin oxygen stores used during the very early stages of exercise. During the
secondary slow component the excess oxygen consumption was thought to be used to remove
accumulated lactic acid from the tissues, by either conversion to glycogen or oxidation to CO2
and H2O, thus providing ATP as a source of energy needed to replenish glycogen stores. While
there is some truth to these theories, there are other reasons why oxygen consumption remains
elevated after exercise, and that is the major reason why the term O2 debt is no longer used.
In summary, why does EPOC exist? In addition to replenishing O2 stores, phosphocreatine
stores, and glycogen stores and clearing lactate, the following factors are also contribute to the
increased O2 consumption during recovery: elevated tissue temperature (Q10 effect), increased
metabolism in cardiac and respiratory muscles, and increased levels of circulating
Lab I - 3
catecholomines (Epinephrine and Norepinephrine from the adrenal gland and sympathetic
neuronal “spillover”). If I were you, it would be a good idea to make these into a list – two lists,
actually; 1. things that contribute to EPOC that are related to “repaying” O2 deficit and 2. things
that contribute to EPOC that are unrelated to “repaying” the O2 deficit.
Other introductory, basic exercise terminology used in the study of exercise physiology
There are a number of terms that we will use throughout the quarter in reference to
exercise or the physiological response to exercise. One term that you should be familiar with is
specificity. Specificity refers to the type of exercise and activity that a subject normally
performs. Whenever possible it is best to test and train a subject the way they will be performing
under normal circumstances. Specificity also can be used to refer to the types of energy systems
(aerobic or anaerobic) that the subject usually uses, the muscle groups used, they environment
they would normally compete in, the speed of movement, etc.
When we refer to the physiological response to exercise we must distinguish between the
physiological response to acute exercise and chronic exercise. The physiological response to
acute exercise refers to what is happening physiologically during a single exercise bout (see
appendix p. 2), whereas the physiological response to chronic exercise refers to how the body
adapts physiologically to exercise training (appendix p. 3). Exercise training (chronic exercise)
can be performed using any mode of exercise. The major factors that influence the physiological
responses to acute or chronic exercise are: intensity, duration, frequency, and recovery.
An exercise bout performed at a low to moderate intensity with a constant workload is
called a steady state exercise bout. This is because during this type of exercise, many
physiological variables reach a steady value and remain at that value for a period of time. On the
other hand, during a graded exercise test, the intensity is increased periodically (e.g. increased
every minute or two), such that the physiological stress on the body is becoming progressively
greater.
Two other terms will be used throughout the quarter, absolute and relative. We will
distinguish between absolute and relative in many different circumstances, making it somewhat
confusing for many students. It is perhaps easiest to explain these terms using a few examples.
Exercise intensity is frequently reported relative to some absolute maximal value. For example,
a subject whose maximal power output is 300 watts who is exercising at an absolute intensity of
150 watts is exercising at a relative intensity of 50% of their maximum. The terms of absolute
and relative are also used in other scenarios. For example if you wanted to compare the power
output during cycling between two subjects of different sizes, it would be difficult to make
comparisons between them. Thus, we frequently report values relative to body mass. The larger
subject would most likely have a larger maximal power output in watts (absolute terms) but may
have the same maximal power output in watts per kg of body mass (relative terms). Oxygen
consumption is a variable that we will usually report in both absolute (liters of oxygen consumed
per minute) and in relative terms (milliliters of oxygen consumed per kilogram of body mass per
minute).
Review appendix pages 33-37, 46-51, and 54 as you read and complete this lab.
Lab I - 4
LABORATORY PROCEDURES
I. Metabolic Cart Demo and Calculation of O2 deficit and EPOC.
A. Following preparation of the metabolic cart the subject will be fitted with head gear,
breathing valve and a nose clip. A heart rate monitor will also be used to determine heart
rate.
B. O2 consumption will be measured during a 5-10 min rest period until a stable base line
has been established.
C. With no warm up permitted, the subject will perform a 10 min work bout at an intensity
that will allow a sub “anaerobic threshold” steady state to be attained.
D. Following this 10 min exercise, O2 consumption will be measured continuously post
exercise until all values have returned to near resting values. This measure will probably
last between 10-30 min depending on aerobic fitness capacity of subject.
E. Using the computer printout, calculate O2 deficit; steady state VO2 - actual exercise VO2
prior to reaching steady state conditions.
F. Using the computer printout, calculate the EPOC; VO2 post ex - rest VO2 at baseline.
G. The size of the EPOC is dependent on the intensity and duration of the exercise.
Complete the second calculation of EPOC with the given data. How does the second
calculation compare the first. How can you explain this difference?
II. Rest and Exercise Gas Collection and Oxygen Consumption Calculations
A. One person should serve as a subject for the resting and two exercise bags.
B. Prepare the air collection equipment. This consists of a one-way respiratory valve, a
rubber mouthpiece, nose clip, a gas collection bag and a flexible hose for joining the
respiratory valve to the collection bag. Take the subject's body weight, in kilograms, and
record this information in the Data Recording Form. Also record the environmental
conditions, as given by your instructor. The subject should be sitting in a chair and
allowed to rest for a period of time before the air collection begins.
C. Evacuate all air from the collection bag. To do this, first remove the respiratory valve and
then turn the three-way valve to open the bag to the atmosphere. Remove any jewelry
with sharp projections from your hands and wrists before handling the balloon to prevent
puncturing it. Gently squeeze the bag and roll it up to force out all of the air. Return the
valve to the closed position as the last bit of air is removed.
D. Connect the one-way valve to the gas collection bag via the connecting hose. Be sure that
the connecting hose is attached to the correct outlet of the respiratory valve; otherwise, the
subject will not be able to breathe. Attach the nose clip firmly and place the mouth piece
between the teeth, with the flange placed between the tongue and lips. YOU MUST
ALWAYS BE SURE THAT THERE ARE NO AIR LEAKS - EVEN VERY SMALL
LEAKS WILL CAUSE GROSS INACCURACIES.
E. Collect air to determine the resting oxygen consumption. After the subject has breathed
through the respiratory apparatus for 30-60 seconds, turn the three-way valve so expired
air enters the collection balloon and start timing the air collection period. PRECISE
Lab I - 5
TIMING IS ESSENTIAL. For the resting collection, collect expired air for 5 minutes and
have the subject count the number of breaths they take for one of those minutes; record
this number as their respiratory rate. Turn the valve closed after exactly 5 minutes. For
exercise gas collections, only collect during the last minutes of the exercise bout and have
your subject count and record their respiratory rate during this minute. . IT IS
IMPORTANT THAT THE SUBJECT BREATHE NORMALLY. THEY MUST NOT
HYPERVENTILATE.
F. While you are collecting the resting gas sample from your subject, obtain the ambient
pressure and temperature information using the barometer and thermometer in the lab.
Also, using established tables (see appendix and table next to thermometer) determine the
pH2O at the current temperature. Record these numbers. They will be used to calculate
the gas correction factors below.
G. Using the gas analyzers, analyze the contents of the bag for O2 and CO2 concentrations
(FEO2 and FECO2) and record FEO2, FECO2 (these should be recorded as a decimal) and
sample volume on the data sheet. The sample volume is the amount of air removed from
the bag by the gas analyzers. These gas analyzers suck air out of the bag at a particular
rate. For example it might be removing air from the bag at a rate of 0.75 Liters of air per
minute. If you were to sample the air for 30 seconds, then the amount of air taken out of
the bag (the sample volume) would be 0.375 Liters. The fractional content of expired
oxygen (FEO2) is the percent of the expired air that is oxygen and the fractional content
of expired carbon dioxide (FECO2) is the percent of expired air that is carbon dioxide.
However, because these are fractions they are usually represented as decimals, not
percentages. The air that we breathe is 20.93% oxygen and 0.03% carbon dioxide.
Humans consume oxygen and produce carbon dioxide, thus the expired air will be less
than 20.93% oxygen and will be more than 0.03% carbon dioxide. Typically the lungs
extract 3-6% percent of the air that is oxygen from the air that enters the lungs. Thus, the
percent of expired air that is oxygen is typically between 15 and 18% (20.93% - 6% 
15% and 20.93% - 3%  18%). Therefore, the FEO2 is usually between 0.15 and 0.18.
Typical values for FECO2 are between 0.025 and 0.06 (i.e. the expired air is between 2.5
and 6% carbon dioxide). It should be noted that if one is extacting oxygen well (good gas
exchange), then their FEO2 will be lower and their FECO2 will be higher. On the other
hand if they do not have very good gas exchange their FEO2 will be higher and their
FECO2 will be lower. The better the gas exchange, the less the subject will need to
ventilate for a given oxygen consumption..
H. After the expired air has been analyzed for O2 and CO2 content, measure its volume.
Remove the connecting hose from the three-way valve and attach it to the inlet on the
volume meter (or gas meter). Be sure to record the initial dial reading from the gas meter
or if possible return the dial to zero. Turn the three-way valve so the collected air goes
into the meter. Squeeze the air out of the meteorological balloon through the gas meter.
When ALL of the air has been removed from the balloon, return the valve to the closed
position. Record the reading from the gas meter as the meter volume. The three way
valve can now be take off of the dry gas meter.
I. After you have collected your resting data and data for both exercise bouts (described
below) open the three-way valve to allow air in the bag to freely exchange with
atmospheric air. This will provide an escape route for moisture which may have collected
in the balloon. This step completes the gas collection and sampling procedures. Clean the
equipment as directed by the laboratory instructor.
Lab I - 6
J. The remaining procedures are calculations based on the data already collected.
1. Take your meter volume measured in the gas meter and add to it the sample volume
used in the determination of O2 and CO2 concentrations to the bag volume to obtain
the ATPS volume (ATPS stands for ambient temperature and pressure saturated, any
time you collect a volume in class you are collecting it in ATPS conditions and you
will need to convert it to STPD or BTPS conditions (see appendix pages 33 to 37)
2. Correct this volume to a per minute value if necessary. The resting gas sample will be
collected over 5 minutes (after adding sample volume divide by 5). The exercise gas
samples will be taken for only the last minute of exercise (so you do not need to divide
by 5).
3. Calculate the BTPS correction Factor. The correction factor that is used to correct for
the difference in volume between ambient and lung (body) conditions is referred to as
the Body Temperature, Pressure, Saturated (or BTPS) correction factor. It not only
corrects for differences in temperature between body (lungs) and ambient conditions,
it also corrects for any differences in pressure and water vapor saturation between
ambient and body conditions. Any time you are reporting a volume of air, and you
want it to represent the amount of air moved by the lungs, it must be reported in BTPS
conditions. Common variables that are reported in BTPS conditions include VE, VC,
TV, MVV. When VE is reported in BTPS conditions we usually refer to it simply as
VEBTPS. The BTPS correction factor can be calculated as follows (A stands for
ambient, T stands for temperature, P stands for pressure, and PH2O stands for water
vapor pressure):
BTPS cf =
310
273 + TA
PA - PH2O
PA - 47
4. Calculate VEbtps. As you learned in your human physiology courses, VE is usually
reported in BTPS conditions. Thus you will need to correct the ATPS volume to a
BTPS volume by using the BTPS correction factor (above, and see appendix). It is
reported in these conditions because when we evaluate VE we are wanting this value
to reflect the volume moved by the lungs per minute.
VEbtps = VEatps x BTPS C. F.
5. Calculate the STPD correction factor. Whether using closed or open spirometry, all
volumes of oxygen consumption and carbon dioxide production must be corrected to
Standard Temperature (0°C) Pressure (760mm Hg) Dry (no water vapor) conditions
(STPD). According to the Ideal Gas Law, under these conditions one liter of any ideal
gas would contain the same number of gas molecules. Thus, under these standard
conditions the volume of any gas (such as oxygen or carbon dioxide) accurately
represents the number of gas molecules. VO2 and VCO2 are always reported in STPD
conditions. Please note that VE is not reported in STPD conditions. The STPD
correction factor can be calculated using the following equation (TA stands for the
ambient temperature, PA stands for the ambient pressure, and PH2O stands for the water
vapor pressure):
STPD cf =
(273°)
(273 + TA°C)
Lab I - 7
x
(PA mmHg - PH2O mmHg)
(760 mmHg)
6. Calculate VEstpd. The next step is to calculate oxygen consumption. Whenever we
analyze a gas sample for the amount of a particular gas present the volume must be
converted to STPD conditions. Thus, in order to calculate oxygen consumption and
carbon dioxide production you must first calculate VEstpd by multiplying VEatps times
the STPD correction factor.
VEstpd = VEatps x STPD C. F.
7. Calculate Tidal volume. As you learned in your human physiology courses, VE is the
product of tidal volume (TV) and respiratory rate (RR). TV is the volume of air moved
per breath and RR is how many breaths per minute the subject is taking. A typical
resting TV is 0.5L/breath and a typical resting RR is 12-20 breaths/min. Maximal
values.
TVbtps= VEbtps / RR
8. Calculate Alveolar Ventilation. As you learned in your human physiology courses, not
all of the air that is moved in and out of the lungs every minute (VE) actually gets to
the alveoli where gas exchange occurs. This is because there is some amount of dead
space (DS); areas in the lungs that do not participate in gas exchange. For example,
during ventilation some of the air will remain in the respiratory conducting tubes
(trachea, bronchi, and all of the generations of bronchioles); this air will not participate
in gas exchange. The dead space associated with respiratory conducting tubes is
called the anatomical dead space. A healthy young adult usually has a dead space of
about 150 ml or 0.15L. Dead space tends to increase as we age.
In some instances, some of the gas exchange areas (alveoli) are not functional or
are only partially functional because of absent or poor blood flow through the adjacent
pulmonary capillaries. From a functional standpoint, unused alveoli must be
considered dead space. Physiological dead space is the term used when the alveolar
dead space is included in the total measurement of dead space.
When calculating alveolar ventilation then, we must subtract the dead space from
each tidal breath and then multiply times respiratory rate. We will use a constant of
0.15L for dead space.
VAbtps= (TVbtps – DS) x RR
9. Calculating oxygen consumption (VO2). Simply stated oxygen consumption equals
the amount of oxygen inspired minus oxygen expired.
VO2 = O2 inspired – O2 expired
The amount of oxygen inspired can be calculated by multiplying the % of inspired air
that is oxygen (FIO2, which is a constant, 0.2093) times the volume of air inspired
(VIstpd). Similarly, the amount of oxygen expired can be calculated by multiplying the
% of expired air that is oxygen (FEO2) times the volume of air expired (VEstpd). Thus
we can calculate VO2 as follows:
VO2 = (VIstpd x FIO2) - (VEstpd x FEO2)
or
VO2 = (VIstpd x .2093) - (VEstpd x FEO2)
Lab I - 8
a. Calculate the Nitrogen Factor. All variables except VI are known or measured. One
would expect VI to be nearly equal to VE, however it is possible that the two can be
slightly different due to differences in the rate of O2 consumption and CO2 production.
Thus, we need a way to calculate VI that takes this into account. By calculating the
fractional concentration of nitrogen (an inert gas) in inspired gas and expired gas we
can calculate what is called the nitrogen factor (N. F.), which will allow us to
determine VI from our VE value. The nitrogen factor can be calculated as follows:
FEN2
N. F. =
1 - (FEO2 + FECO2)
=
FIN2
1 - (FEO2 + FECO2)
=
1 - (FIO2 + FICO2)
0.7904
b. Calculate VIstpd. The N.F. factor takes into account the difference between VE and VI
such that:
VIstpd = VEstpd x N. F.
Because VE and VI are usually nearly equal, the nitrogen factor is typically very close
to 1.0.
c. Inserting these formulas and the constant 0.2093 for FIO2 to the oxygen consumption
equations we now have the following formula.
VO2 = (VEstpd x .2093 x N. F.) - (VEstpd x FEO2)
or
VO2 = VEstpd(NF x .2093 - FEO2)
As you can see, our ability to take up and utilize oxygen (VO2) is partly dependent
upon our ability to move air in and out of the lungs (VE) and our ability to extract
oxygen from that air (0.2093-FEO2). Remember, the nitrogen factor should be very
close to 1.0.
10. Calculate Relative Oxygen Consumption. These (above) formulas give the oxygen
consumption values in liters per minute. When VO2 is reported in L/min, the value is
considered an absolute value (absolute VO2). A larger individual would be expected
to consume more liters of oxygen every minute, but should consume a certain amount
of oxygen relative to their body size. Oxygen consumption is also frequently reported
relative to body mass in milliliters per kilogram per minute, this is called the relative
oxygen consumption (relative VO2). At rest, relative VO2 is usually around 3.5
ml/kg.min.
VO2 (L/min) x 1000 ml/L
Relative VO2 =
Kg (body mass)
11. Carbon dioxide production (VCO2stpd). To calculate carbon dioxide production you
will use a formula similar to that of the oxygen consumption formula, except that in
this case you will be calculating CO2 expired minus CO2 inspired. Remember, FICO2
is typically constant around 0.0003 (the air we breathe in is 0.03% CO2).
VCO2stpd = (FECO2 x VEstpd) - (VEstpd x NF x FICO2)
Lab I - 9
12. The respiratory quotient (RQ) (which should be called the respiratory exchange ratio,
RER when determined from respiratory measurements at the level of the mouth/nose)
is another valuable measurement that can be determined from our gas sample data. It
is a ratio of CO2 produced to O2 consumed and therefore reflects the type of fuel
substrates being used inside the cells. It is calculated as follows:
VCO2
RER =
FECO2
or it can be estimated by =
VO2
(0.2093 - FEO2)
Appendix page 54 shows how RQ relates to the use of different fuel sources and how
the RQ can be used to give caloric equivalents for oxygen consumption. For example
an RQ of 0.7 indicates that the subject is using fats as their primary fuel source and an
RQ of 1.0 indicates the subject is using carbohydrates as their primary fuel source. An
average resting RQ for most subjects on a normal diet is about .82. Typically the RER
that is calculated from whole body VO2 and VCO2 is called a non-protein RER. To
determine the amount of protein metabolism urinary nitrogen excretion must also be
measured.
RQ is the ratio of CO2 produced to O2 consumed at the cellular level, and it can
never exceed a value of 1. The RER is the ratio of CO2 produced to O2 consumed at
the whole body level, and thus is an estimate of RQ. Under most normal conditions
RER and RQ are almost exactly equal. However, because the RER is measured on the
organism level it represents both metabolism and CO2 produced as a result of
buffering the blood. Any disturbance in the organism’s acid-base balance such during
hyperventilation, metabolic acidosis, respiratory alkilosis and during intense exercise
can cause RER to exceed 1.0. During these situations (or other situations that throw
off acid-base balance) RER and RQ are not equal.
13. Several other calculations will be used today and throughout the rest of the quarter.
a. Ventilation equivalent ratio for oxygen (VE/VO2)
VEstpd
VERO2 =
VO2stpd (L/min)
b. Ventilation equivalent ratio for carbon dioxide (VE/VCO2)
VEstpd
VERCO2 =
VCO2stpd
The ventilatory equivalent ratios can be used to help determine the ventilatory
threshold and can also be used to indicate respiratory efficiency. For example, if a
subject has good gas exchange, they will extract oxygen well and will not need to
ventilate as much for a given oxygen consumption. Thus, they would have a lower
ventilatory equivalent ratio for oxygen than a person with poor respiratory efficiency
(poor gas exchange). When a subject first gets hooked up to the mouthpiece they
usually hyperventilate for a while (VE is higher than it needs to be for that level of
oxygen consumption). As a result, when they are first hooked up, VE/VO2 is
frequently somewhat high and after a little bit it starts to decrease. When the subject
starts to exercise they begin to extract oxygen better (FEO2 decreases) and so they do
not need to ventilate as much for a given oxygen. This also tends to decrease the
Lab I - 10
VE/VO2. Eventually, during high intensity exercise, when the blood needs to be
buffered by respiratory buffering mechanisms, VE starts to go up at a higher rate (this
is at the ventilatory threshold), and thus VE/VO2 also begins to increase. However,
because VCO2 also starts to go up at this time, the VE/VCO2 remains the same.
c. Fick equation for oxygen consumption
VO2 = Q x a-vO2difference
Where Q is the cardiac output and a-vO2 difference is the arterial-mixed venous
oxygen difference. Remember from human physiology, cardiac output equals heart
rate times stroke volume (Q = HR x SV). a-vO2 difference is the difference in the
oxygen content between the arterial and the venous blood and represents the amount of
oxygen taken up from the blood (and utilized) by the tissues. At rest the muscles are
not extracting too much oxygen from the blood so a-vO2 difference is low. But,
during exercise the muscles take up more oxygen and are receiving a greater portion of
the body's blood flow, resulting in a greater a-vO2 difference. See the
cardiopulmonary function lab and/or your textbook for a more complete explanation of
a-vO2 difference.
d. Oxygen pulse
Absolute VO2 (L/min) x 1000ml/L
O2 pulse =
Heart rate (beats/minute)
The O2 pulse is sometimes used to assess trends in stroke volume and is thought to
represent, to an extent, cardiovascular efficiency. For example, if a person has a large
heart they will tend to have a large stroke volume and their heart will not need to beat
as fast for a given oxygen consumption. Thus, they would tend to have a higher
O2pulse. According to the Fick equation from above, what other physiological
variable would be expected to influence the O2pulse (besides VO2, HR, and SV)?
K. After collecting a resting bag and performing the above calculations, collect and analyze
bags taken during two submaximal bouts of exercise using the same subject. Then repeat
these calculations with the exercise data. The exercise bouts will be 5 minute steady state
exercise bouts performed on one ergometer (of your choice) at two different intensities
(the first intensity should be a low-moderate intensity and the second should be a
moderate-high intensity). During each exercise bout a one minute sample of expired air
will be collected during the final minute of exercise. Recommended intensities:
Ergometer
Cycle
Bout I (low-med)
50-75 RPM, 1-2kg
Bout II (mod-high)
50-75 RPM, 2-3kg
Treadmill
fast walk
(3-4mph, low% grade)
moderate jog/run pace
(pace for ~30 min workout)
Rowing Ergometer
50-100 Watts
100-180 Watts
Arm Crank
50 RPM, 0.5-1kg
50-60 RPM, 1-2kg
Lab I - 11
Some expected Normal Values
Correction factors:
Nitrogen factor
STPD c.f.
BTPS c.f.
usually very close to 1.0
usually .85 to .95
usually 1.08-1.12
Rest
VE
4 -15 L/min
Absolute VO2 (men)
0.2 - 0.5 L/min
(women)
0.15 - 0.4 L/min
Relative VO2 (men)
3.5 ml/kg.min
(women)
3.5 ml/kg.min
VO2max for average college age: Male:
Female:
RER
0.7 to 1.0
FEO2
0.15 to 0.18
FECO2
0.025 to 0.06
Lab I - 12
Maximal Exercise
130-250 L/min
2.0 - 7.0 L/min
1.5 - 5.0 L/min
35 - 90 ml/kg.min
25 - 75 ml/kg.min
45 ml/kg.min
35 ml/kg.min
1.0 to 1.5
same as rest range
same as rest range
Data Sheets
I. Metabolic Cart Demo and Calculation of O2 deficit and EPOC.
A. Draw a schematic diagram of the subject, respiratory mouthpiece, tubing and the
components of the metabolic cart including mixing chamber, gas analyzers, air flow
meter, tubes, and connections to the computer. Identify what parts of the
VO2formulas are determined by each part of the metabolic cart.
B. EPOC and O2 deficit data and calculation
Rest
Time
1
2
3
4
5
6
7
8
9
10
VO2
VE
HR
Average resting VO2: ____________
Exercise
Time
Ergometer
1
2
Power
3
4
5
6
Watts
7
8
9
10
VO2
VE
HR
Average steady state VO2: _________
Recovery
Time
1
2
3
4
5
6
VO2
VE
HR
Lab I - 13
7
8
9
10
Calculation of oxygen deficit:
1. Calculate the average steady state oxygen consumption: _____________
2. Calculate the deficit for each minute of exercise before steady state was attained and
sum these deficit values. ________________
Calculation of EPOC:
1. Calculate the average resting oxygen consumption: _______________
2. Calculate the excess oxygen consumption for each minute of recover and sum these
values. ______________________
How do your O2 deficit and EPOC compare? If not the same, which is larger?
How does the body maintain cellular energy homeostasis before aerobic metabolic systems
are “up to speed”?
What are a few reasons why we no longer call EPOC O2 debt?
What do you suppose would happen to the size of the O2 deficit if the subject performed a
higher intensity bout of exercise? How about EPOC?
What do you suppose would happen to the size of the O2 deficit if the subject was more
fit/better trained? How about EPOC?
Lab I - 14
II. Rest and exercise VO2 Calculations
rest
a.
Subject Wt.
b.
Intensity/ergometer settings
c.
Ambient Pressure
d.
Ambient Temperature
e.
Water Vapor Pressure (pH2O)
f.
Heart Rate
g.
FEO2
h.
FECO2
i.
Sample Volume
j.
Meter Volume
k.
ATPS Volume
(= i + j)
l. VEATPS in L/min
(= k / 5 for rest, for exercise = i + j)
m. BTPS corr. factor
n.
o.
p.
VE BTPS in L/min
(= l x m)
STPD corr. factor
q.
VE STPD
(= l x o)
NF
r.
VO2 STPD L/min
s.
VO2 STPD ml/Kg/min
t.
RER
u.
VCO2 STPD in L/min
v.
VE/VO2
w. VE/VCO2
x.
O2pulse (mlO2/beat)
y.
RR (breaths/min)
z.
TV BTPS (L/breath)
aa. VA BTPS (L/min
Lab I - 15
exercise 1
exercise 2
Regarding your resting and exercise calculations:
1) Were your subject’s rest and exercise absolute and relative VO2 values approximately the
right values or in the right range? How about their VE, RER, FEO2, and FECO2 values?
2) What were your subject’s RER values? Did they suggest more fat or carbohydrate use?
What happened to RER with increasing exercise intensity? What do these changes suggest?
3) What happened to FEO2 and FECO2 as your subject went from rest to exercise and then
increased the intensity? What do these changes suggest?
4) What happened to tidal volume and respiratory rate as the subject went from rest to low
intensity exercise? How about from low intensity exercise to moderate intensity exercise?
5) If your respiratory control centers needed to increase VE, would it be better to increase TV or
RR to accomplish the increase in VE? (hint: think about VA)
6) What happened to VE/VO2 and VE/VCO2 as your subject went from rest to exercise and then
increased the intensity? What do these changes suggest? How are these changes related to
changes in to FEO2 and FECO2?
7) What are similarities and differences between RER and RQ?
8) What happened to O2 pulse as your subject went from rest to exercise and as exercise
intensity increased? What do these changes suggest?
Lab I - 16
Lab I study questions
1) Why do we use the STPD correction factor? What variables are reported in STPD
conditions?
2) Why do we use the nitrogen factor?
3) What is the advantage of reporting O2 consumption in ml/kg.min rather than L/min?
6) What happens to FEO2 and FECO2 at the beginning, during the middle, and at the end of a
progressive intensity exercise test? Explain why?
7) What pieces of equipment are needed to make up a metabolic cart? What are the roles of
each of these parts?
8) How are VE, FEO2, NF, FIO2, cardiac output, a-vO2difference, and VO2 all related? Write
out their relationships to each other using formulas (equations).
9) What is Oxygen Deficit and why does it occur?
10) What is EPOC and why does it occur?
11) What are some of the processes occurring early during recovery from exercise? How about
later in the recovery? (see description of fast and slow components of O2 debt)
Lab I - 17
12) What is the formula for the phosphocreatine system? How does this relate to O2 deficit and
EPOC?
13) Given the following data, calculate O2 deficit and EPOC.
Exercise
Ergometer Cycle
Power output 200 Watts Resting VO2 0.25 L/min
Time
1
2
3
4
5
6
7
8
9
VO2
1.25
1.79
2.36
2.58
2.60
2.53
2.57
2.59
2.61
2.57
VE
25
42
57
63
68
71
74
71
69
72
HR
116
10
134
146
153
155
154
156
154
157
155
2
3
4
5
6
7
8
9
10
Recovery
Time
1
VO2
2.01
1.65
1.25
0.71
0.58
0.36
0.29
0.24
0.25
0.25
VE
63
52
41
35
24
18
15
12
10
9
132
122
114
109
96
91
84
81
HR
151
143
O2 deficit:
EPOC:
Lab I - 18
14) Calculate a) absolute VO2, b) relative VO2, c) VCO2, d) VE (in the proper gas conditions),
e) the ventilatory equivalent ratios for O2 and CO2, f) RER, g) O2pulse, h) Tidal Volume,
and i) Alveolar ventilation. Also, j) if their stroke volume was 0.100 L/beat, what would
their a-vO2 difference be?
Subject weight = 135 lb female
Subject = 22 yrs old
Ambient pressure = 751 mmHg
Ambient Temperature = 21C
RR = 22 breaths/min
VE-ATPS = 65.5 L/min
FEO2 = 16.8 %
FECO2 = 3.72 %
HR = 155 b/min
Lab I - 19