Oxygen Consumption
Lab IOXYGEN 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 bodys 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 todays 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.
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 bodys 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.
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 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 cells 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 cells 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 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.
LABORATORY PROCEDURESI. 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
Calculationsa. 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 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. 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( PA - PH2O 273( + TA 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 (0C)
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) x (PA mmHg - PH2O mmHg)
(273 + TAC) (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 / RR8. 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 RR9. 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) 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 1 - (FEO2 + FECO2) 1 - (FEO2 + FECO2)
N. F. = = =
FIN2 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/LRelative 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)
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
FECO2RER =
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 organisms
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 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-vO2differenceWhere 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/LO2 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
Bout I(low-med)
Bout II (mod-high)Cycle
50-75 RPM, 1-2kg
50-75 RPM, 2-3kgTreadmill
fast walk
moderate jog/run pace
(3-4mph, low% grade)(pace for ~30 min workout)
Rowing Ergometer50-100 Watts
100-180 Watts
Arm Crank
50 RPM, 0.5-1kg
50-60 RPM, 1-2kg
Some expected Normal Values
Correction factors:
Nitrogen factorusually very close to 1.0
STPD c.f.
usually .85 to .95
BTPS c.f.
usually 1.08-1.12
Rest
Maximal Exercise
VE
4 -15 L/min
130-250 L/min
Absolute VO2 (men)
0.2 - 0.5 L/min2.0 - 7.0 L/min
(women)0.15 - 0.4 L/min1.5 - 5.0 L/min
Relative VO2 (men)
3.5 ml/kg.min
35 - 90 ml/kg.min
(women)3.5 ml/kg.min
25 - 75 ml/kg.min
VO2max for average college age:Male:
45 ml/kg.min
Female:35 ml/kg.min
RER
0.7 to 1.0
1.0 to 1.5
FEO2
0.15 to 0.18
same as rest range
FECO2
0.025 to 0.06
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
123456789 10
VO2
VE
HR
Average resting VO2: ____________
Exercise
Ergometer Power Watts
Time
12345678910
VO2
VE
HR
Average steady state VO2: _________
Recovery
Time
12345678910
VO2
VE
HR
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?
II. Rest and exercise VO2 Calculations
restexercise 1exercise 2
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.VE BTPS in L/min
(= l x m)
o.STPD corr. factor
p.VE STPD
(= l x o)
q.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
Regarding your resting and exercise calculations:
1) Were your subjects 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
subjects 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 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)
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
123456789 10
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 116 134 146 153 155 154 156 154 157 155
Recovery
Time
123456789 10
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
HR 151 143 132 122 114 109 96 91 84 81
O2 deficit:
EPOC:
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 femaleVE-ATPS = 65.5 L/min
Subject = 22 yrs old
FEO2 = 16.8 %
Ambient pressure = 751 mmHgFECO2 = 3.72 %
Ambient Temperature = 21(C
HR = 155 b/minRR = 22 breaths/minCreatine Kinase
EPOC
O2 deficit
rest VO2
O2 demand
Time (min)
20
18
16
14
12
10
8
6
4
2
0
-2
-4
1.8
1.5
1.2
0.9
0.6
0.3
0
Figure 1. O2 Deficit & EPOC
VO2
(L/min)
ATP + Cr
ADP & PCr
PAGE Lab I - 17
