The purpose of this experiment is to measure oxygen consumption and ventilation at rest and during incremental exercise.

Nicholas Wright

Physiology Laboratory – Analysis of Expired Air

Content

The stress that is imposed on the human body by strenuous physical effort varies with the level of the maximal capacity of the body to perform exercise. If an individual has a physical working capacity of a certain amount and does exercise at a level of 50 per cent of his capacity, he is under much less stress than another person doing the same activity using 70 per cent of his capacity. The larger the level of the physical working capacity of an individual, the more strenuous exercise he will be able to take and the less stress he will have imposed on him by any particular exercise level relative to someone of a lower exercise capacity.

The most useful measurement is that of the maximal oxygen uptake (VO2 max) by the body, because this indicates the maximal capabilities of the respiratory and cardiovascular systems to supply oxygen (and therefore release energy) to the working muscles. As an example, two men of the same body size may have a VO2: max 3 l/min in the one case and 2 I/min in the other. If they each have to do work that requires an oxygen consumption 1.5 l/min (approx. 7-8 kcal/min (29-33 KJ)), this work level is 50 per cent of the maximal capability of the first man but 75 per cent that of the second. (Astrand, P.O.1956)

Vo2 max is often expressed, not as l/min but as ml/kg of body mass/mint Very approximate levels for people of varying degrees of fitness might be 3545 ml/kg/min for an average young man and 50 ml or more for a young man of higher levels of fitness. Extremely fit men may have values of 70-80 ml/kg/min or even higher, but these are exceptional values. There is also a difference between the sexes, with women having about 15-20 per cent lower values. Mc Ardle, Katch, Katch (1994).

When O2 max is being measured on an individual, it can be measured either directly by having the person do exercise up to the extremes of his or her capability, or else by sub-maximal tests where the results are extrapolated to supposedly maximal values. Both approaches have their drawbacks. The direct measurement, to be a valid reflection of the real maximal working capacity of the individual, requires considerable motivation: it is a somewhat unpleasant experience for those not accustomed to it to exercise to complete exhaustion. Unless repeated measurements are made on each individual, it is unlikely that a real VO2 max will have been obtained.

The drawback to the sub-maximal approach concerns the accuracy of the extrapolation. As the exercise is sub maximal, motivation becomes less relevant. The extrapolation requires heart-rate to be measured (sometimes in conjunction with oxygen uptake) during three or four different levels of standardized exercise, up to a moderately strenuous degree.

However, two sources of error arise. First, sub maximal heart-rates can vary within the individual independently of the exercise, because of such influences as emotion, time of day, effects of eating or drinking, smoking, temperature, etc. And second, a direct extrapolation from sub-maximal heart-rates to maximal will not represent the normal situation, because at near maximal values the relationship of heart-rate to oxygen uptake is different from that at lower levels of exercise. However, the error is seldom large, and a sub-maximal test, especially in a nutritional context, is the method of choice. With experience and especially under laboratory conditions, ...

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Introduction

The purpose of this experiment is to measure oxygen consumption and ventilation at rest and during incremental exercise. The main focus being, the effect incremental exercise has on minute ventilation (VE), which is the volume of air exhaled in a minute, the volume of oxygen consumed per-minute (VO2), and carbon dioxide production per-minute (VCO2). Ventilatory equivalent for oxygen is a measure of air breathed per litre of oxygen consumed per minute, and this will also be considered.

Ambient air has a Standard atmospheric pressure (at sea level) = 760 mmHg.

It also has a composition made up of approximately;

1) 79.0% Nitrogen (N2) (the partial pressure of nitrogen (PN2) = 600.7 mmHg),

2) 20.93 Oxygen (O2) (PO2 = 159.1 mmHg)

3) 0.03% Carbon dioxide (CO2) i(PCO2 = 0.2 mmHg)

(www.faculty.de.gcsu.edu/~mmartino/Chapter08.ppt)

During exercise it would be expected that expired oxygen concentration would decrease by around 16%, while carbon dioxide can increase by as much as 4%, nitrogen being metabolically inert would remain unchanged. .( Consolazio, Johnson , Pecora (1963))

In a practical situation this information is useful for elite athletes looking to increase the intensity at which lactate production increase, i.e. shifting the ventilatory breakpoint right.( Consolazio, Johnson Pecora. (1963)) This information is also useful for subjects concerned with increasing the duration of the line, i.e. showing they can continue to work at higher power output levels for longer. (Wasserman , Hansen, Sue , Whipp , Casaburi , (1994))

This method should give a good objective measure of any training adaptations, which can include improvements in gas exchange at the lung and in muscle with sustained training, detailed descriptions of physiological improvements due to training can be found in a study by Wilmore , Costill (1973).

Method

One recreationally active student volunteered to participate in the experiment. The maximal test was undertaken using a Monarch Excalibur cycle ergo meter, with incremental power output applied after every four minutes.

During the experiment, there were several different types of equipment that was used to gain results, a Douglas bag, two way stopcock, breathing value, mouthpiece, nose clip, dry gas meter, gas analysers, stopwatch, barometric scale and a cycle ergo meter.

The subject was started on 100 Watts and was allowed to adapt to the intensity for three minutes. On the three minute mark the subject was connected to a Douglas bag via a mouthpiece and tubes with a nose clip applied. The subject then breathed into the bag for approximately one minute, the breaths were counted from the end of expiration and collected for a whole number of breaths, explaining why the duration of the sample exceeded one minute, and this was timed using a stopwatch. After the sample was collected the breathing valve was shut sealing the bag. Heart rate and rate of perceived exertion, RPE (where 6 being very, very easy and 20 being very, very hard) readings were taken before the increase in intensity and start of the next four minute period.

The sealed Douglas bag was shaken to mix up the air collected and then connected to a gas meter. The gas meter gave readings for concentration of oxygen and carbon dioxide from the sample. The time taken for these readings to be determined was timed and the flow rate noted. This allows the loss of gas to be added onto the volume of gas in the bag, which was recorded next. The Douglas bag, now emptied was replaced ready to be reused to collect air. The subject then continued cycling, increasing the power output each time until eventually fatigue got the better.

Room temperature and barometric pressure were observed which allowed VE to be converted into STPD (Standard Temperature and Pressure dry). This takes into account environmental weather changes concerning temperature and pressure allowing accurate comparison between the experiments on two different days.

When the subject finally stopped, FEO2, FECO2 and the volume of expired air (litres) was measured using the dry gas meter.

After all the results were collected from the experiment, these were tabulated allowing comparison of VO2 (∫.min-1), VCO2 (∫.min-1), VE (∫.min-1),

Results

Figure One

Figure 2

Figure 3

Figure 4

Figure 5

Discussion

As exercise intensity increases toward the maximum, ventilation increases slightly, when compared with oxygen consumption. This is called Ventilatory breakpoint, and is demonstrated in graph 1. The first three to four points show the subject to be working at a steady state, ‘where heart rate is maintained constant at sub-maximal levels of exercise when held’ (Wilmore and Costill, 1999). At a steady state ventilation will increase proportionally with rate of energy metabolised, i.e. the body matches aerobic metabolism to the energy requirements (McArdel et al 1996). Oxygen yields a fixed amount of energy, 1 litre of oxygen holds about 20 000 Joules. 1 Watts is equivalent to 1 J/Sec. Therefore at 100 Watts power output 100 J/Sec is required. At the fifth and sixth point the ventilatory breakpoint has been exceeded and ventilation can be seen to be increasing disproportionately compared to oxygen consumption. This occurred in the later stages of the experiment as the subject approached their maximum work rate. The ventilatory breakpoint will typically occur at 55-70% of VO2 MAX. (Wilmore and Costill, 1999). )

In order for oxidation to carry on, more energy is needed from glycolsis. Glycolsis is increased and in turn, so is the lactic acid that is produced and this increases slowly. The lactic acid combines with the sodium carbonate, which forms sodium lactate, water and carbon dioxide. Carbon dioxide stimulates chemo receptors that increase ventilation in the respiratory centre. (Wilmore 1994)

The term lactate threshold refers to the highest exercise level (intensity) or level of oxygen uptake that is not associated with an elevation in blood lactate concentration above the pre exercise level. (McArdle 1996)

The Ventilatory break point reflects the respiratory response to increased carbon dioxide levels. (Wilmore 1994)

Past the ventilatory breakpoint oxygen delivered to muscles can no longer meet the body’s requirements causing the body to produce more energy through glycolsis which results in greater lactic acid production and accumulation. (Wilmore and Costill, 1999). This may have been what prevented the subject from reaching maximal heart rate as the build up of lactic acid in the muscles prevented the subject from continuing until a high enough intensity to bring the onset of maximal heart rate. Graph 4 shows a linear increase in heart rate as the rate of work goes up and I have predicted using the regression analysis and the line of best fit, that if the work intensity stayed the same the subject would reach maximal heart rate at or around the 400 watt stage.

When lactic acid accumulates pH starts to fall, this is known as acidosis, and the body tries to maintain pH at around pH 7.1 – 7.4. To do this the body utilises chemical base substances stored in blood and muscle which combine with lactate and buffer / neutralise them Wilmore JH, Costill DL (1973)

When lactate combines with sodium bicarbonate, which acts as the buffer sodium lactate, water and carbon dioxide are formed. The base then carries the O2 and water molecules to the lungs to be exhaled and then return to working muscle to be reused. The increase in CO2 stimulates chemo receptors which signal for an increase in ventilation to blow off CO2. This is demonstrated in graph 3, showing the large increase in carbon dioxide occurring at the same point as the ventilatory breakpoint.

The result of this sustained activity by the chemo receptors increasing ventilation is also demonstrated in graph 5, where the volume of air in the bag increases at a steady pace until just after the breakpoint which gives way to a more rapid uptake of air.

An increase in VCO2 at 225 watts is due to the accumulation of lactic acid in the muscles and so more CO2 is produced to remove the lactic acid. The two graphs, that were produced VE and VCO2, show similarity. The ventilatory break point is also at the same point (225 watts). Ventilation is driven by the need to get rid of carbon dioxide.

On a more applied and practical note, V O2 Improves with training, An effective training program can both increase VO2 max and improve endurance at a specific level of VO2. While improvements are gradual, periodic re-evaluation of VO2 intensity detects changes in aerobic fitness and helps plan appropriate advancements (http://www.preventionsolutions.com/Exercise%20Testing.htm)

References

Consolazio C, Johnson R, Pecora L. (1963). Physiological Measurements of Metabolic Functions in Man. New York NY: McGraw Hill

Mc Ardle WD, Katch FI Katch VL (1994). Essentials of Exercise Physiology. Malvern PA: Lea & Febiger

Wasserman K, Hansen JE, Sue DY, Whipp BJ, Casaburi R, (1994). Principles of Exercise Testing and Interpretation. 2nd Ed. Malvern PA: Lea & Febiger

Wilmore JH, Costill DL (1973). Adequacy of the Haldane transformation in the computation of exercise VO2 in man. Journal of Applied Physiology, 35, 85-89

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http://www.preventionsolutions.com/Exercise%20Testing.htm

Exercise Physiology Fouth edition – William D. Mcardle, Frank I.Katch, Victor L.Katch

Physiology of Sport and Exercise. Jack H Wilmore, David L. Costill

Astrand, P.O., "Human Physical Fitness with Special Reference to Sex and Age," Physiol Rev., 36: 307-335 (1956).

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