LABORATORY HANDBOOK ERGOMETRY. For the course. Human Physiology

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1 LABORATORY HANDBOOK ERGOMETRY For the course Human Physiology Karolinska Institutet Department of Physiology and Pharmacology Physiology Education Postal address: Stockholm Visiting address: Nobels väg 9 Tel exp: Tel vx:

2 ERGOMETRY LABORATORY: EXERCISE, LACTATE THRESHOLD AND MAXIMAL OXYGEN UPTAKE Introduction The purpose of the following laboratory exercise is to give you practical knowledge in how to perform a maximal oxygen uptake test and how to measure and assess maximal oxygen uptake. Following the lab you are expected to know: How heart rate and oxygen uptake vary with increased workload during exercise. How a submaximal (indirect) test can be used to estimate a person s maximal oxygen uptake. How a maximal oxygen uptake test (direct) is administered and which parameters are necessary to measure the oxygen uptake. Changes in lactate that occur during exercise. This laboratory exercise consists of: 1. A submaximal test to estimate maximal oxygen uptake. Blood lactate samples will be taken during this test. 2. A maximal test to measure maximal oxygen uptake. Human Physiology Ergometry rev Fall16 2

3 In order to measure maximal oxygen uptake (VO2 max), one must analyse the difference in oxygen content between inspired and expired air. The classic method is to collect the expired air in a Douglas bag (a gastight sack) and then measure the volume of the expired air and also analyse the content of oxygen (O2) and carbon dioxide (CO2) in it. Since the collection time and the composition of inspired air is known (20.93 O2 and 0.03 CO2), one can calculate the ventilation (VE), VO2, and VCO2. An alternative method is to sample online, where the expired air flows through a device which automatically measures and records the volume and the O2 and CO2 content. These two methods use advanced equipment, several administrators and the subject must undertake a maximal workload. oxygen upt ake maximal oxygen upt ake wor kload Figure 1. Figure shows the relationship between workload and oxygen uptake. In order to measure maximal oxygen uptake, the workload must be increased stepwise to a level where oxygen uptake does not increase further even if the workload is increased. An easier way is to make an indirect measurement of the maximal oxygen uptake, the socalled Åstrand test. The advantages of this test are that it is simple, does not need complicated equipment and the test subject avoids having to do a full maximal workload test which is physically demanding and can, in some cases, be dangerous. The Åstrand test consists of a submaximal workload on a bicycle ergometer and the pulse that the subject has at the end of the test is used to estimate the maximal oxygen uptake. In order to have a fuller understanding of this, a short background is given below before the actual laboratory is described. The cycle ergometer When one pedals one full revolution on a cycle ergometer, one moves a point on the flywheel 6 metres. A belt presses against the flywheel and exerts friction which brakes the wheel. The amount of braking can be adjusted by changing turning the blue handle. If the pedalling speed is 50 revolutions per minute, this means that the distance covered is 6 x 50 which is 300 metres per minute. If the braking is 1 kg (corresponding to a 10 N load or 1 kp on the ergometer), then the work is 300 x 10 which is 3000 Nm. Kp is a measurement of how much friction the belt exerts on the flywheel. The workload or work intensity corresponds to the work done in a given time and is defined as power expressed in Nm/s or watts (W). If work of 3000 N is done in 1 minute, this means that the workload is 3000/60 or 50 Nm/s or 50 W. Human Physiology Ergometry rev Fall16 3

4 Heart rate and oxygen uptake If the heart rate is measured at the end of a period of sub-maximal work on a cycle ergometer, it can be used to estimate maximal oxygen uptake. However, it is important to note that it takes several minutes before heart rate and oxygen uptake reach a steady state level where the oxygen uptake matches the oxygen need, and the heart pumps enough blood to the working muscle to meet its oxygen demands. In the first few minutes of work, the oxygen uptake does not match the needs of the working tissue. The deficit is met by anaerobic respiration as well as using the oxygen bound to hemoglobin and myoglobin. Figure 2. Heart rate and oxygen uptake during the initial minutes at a given workload. The increase in heart rate has the same time lag as the increase in oxygen uptake. Thus, the heavier the workload is, the higher will be the heart rate until a subject s maximal heart rate is reached. A subject s maximal heart rate is not affected by training although it decreases with age (Taken from Konditionstest på cykel, Anderson et al., 1997). 6 Workload and oxygen uptake According to a study by Åstrand, when steady 5 state has been reached the relationship between 4 workload on the cycle ergometer and oxygen uptake is linear. In other words, the workload 3 can be translated into a known oxygen need. However, there is some variation depending 2 upon an individual s resting oxygen consumption and the mechanical efficiency. 1 Efficiency is expressed as a percentage of the 0 work done to the energy used. For cycling (at rpm), this is about 25% regardless of Work load (W) age, weight or amount of training. VO2 (L/min) Figure 3. Relationship between workload and oxygen consumption. Human Physiology Ergometry rev Fall16 4

5 To summarise the previous two sections, there is a linear relationship between heart rate and workload or oxygen consumption. By measuring during steady state, at different submaximal levels of exercise, one can plot the relationship between the two for an individual. If one knows or establishes the maximal heart rate, one can extrapolate the curve to that point. Alternatively, the maximal heart rate is estimated from the person s age. Thus, the workload that one would have at maximal heart rate can be translated to a known oxygen demand and gives a reasonably good estimate of maximum oxygen uptake. heart rate tr ue max hear t r ate estimated max heart rate wor k l oad estimated max oxygen upt ake true max oxygen uptake oxygen upt ake Figure 4. The relationship between heart rate and workload/oxygen uptake can be used to estimate maximal oxygen uptake. Respiratory quotient (RQ) or the Respiratory exchange ratio (RER) In a healthy individual, muscles rely on carbohydrates and fats for their fuel. The relationship between burning of carbohydrates and fats can calculated from the respiratory quotient (RQ). The RQ is the ratio between the volume of expired CO2 (VCO2) and the volume of inspired O2 (VO2). When only carbohydrates are used, the ratio is 1 and, theoretically, if only fats were used the ratio would 0.7. In someone with a normal mixed diet, these contribute almost equally at rest and during light work and the ratio is about Breakdown of glucose: C6H12O6 + 6 O2 6 CO2 + 6 H2O (Reaction 1) RQ = 6 CO2/6 O2 = 1.0 Breakdown of fatty acid (in this case linoleic acid): C17H35COOH + 26 O2 18 CO H2O (Reaction 2) RQ = 18 CO2/26 O2 = 0.7 Human Physiology Ergometry rev Fall16 5

6 With increasing workloads, the proportion of carbohydrate utilised increases. Up to 1, the RQ describes how carbohydrates and fats are used as energy supplies. With RQ values more than 1, it becomes a measure of how much CO2 is breathed out owing to the increased H + that incurs together with the accumulation of lactate which dives Reaction 3 to the right. H + + HCO3 - H2CO3 H2O + CO2 (Reaction 3) An estimate of the RQ is always included with the measurement of maximum VO2 in order to check if the RQ is greater than 1. One then has an objective measure of whether the work done has been maximal. Cycle ergometer or Åstrand test This test is often used during a health check to determine a person s physical performance. It can be used not only to detect people who have potential health problems but also to encourage individuals to maintain their physical activity. The test is based on the principles described above. The subject cycles at a workload where the heart rate lies in the range of 130 to 160 beats/minute. The reason why one chooses 130 is that then the stoke volume is maximal. The heart rate is measured every minute. The heart rate is used to determine if steady state is reached. Then with the aid of tables and a nonogram one calculates maximum oxygen uptake. The values in the tables and nonogram are based on research carried out on a large number of subjects. In order for the value to be valid, the subject must have a similar maximal heart rate and oxygen uptake as the mean value of the population at a given workload. If one knows the subject s maximal heart rate, then one can correct for this and get a more accurate measure of maximum oxygen uptake. Usually, the initial workload is W for women and W for men but one should take account of age, bodyweight and training status in determining the load. Acid-base changes during physical work Metabolism is said to be acidogenic in that it gives rise to products that tend to reduce the ph of the blood. In a healthy subject, the main task of the acid-base regulatory systems is to eliminate these acid products. The body uses the kidneys, the lungs and the buffer systems to control acid-base balance. As everyone knows, a buffer is a substance that works to stabilise the ph of a solution. The buffer systems are especially important in the early phase of any acid-base disturbance. The following are the main buffer systems in the body and the most important of these is bicarbonate. Bicarbonate Plasma proteins Haemogloblin Phosphate The role of the lungs in acid-base regulation is to eliminate CO2 via alveolar ventilation. This reduces [H + ] because Reaction 3 is driven to the right. The kidneys contribute to excretion of H + by acidifying the urine. In addition, the kidneys exert control of the bicarbonate concentration through reabsorption and in some cases even the production of bicarbonate. Human Physiology Ergometry rev Fall16 6

7 Usually, the ph of the body fluids is maintained within very tight limits. The ph of extracellular fluid ranges between 7.35 and 7.45 (corresponding to 35 to 45 nmol/l [H + ]). These concentrations are extremely low when compared to Na + (142 mmol/l), Cl - (104 mmol/l) or bicarbonate (HCO3 -, 24 mmol/l). In an average day, oxidation of food produces about 13 mol of carbonic acid and normal physical activity about the same amount again.in addition, about 70 mmol of phosphoric acid and sulphuric acid and measurable amounts of organic acids such as lactic acid are also produced. Changes in the acid-base balance are either acidotic or alkalotic in nature. The classification of acid-base disturbances is further characterised by the cause, which can be metabolic or respiratory. All changes in acid-base balance that are not primarily caused by a respiratory disturbance are defined as metabolic, irrespective of the cause. It is important to remember that retention or loss of H + ions does not necessarily bring about a change in ph since the condition may be fully compensated. Figure 5. Acid-base disturbances and the normal situation (N) with respect to ph and [HCO - 3] changes. Respiratory acidosis results from a reduced respiration or reduced alveolar ventilation so that CO2 cannot be excreted. When respiration is disturbed, the ph of the arterial blood can fall from 7.4 to 7.0 in less than five minutes. Respiratory alkalosis is produced by hyperventilation typically in someone who is anxious. Voluntary hyperventilation can result in a ph of 7.7. Metabolic acidosis results from an increased production of H + ions or the loss of alkalis. In this condition, the ph of the blood falls and [HCO3 - ] is reduced. Excess H + ions are buffered by bicarbonate and the protein buffers. As a consequence, [HCO3 - ] is reduced and the extent of the reduction will be determined by how pronounced the metabolic acidosis is. Metabolic alkalosis occurs as the result of vomiting or the ingestion of excessive alkalis for duodenal ulcers. Both ph and [HCO3 - ] are elevated. Human Physiology Ergometry rev Fall16 7

8 Respiratory acidosis is the retention of H + ions primarily due to an elevated pco2. Respiratory alkalosis is the loss of H + ions primarily due to a reduced pco2. Metabolic acidosis is the retention of H + ions characterised by a reduced [HCO3 - ]. Metabolic alkalosis is the loss of H + ions characterised by an elevated [HCO3 - ]. In all of the conditions mentioned above, renal and respiratory compensation are set in motion to try and normalise ph. In metabolic acidosis, the respiratory centre is stimulated to increase ventilation which is followed by a fall in pco2. This is described as compensated metabolic alkalosis. The ph value has been shifted towards normal. The H + ions that brought about the acidosis have not been eliminated but merely balanced by a fall in [HCO3 - ]. The protons must be excreted by the kidneys in a buffered form. During physical work, especially anaerobic work, large quantities of acid metabolites are formed. If the acid-base regulatory mechanisms mentioned above were not working, the blood s ph would fall to a level that was incompatible with life. However, the compensatory mechanisms are not able to fully prevent falls in ph either local or systemic. The principle aim of this laboratory is to show how the body reacts and adjusts to the increased production of acid metabolites that is caused by physical work. It will also show which analyses are required in order to know the status of the body s acid-base balance. Blood samples are analysed before and after physical work. Arterial blood is needed to get a good idea of the acid-base status. Venous blood contains too many factors that are dependent on the tissue from which it comes. However because it is rather tricky to take an arterial blood sample, we will take a sample of capillary blood. The laboratory assistant will help you to take a capillary blood sample from a finger tip in a heparinised capillary tube. The blood sample is then analysed in a blood-gas analyser. There are a number of different types of blood-gas analysers but the ones that are used here analyse ph, pco2, and po2 and calculate a number of other parameters. The important ones in arterial blood are shown below (For those of you used to pressures in mm Hg, remember that 1 kpa = 7.5 mm Hg). ph is the H + ion activity. Normal range: pco 2 is the partial pressure of carbon dioxide. Normal value (mean ± SD): 5.2 ± 0.9 kpa. po 2 is the partial pressure of oxygen. Normal value (mean ± SD): 12.0 ± 2.2 kpa BE is the base excess. This is defined as the amount of strong acid that is required to be added to one litre of blood to adjust the ph to 7.4 with a pco2 of 5.3 kpa. It is basically a measure of the blood s buffering capacity. A positive value indicates a surplus of alkali and a negative number indicates a proton surplus. Normal range in males (larger in females): to St HCO 3 - is the standard bicarbonate. This is the bicarbonate concentration in fully oxygenated blood with a pco2 of 5.3 kpa at 38 ºC. Normal range is mmol/l. Human Physiology Ergometry rev Fall16 8

9 Lactate threshold test This method builds upon the increased lactate production and accumulation that occurs at a certain point during a progressive exercise test. This point, called the lactate threshold, varies from person to person and indicates that there is an equilibrium between lactate production and removal of lactate. Usually it is abbreviated as OBLA 4mM. Thus, if one works at an intensity higher than that at which blood lactate is 4 mm, a rapid accumulation of lactate will occur. The type of change could be an increase in running speed from 4.25 min/km to 4.17 min/km or an increase in workload on a cycle ergometer from 250 W to 275 W. This illustrates the point that only a slight rise in intensity is needed to cause blood lactate to rise. The test is usually carried out by having a subject exercise for four minutes at a workload and to have at least four different workloads. The test is a good predictor of an individual s performance in endurance events and even provides a good basis for recommending an appropriate training speed. To slightly oversimplify, maximum oxygen uptake (VO2 max), which depends on both central and local factors, is a measure of total oxidative capacity while the lactate threshold is a more specific characteristic that measures both aerobic capacity and anaerobic capacity. Lactate (mm) OBLA WORK LOAD Corresponding to OBLA Figure 6 The relationship between intensity of work and lactate concentration in the blood. WORK LOAD Human Physiology Ergometry rev Fall16 9

10 Measuring and calculating oxygen uptake When oxygen uptake (VO2) is measured, the difference in between inhaled and exhaled oxygen volume is analyzed. The classical method is to collect the expired air in Douglas bags and analyze the volume and oxygen content. During continuous, on-line measurements, the expired air flows through a gas analyzer and a flow meter where the volume, oxygen and carbon dioxide content is analyzed and recorded automatically. The equation for calculation of oxygen uptake is: VO 2 O2in O2ut 100 VE STPD VO 2 = Oxygen uptake (L/min) O 2 in = Oxygen content (in %) of inspired air O 2 ut = Oxygen content (in %) of expired air VE STPD = Minute ventilation (L/min) at Standard Temperature Pressure and Dry (the volume at a certain temperature, pressure and dry gas) Procedure The subject should be healthy, have not eaten in the past two hours, have not smoked or used snus in the hour prior to the laboratory, and have not undertaken hard physical exertion that day. The subject should also wear exercise clothing. Divide the following tasks between the remaining the group members: Time-keeper, who will lead the experiment and tell the rest of the group when to take measurements. Person responsible to change the intensity on the ergometer by turning the blue handle. The intensity is checked on the side of the ergometer (see below). Person responsible for recording the heart rate, which will be registered on the display. This person will also make sure that the subject pedals with the correct cadence, which is also registered on the display. One or two people who will measure blood lactate levels. Wear gloves!!! Ask a teacher for instructions about how to use the Accusport. Person responsible for the Borg-scale. The subject will estimate his/ her effort (legs and breathing) by pointing to the scale. Record-keeper who will record the values on the white board during the experiment. Human Physiology Ergometry rev Fall16 10

11 1. The subject undertakes sub-maximal work for 4 minutes at a minimum of 4 different intensities. A blood lactate concentration of more than 4 mm must be achieved. 2. At the end of every intensity as well as after a maximum test, capillary blood from a finger is used to determine blood lactate in the Accusport. The test strip is inserted into the machine and a drop of blood is place on the test strip. The Accusport measures the lactate concentration in one minute. This value is needed to calculate the OBLA 4 mm level 3. At the end of the sub-maximal test, the subject should cool down and rest while the VO2 max is calculated which will determine the workload used in the maximal test. 4. Finally, the subject undertakes a maximal test to measure VO2 max. Heart rate recording Heart rate is recorded using a heart rate monitor. Moisten the chest strap (the transmitter) and attach it around the chest. When there is contact between the display and transmitter a heart will flash on the display and the heart rate can be seen. Oxygen uptake recording The oxygen uptake is continuously recorded during the maximal test by a gas analyzer which records the concentration of O2 and CO2 in the expired air. A flow meter analyzes the volume of expired air. With the help of these variables, it is possible to calculate the amount of consumed oxygen and produced carbon dioxide. Submaximal test Start the test by dividing the different responsibilities among the group. 1. At rest, measure the resting heart rate, the blood lactate and the acid-base status. 2. Adjust the height of the saddle (the knee should be slightly bent when the pedal is in its lowest position). 3. Following a short warm up, the subject will cycle for at least 4 minutes at each workload to achieve steady state. The initial workload should be low, usually 75 W (= 1.5 kp) for women and 100 W (= 2 kp) for men and then it will be increased by 25 W every fourth minute. If the difference in heart rate over the last two minutes is more than 3, then continue for another minute or until the heart rate is steady before increasing the load. Steady state much be reached before the workload is increased. 4. Choose and write down the workload (intensity). 5. Heart rate is continuously recorded with the heart rate monitor. Read it every minute and enter the value in Table A blood sample for lactate measurement is taken during the last 60 seconds of each stage. Note the lactate concentration, work load and effort (from the Borg scale) at the end of each stage. Human Physiology Ergometry rev Fall16 11

12 7. When the blood lactate level is above 4 mm and the subject has cycled at a minimum of four workloads, the test will stop. 8. The subject then winds down on a lower workload and finally rests. During this time, the rest of the group calculates VO2 max. Date: Subject: Age: years old Weight: kg Initial workload: Watt Human Physiology Ergometry rev Fall16 12

13 Workload (W) Rest Sub-max Rest Max. test Table 1 Pulse 1 Pulse 2 Pulse 3 Pulse 4 Lactate (mm) Exertion Human Physiology Ergometry rev Fall16 13

14 2) Draw in the blood lactate concentrations versus the different loads and mark the load at which the subject reached the OBLA 4 mm. Lactate (mm) Workload (W) 3 a) Estimate the subject s VO2 max from the heart rate during steady state at one workload (the workload must be more than 130 beats/minute). Use the attached nonogram. Correct for age according to the attached table Age correction. Estimated VO2 max: l/min After correction for age: l/min Human Physiology Ergometry rev Fall16 14

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16 b) Calculate the subject s VO2 max from the graph below and Figure 3. Use all four workloads and extrapolate the curve to the person s estimated maximum heart rate (220 beats/min age is often used to estimate maximum heart rate). Heart rate (beats/min) Workload (W) Maximal test The initial workload in the maximal test should correspond to about 60% of the subject s estimated VO2 max. Calculate the workload based on the earlier calculation of VO2 max and do not forget that the subject will cycle at 60 revolutions/min, which means that 1 kp is equivalent to 60 W. Assign one person to handle the weights and one who is in charge of the protocol. There should also be a person who notes down the estimated effort, the heart rate and one to keep the time. 1. The file Arbetsprov max will be open and the following screen will be displayed. Do not close the program!!! Human Physiology Ergometry rev Fall16 16

17 Log window; data sparas saved every var 10:e s Graf; Oxygen syreupptag uptake over (l/min) time mot tid (s) Klicka Click +/- på to +/-change för att ändra the scale skalan Comment Add Graf; RER mot tid (s) Graf; hjärtfrekvens mot tid (s) Visar hjärtfrekvensen Start RER over time 2. Put the mask on the subject and adjust the workload. Allow the subject to warm up for 5 min at 100 W and check that the oxygen consumption is around 1.5 l/min (this is a way to calibrate the equipment). To start the recording, press Start in the lower right corner of the screen. 3. Start the test at the workload that you calculated above. Every minute the load is increased by 30 W until maximal oxygen uptake and workload is achieved. It is important that the rest of the group motivates the subject during the test! 4. The exhaled air is continuously being recorded during the test. Oxygen uptake and other parameters can be followed on the screen throughout the test. Record heart rate by looking at the heart rate monitor and Borg scale by letting the subject point to a number on the scale. 5. Immediately after the test is finished the heart rate will be noted. At 3 minutes post exercise, take a sample of blood for the determination of lactate and acid-base content. Note that the subject cannot wind down before the 3 minute post exercise lactate measurement is taken. Write the value in Table 1. Subject s maximal heart rate: beats/min Final workload: W Human Physiology Ergometry rev Fall16 17

18 . 6. Study the graphs and discuss the following: a. How do the oxygen uptake and respiratory quotient vary with time. b. VO2 max. Can you see a plateau of the curve? What is that a sign of? Questions i) Plot the VO2 max on the graph 3b above. Is there a marked inflection in the curve? If so, what does this indicate? ii) Now that the subject s maximal heart rate is know, go back to 3a and 3b and corrected the computed VO2 max. VO2 max after correction for the known maximal heart rate is l/min. iii) What happens if the subject has a higher or lower maximal heart rate than the normal population? Human Physiology Ergometry rev Fall16 18

19 Age correction table Age (years) Correction factor Age (years) Correction factor HR max= 215 max= 195 max= 180 oxygen upt ake l / mi n over - est i mat ed max accor di ng to table max oxygen upt ake at max hear t r at e 180 under - est i mat ed max oxygen upt ake at max hear t r at e 215 Figure 7. Maximal heart rate differs between different individuals which can result in wrong estimates of maximum oxygen uptake. Thus, someone with a higher heart rate than normal will have an underestimation of maximum oxygen uptake while a person with a lower heart rate than normal will have an overestimation of maximum oxygen uptake (Taken from Konditionstest på cykel, Anderson et al., 1997). Human Physiology Ergometry rev Fall16 19