Lab I - 1

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

Lab I - 2

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.

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

VO2

(L/min)

Figure 1. O2 Deficit & EPOC

0

0.3

0.6

0.9

1.2

1.5

1.8

-4 -2 0 2 4 6 8 10 12 14 16 18 20

Time (min)

O2 demand

rest VO2

O2

deficit

EPOC

Lab I - 3

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 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

ADP & PCr ATP + Cr Creatine Kinase

Lab I - 4

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

Lab I - 5

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 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.

Lab I - 6

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

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.

Lab I - 7

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)

Lab I - 8

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 (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°) x (PA mmHg - PH2O mmHg)

(273 + TA°C) (760 mmHg)

Lab I - 9

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:

Lab I - 10

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

Lab I - 11

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)

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 FECO2

RER = 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 =

Lab I - 12

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-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

Lab I - 13

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, 2-3kg

Treadmill fast walk moderate jog/run pace

(3-4mph, low% grade) (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

Some expected Normal Values

Correction factors:

Nitrogen factor usually 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/min 2.0 - 7.0 L/min

(women) 0.15 - 0.4 L/min 1.5 - 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

Lab I - 14

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 Ergometer Power Watts

Time 1 2 3 4 5 6 7 8 9 10

VO2

VE

HR

Average steady state VO2: _________

Recovery

Time 1 2 3 4 5 6 7 8 9 10

VO2

VE

HR

Lab I - 15

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 - 16

II. Rest and exercise VO2 Calculations

rest exercise 1 exercise 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

Lab I - 17

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 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?

Lab I - 18

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 - 19

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 - 20

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 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 1 2 3 4 5 6 7 8 9 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:

Lab I - 21

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 VE-ATPS = 65.5 L/min

Subject = 22 yrs old FEO2 = 16.8 %

Ambient pressure = 751 mmHg FECO2 = 3.72 %

Ambient Temperature = 21C HR = 155 b/min

RR = 22 breaths/min