Content Display Laboratory Unit : Lab 2 - Measurement of Oxygen KINE xxxx Exercise Physiology 6 Laboratory Unit 2 Lab 2 - Measurement of Oxygen 1 LAB2P1 - Introduction The goal of lab 2 is to facilitate understanding of how whole-body oxygen consumption (VO2) is measured. Measuring the rate at which oxygen is consumed is a powerful tool in understanding a person s metabolism at rest and especially during exercise. VO2 reflects the contribution of aerobic metabolism to the total energy input. There is no similar variable that can be measured to indicate the contribution of anaerobic metabolism. This lab will focus on aspects of measuring VO2. In another lab we will work with specific responses of VO2 in different situations. Contents of Lab 2: Description Introduction 1 Learning Objectives 2 List of Abbreviations 3 Page Overview of Equipment 4-13 Measurement of Whole Body VO2 14-16 Quiz 17 Measurement of Whole Body VO2 (cont) 18-19 Quiz 20 Measurement of Whole Body VO2 (cont) 21-25 Quiz 26 Measurement of Whole Body VO2 (cont) 27-29 Quiz 30 Measurement of Whole Body VCO2 31-32 Quiz 33 Standardization of Gas Volumes (STPD Conditions) 34-35 Computerized Measurement Systems 36 Lab Assignment 37 2 LAB2P2 1 of 26 5/17/2001 3:58 PM
- Learning Objectives After completion of this lab the student should be able to: 1. List basic equipment that is needed to measure oxygen consumption. 2. Define abbreviations commonly used in pulmonary gas exchange measurements. 3. List variables that must be measured in order to determine oxygen consumption. 4. Discuss the basic concept of VO2 as the difference between volume of oxygen breathed in and volume of oxygen breathed out. 5. Discuss the basic concept of VCO2 as the difference between the volume of carbon dioxide breathed in and the volume of carbon dioxide breathed out. 6. Discuss the concept of expressing gas volumes such as VO2 related to a standard set of conditions, including why this is necessary. 7. Given pertinent data, calculate VO2 and VCO2. NOTE: You are not expected to memorize specific equations presented in this lab. You are expected to be able to use equations in calculations and to understand the concepts that related to the equations. 3 LAB2P3 - List of Abbreviations 2 of 26 5/17/2001 3:58 PM
Below is a list of common abbreviations used in discussing measurement of oxygen consumption. These abbreviations are used in this lab and throughout the course. Abbreviations are part of the vocabulary of a discipline. Just like learning vocabulary in the study of a foreign language, it is essential that you become familiar with these common definitions (and others that will come up in the course). This will greatly facilitate your studying and learning of the concepts. An important note: As stated below, the letter "V" is the abbreviation for "volume." Sometimes we will be interested in the total volume of a gas, such as the total volume of oxygen consumed by a person (e.g., in liters). More often, we want to know the rate at which some gas is flowing or being used, such as the rate at which oxygen is being consumed by a person (e.g., in liters per minute). According to standard use, a dot is placed over the V to indicate a rate of flow, distinguishing it from volume (a V with no dot). For example, to indicate a rate of flow or use of oxygen, the following symbol is used: For technical simplicity in this course, I will not put dots over Vs (or other letters) to indicate rates. Rather, I will use V for both volume and flow rate, and I will indicate which variable is intended by the unit (e.g., V = 75 liters, a volume, and V = 75 liters per minute, a rate of flow. V - volume or rate of flow of a gas. VO2 - volume of oxygen consumed or volume of oxygen consumed per minute. VCO2 - volume of carbon dioxide produced or volume of carbon dioxide produced per minute. VI - volume of air inspired or volume of air inspired per minute. VE - volume of air expired or volume of air expired per minute. FIO2 - fraction of oxygen in inspired air. FEO2 - fraction of oxygen in expired air. FICO2 - fraction of carbon dioxide in inspired air. FECO2 - fraction of carbon dioxide in expired air. FIN2 - fraction of nitrogen in inspired air. FEN2 - fraction of nitrogen in expired air. 3 of 26 5/17/2001 3:58 PM
4 LAB2P4 - Overview of Equipment In this section you will be introduced to the basic pieces of equipment that are used in many systems for measuring whole-body oxygen consumption. There are many possible systems using combinations of different individual pieces of equipment. The pieces of equipment presented here are basic items that are typical of traditional systems that can be used in a simple, manual mode. These can also be interfaced with a computer to have more automated systems. In addition, there are a number of highly automated all-in-one systems that range in cost from about $10,000 to about $100,000. 5 LAB2P5 - Overview of Equipment (cont) Gasometer: Shown in the picture below is a Collins 120-liter gasometer. Literally a "gas measurer," the gasometer measures gas volumes very accurately. Gas is stored inside the cylinder that raises and lowers. In the left-hand view, the cylinder is empty. In the right-hand view there is gas being stored inside the elevated inner cylinder. Gas in this cylinder is sealed from the environment by water in the outer cylinder. Gas volume is determined by the difference in heights of the cylinder at the beginning and end of measurement. The Collins gasometer can be used for directly collecting a sample of expired air from a subject over a timed period. Volume of the sample can be determined, and then a portion of the sample can be run through gas analyzers to determine percentages of oxygen and carbon dioxide. 6 LAB2P6 4 of 26 5/17/2001 3:58 PM
- Overview of Equipment (cont) Dry gas meter. A dry gas meter, just like those used to measure the use of natural gas in homes and buildings, can be used to measure volumes of gases breathed by a subject. These are usually used only on the inspired side of the subject; that is, the subject breathes in room air through the meter. Breathing out through the meter results in collection of moisture in the meter, which may interfere with its functioning and will shorten its useful life. Also, it is difficult to disinfect the meter, so it would not be good to use the meter on the inspired side after it has been used on the expired side. Volumes are determined by the difference between starting and ending readings on the meter dial. 7 LAB2P7 - Overview of Equipment (cont) Douglas-type gas collection bags. Shown is a 120-liter plastic bag with a valve that controls access of gas into and out of the bag. These bags allow simple collection of expired air in many settings, and then gas can be stored in the bags for hours before analysis, if necessary. These bags are only useful for collecting and storing gas samples. Volume of gas in the bag must be measured by another instrument, such as the Collins gasometer. 8 LAB2P8 5 of 26 5/17/2001 3:58 PM
- Overview of Equipment (cont) Two-way nonrebreathing valve assembly. The valve assembly shown allows very high flow rates, such as occur during intense exercise, with little resistance. This valve assembly controls the direction of air flow so all inspired air comes from one side (the left side in this picture), with no expired air going back in that direction. All expired air goes out the other direction (to the right in this picture) without mixing with inspired air (i.e., no expired air is "rebreathed"). IN >>> >>> OUT An exploded view of the nonrebreathing valve assembly is shown below. 9 LAB2P9 6 of 26 5/17/2001 3:58 PM
- Overview of Equipment (cont) Direction of gas flow is controlled by the two one-way check valves that the technician is holding in the picture. The pictures below are close-ups of these one-way check valves. In the left-hand picture, she is able to open the check valve by applying gentle finger pressure in the direction shown, but in the right-hand picture the valve does not open in the opposite direction. These two check valves working in tandem enable the nonrebreathing valve assembly to allow air to be inspired from only one side and air to be expired to only the other side. When this valve assembly is used, all breathing must be done via the mouth, through the large mouthpiece shown attached to the valve assembly, and the nose must be clamped. Facemask valve assemblies are available that allow breathing through both the mouth and the nose, and no mouthpiece is required. No matter what type of breathing valve and apparatus are used, it is essential that air flow not be restricted, absolutely no air escape from the system, and the subject feel comfortable with the system. 10 LAB2P10 7 of 26 5/17/2001 3:58 PM
- Overview of Equipment (cont) Electronic gas analyzers. Most systems for measuring VO2 use electronic oxygen and carbon dioxide analyzers, as shown. These measure the percent oxygen and carbon dioxide, respectively, in a mixture of gases (usually expired air). Many different models are available. Electronic analyzers are usually the most expensive single item of equipment in the complete system, but they are easy to use, rapid, and accurate. A small sample of gas is pulled through the analyzers by a vacuum pump, and the percent concentrations of oxygen and carbon dioxide are displayed on the digital meters (or can be read by a computer interfaced with the system). Samples can be taken directly from the Collins gasometer or a Douglas bag, or expired air can be sampled continuously from a mixing chamber to give averaged gas concentrations over a period of time. Samples are passed through a drying canister before entering the analyzers to remove all water from the sample. This is done for two reasons: (a) To reduce the number of gases in the mixture to three; oxygen, carbon dioxide and nitrogen. By doing this, only two of the gases have to be measured, and the third can be calculated as the remaining difference. (b) To keep tubes from becoming clogged by moisture that condenses or by sediment in the moisture. It is important to calibrate analyzers frequently using precision gas mixtures of known concentrations. Calibration is the process of checking the accuracy of an instrument's measurements against some standard and, if possible, adjusting the instrument to measure accurately. Electronic gas analyzers can be adjusted to precisely match precision calibration gases of known concentrations. 11 LAB2P11 8 of 26 5/17/2001 3:58 PM
- Overview of Equipment (cont) Miscellaneous equipment. Various additional small items of equipment are essential to complete the oxygen flow measurement system. (a) Large, low resistance hoses are used to connect various parts of the system, such as the nonrebreathing valve to the gasometer. (b) Noseclips are used to prevent airflow through the nose when all air is to be breathed through the mouth. 12 LAB2P12 9 of 26 5/17/2001 3:58 PM
- Overview of Equipment (cont) (c) In order to standardize gas volumes to standard conditions (discussed later in the lab), the following are needed: a barometer for measuring atmospheric pressure, a thermometer for measuring the temperature of all gas volumes, a hygrometer for measuring relative humidity or amount of water vapor in a gas mixture. 13 LAB2P13 - Overview of Equipment (cont) (d) A headgear or other apparatus for supporting the nonrebreathing valve and connecting hose(s). (e) Materials for cleaning and disinfecting mouthpieces, valves and hoses. 14 LAB2P14 10 of 26 5/17/2001 3:58 PM
- Measurement of Whole Body VO2 Oxygen is consumed by the body in aerobic metabolism. In fact, oxygen is used and converted to water (by combining with hydrogen) in what may be considered the very last chemical reaction of the many reactions that make up aerobic metabolism. The rate at which the entire series of reactions takes place is to a large extent dependent on the rate at which oxygen is converted to water, that is, consumed. In the extreme case, if oxygen is not available for this last reaction, all of the reactions quickly stop, and ATP cannot be formed by aerobic metabolism. We measure whole-body oxygen consumption by analyzing air breathed. This is referred to as "pulmonary gas exchange" because it involves exchanging gases (i.e., oxygen and carbon dioxide) in the lungs. Such pulmonary gas exchange measurements reflect aerobic metabolism in all cells of the body. During vigorous exercise, oxygen consumed by exercising skeletal muscles dominates whole-body VO2. 15 LAB2P15 - Measurement of Whole Body VO2 VO2 may be described as the difference between the volume of oxygen breathed into the body (VIO2) and the volume of oxygen breathed out of the body (VEO2). This can be summarized: (1) VO2 = VIO2 - VEO2 In each minute, we take in a given volume of oxygen and exhale a smaller volume of oxygen. The reason the volume of exhaled oxygen is less is because some oxygen was taken out of the air in the lungs, carried by the blood to cells throughout the body, and used (consumed) in aerobic metabolism. Conceptually, then, measurement of VO2 is simple: Measure VIO2 and VEO2 and the difference is VO2. 16 LAB2P16 11 of 26 5/17/2001 3:58 PM
- Measurement of Whole Body VO2 (cont) To determine the volume of any gas in a mixture of gases, we multiply the total volume of the mixture by the fraction (the decimal form of the percent) made up by the gas of interest. For example, normal atmospheric air consists of 20.93% oxygen, 0.03% carbon dioxide, and 79.04% nitrogen. (Actually there are very small fractions of other gases, but in physiology these are lumped together with nitrogen because they are physiologically inert.) So, if we have a container that has 100 liters of air in it, we know that this container has 20.93 liters (100 L x 0.2093) of oxygen, 0.03 liters (100 L x 0.0003) of carbon dioxide, and 79.04 liters (100 L x 0.7904) of nitrogen. 17 LAB2P17 INLINE QUIZ 18 LAB2P18 - Measurement of Whole Body VO2 (cont) The volume of oxygen inspired equals the total volume of air inspired (VI) multiplied by the fraction of oxygen in the inspired air (FIO2),and the volume of oxygen expired equals the total volume of air expired (VE) multiplied by the fraction of oxygen in the expired air (FEO2): (2) VIO2= V I x FIO2 (3) VEO2 = VE x FEO2 If we substitute these expressions in Equation 1, VO2 may be calculated as: (4) VO2 = (VI x FIO2) (VE x FEO2) Remember that the fraction of oxygen in normal atmospheric air is a constant 0.2093. Therefore, as long as we are measuring VO2 while a person is breathing normal air, Equation 4 may be written: (5) VO2 = (VI x 0.2093) (VE x FEO2) This shows that we can determine VO2 by measuring three other variables: the total volume of air inspired (VI), the total volume of air expired during the same time period (VE), and the percent or fraction of oxygen in the air breathed out (FEO2). 12 of 26 5/17/2001 3:58 PM
19 LAB2P19 - Measurement of Whole Body VO2 (cont) The picture shows measurement of pulmonary gas exchange variables. The subject is inspiring through a dry gas meter, by which VI is determined, and expiring into a Collins gasometer, by which VE is determined. Let s assume that VI = 48.3 L/min and VE = 46.9 L/min. Also, let s assume that we analyzed the expired air in the gasometer and FEO2 = 0.1720. We can calculate this person s VO2. VO2 = (VI x 0.2093) (VE x FEO2) = ([48.3 L/min] x 0.2093) ([46.9 L/min] x 0.1720) = 2.0 L/min Note that this person was taking in 10.1 L of oxygen per minute and breathing out 8.1 L of oxygen per minute. 20 LAB2P20 21 LAB2P21 13 of 26 5/17/2001 3:58 PM
- Measurement of Whole Body VO2 (cont) Although measurement of VO2 is really simple with measurement of both VI and VE, most laboratories use a system that measures only VI or VE. We still need to know both, and we can t assume that they are the same (VI and VE are rarely equal). Fortunately, we can calculate one from the other. This is done by what is known as the Haldane transformation, as follows: (6) VI = (VE x FEN2) / FIN2 (7) VE = (VI x FIN2) / FEN2 You can see that these conversions require knowledge of fractions of nitrogen (N2) in both the inspired air and the expired air. As long as we are measuring in normal atmospheric air, FIN2 = 0.7904. FEN2 must be determined. In most measurement systems, fractions of both oxygen and carbon dioxide are measured in expired air, and the remainder is known to be nitrogen (if the sample has been dried so no water vapor is in it). 22 LAB2P22 - Measurement of Whole Body VO2 (cont) If we are measuring VO2 in normal atmospheric air, after all substitutions and algebraic simplifications are done, we end up with the following equations. For calculating VO2 when we measure minute volume of ventilation on the inspired side: (8) VO2 = VI x (0.2093 [0.7904 x FEO2 / FEN2]) For calculating VO2 when we measure minute volume of ventilation on the expired side: (9) VO2 = VE x ([0.2648 x FEN2] - FEO2) You can see that with either method of measuring VO2, three variables must be known: (a) FEO2 This is measured by running a sample of expired air through an oxygen analyzer. (b) FEN2 This is most commonly determined by measuring both FO2 and FCO2 in a sample of expired air with gas analyzers and taking the remainder as nitrogen (i.e., FN2 = 1.00 FO2 FCO2) (c) Either VI or VE This is measured with a dry gas meter, a 14 of 26 5/17/2001 3:58 PM
(c) Either VI or VE This is measured with a dry gas meter, a Collins gasometer, an electronic flow meter, or another similar device. 23 LAB2P23 - Measurement of Whole Body VO2 (cont) Let's practice using these equations to calculate VO2. EXAMPLE: This example uses values that are typical of a person at rest. The expired gas from the person in this picture is collected in the Collins gasometer for 3 minutes. The measured volume of the expired gas (VE) is 20.5 liters. Electronic gas analyzers are used to sample the gas and determine the fractions of oxygen and carbon dioxide that make up the expired gas sample. The analyzers read the fractions as 18.00% oxygen (FEO2 = 0.1800) and 2.30% CO2 (FECO2 = 0.0230). We want to calculate the oxygen this person consumed during this three-minute measurement period. In order to calculate VO2 using measured VE, we will use the equation VO2 = VE x ([ 0.2648 x FEN2] FEO2) In order to use this equation, we also need the fraction of nitrogen in the person s expired air (FEN2). Recall the fraction of nitrogen in expired air can be calculated by subtracting the fractions of oxygen and carbon dioxide in expired air from one. FEN2 = 1 FEO2 FECO2 FEN2 = 1 0.180 0.023 = 0.797 Substituting into our equation for VO2, we find VO2 = 20.5 x ([0.2648 x 0.797] 0.180) VO2 = 0.64 liters in this three-minute period, or 0.21 L/min. 24 LAB2P24 15 of 26 5/17/2001 3:58 PM
- Measurement of Whole Body VO2 (cont) EXAMPLE. This example uses values that are typical of a person doing exercise of moderate intensity. The subject for whom VO2 was measured at rest in the previous example is now walking briskly on a motorized treadmill at a speed of 3.7 mph or about 16 min/mile. We will measure her VO2 during this bout by measuring the volume of inspired air over a one-minute period and measuring the gas fractions in her expired air during that same period. VI as measured by the flowmeter during this minute was 22.00 liters of air. FEO2 was 0. 172 and FECO2 was 0.029, both measured by analysis of the subject s expired air. Again we must calculate FEN2. FEN2 = 1 FEO2 FECO2. FEN2 = 1-0.172 0.029 FEN2 = 0.799 (Eq. 8) VO2 = VI x (0.2093 [0.7904 x FEO2 / FEN2]) VO2 = 22.00 x (0.2093 [0.7904 x 0.172 / 0.799]) VO2 = 0.86 L Since 0.86 liter of oxygen was consumed in one minute, we can say the rate of oxygen consumption was 0.86 L/min. 25 LAB2P25 16 of 26 5/17/2001 3:58 PM
- Measurement of Whole Body VO2 (cont) EXAMPLE. This example uses values that are typical of a highly trained endurance athlete exercising at a high intensity, such that VO2 max is elicited. Our subject is a male triathlete who had recently completed an Ironman event. In this example he is running on a motorized treadmill at a speed of 268 meters per minute (6 minutes per mile) and up a positive 3% grade. VE will be measured by collecting a 30-second sample of his expired air in the Collins gasometer. The gas fractions in this sample will then be measured by the electronic gas analyzers. The 30-second sample had the following values: VE = 59.8 L FEO2 = 0.166 FECO2 = 0.044 FEN2 = 1 FEO2 FECO2 FEN2 = 1 0.166 0.044 FEN2 = 0.790 VO2 = VE x ([0.2648 x FEN2] FEO2) VO2 = 59.8 x ([0.2648 x 0.790] 0.166) VO2 = 2.58 L Since this sample duration was 30 seconds, his rate of oxygen consumption was 2.58 liters / 0.5 minutes or 5.15 L/min. 26 LAB2P26 27 LAB2P27 17 of 26 5/17/2001 3:58 PM
- Measurement of Whole Body VO2 (cont) VO2 is expressed in two types of units: either as the total, absolute volume of oxygen consumed per minute (i.e., L/min or ml/min), or as the relative volume of oxygen consumed adjusted for body weight (i.e., ml/kg/min). Both units are useful, depending on what we want to know. Sometimes we want to know the total volume of oxygen consumed, such as when we want to convert oxygen consumed to kilocalories of energy to determine the total caloric cost of a bout of exercise. In such cases, we use L/min or ml/min. But the total absolute volume of oxygen consumed is affected by body size. In general, a larger person will consume more oxygen because he/she has more cells. Remember, oxygen consumption takes place in individual cells in the body. So, when we want to eliminate the effect of body size, we express VO2 as ml/kg/min. One example is when we compare VO2 values of athletes in different sports. Often these athletes differ greatly in body size, so we eliminate the effect of body size on VO2 values to make comparison more valid and meaningful. It is essential that you be proficient at converting between L/min and ml/kg/min. This is done as follows. To convert L/min to ml/kg/min: ml/kg/min = (L/min) x 1000 / body weight in kilograms To convert ml/kg/min to L/min: L/min = (ml/kg/min) x body weight in kilograms / 1000 (Remember that weight in kilograms = weight in pounds / 2.205) 28 LAB2P28 18 of 26 5/17/2001 3:58 PM
- Measurement of Whole Body VO2 (cont) CALCULATION EXAMPLE 1: Suppose the triathlete on Page 22 has a body weight of 75 kg. To find his relative VO2 in ml/kg/min, we divide his absolute VO2 of 5.15 L/min by his body weight in kilograms, then multiply by 1000. Relative VO2 = (5.15 L/min / 75 kg) x 1000 ml/l Relative VO2 = 68.7 ml/kg/min CALCULATION EXAMPLE 2: Suppose an oarsman paddling a skull has a relative VO2 of 28.5 ml/kg/min. If his body weight is 200 lb, find his absolute VO2 in liters per minute. First, we will convert 200 lb to kg: 200 / 2.205 = 90.7 kg. Absolute VO2 = (relative VO2 x body weight in kg) / 1000 Absolute VO2 = (28.5 x 90.7) / 1000 Absolute VO2 = 2.59 L/min 29 LAB2P29 - Measurement of Whole Body VO2 (cont) CALCULATION EXAMPLE 3: While running on a treadmill, a runner who weighs 70 kg. has his inspired air flow rate measured. To calculate his relative VO2 during this bout, his expired gas was concurrently analyzed for fractional content of O2 and CO2. The measurements were as follows: VI = 57.3 L/min FEO2 = 0.155 FECO2 = 0.049 We wish to calculate his absolute and relative VO2. FEN2 = 1-0.155 0.049 FEN2 = 0.796 Absolute VO2 = VI x (0.2093 [0.7904 x FEO2 / FEN2]) Absolute VO2 = 57.3 x (0.2093 [0.7904 x 0.155 / 0.796]) Absolute VO2 = 3.18 L/min Relative VO2 = (3.18 L/min / 70 kg) x 1000 ml/l Relative VO2 = 45.5 ml/kg/min 19 of 26 5/17/2001 3:58 PM
Relative VO2 = 45.5 ml/kg/min 30 LAB2P30 inline quiz 31 LAB2P31 - Measurement of Whole Body VCO2 VCO2 is the volume of carbon dioxide produced and expired by the body, usually expressed per minute. Although usually VO2 is of primary concern, often VCO2 is important to know also. It is easily calculated from the same measurements that are done to determine VO2. Conceptually, VCO2 is the difference between amount of CO2 expired and the amount inspired. Note that this is the opposite of oxygen, though the concept is the same. With oxygen, we take in a relatively large amount, consume some, and expire a smaller amount. With carbon dioxide, we take in a small amount (usually close to none, because there is so little CO2 in normal air), we produce CO2 in metabolism and other chemical reactions in body cells, and we breathe out a larger amount than taken in. So: (10) VCO2 = VECO2 VICO2 The final equations that are used to calculate VCO2 in most measurement systems are as follows: For calculating VCO2 when we measure minute volume of ventilation on the inspired side: (11) VCO2 = VI x ([0.7903 x FECO2 / FEN2] 0.0003) For calculating VCO2 when we measure minute volume of ventilation on the expired side: (12) VCO2 = VE x (FECO2 [FEN2 x 0.0004]) VCO2 is almost always presented in units of L/min or ml/min and almost never as ml/kg/min (as VO2 often is). 32 LAB2P32 20 of 26 5/17/2001 3:58 PM
- Measurement of Whole Body VCO2 (cont.) EXAMPLE 1: In a 30 second period, a person has an expired volume of 38 L. Analysis of the expired gas shows FEO2 = 0.171 FECO2 = 0.043 To calculate VCO2 in this example, first we must calculate FEN2. Recall that FEN2 = 1 - FEO2 - FECO2 FEN2 = 1-0.171-0.043 FEN2 = 0.786 VCO2 = VE x (FECO2 - [FEN2 x 0.0004]) VCO2 = 38 x (0.043 - [0.786 x 0.0004]) VCO2 = 1.62 L in the 30-second period. EXAMPLE 2: Suppose the same subject is performing the same exercise but the inspired air flow rate is being measured and gas fractions are being measured in expired air. VI = 75.6 L/min. We can calculate VCO2 in this case. FEO2 = 0.171 FECO2 = 0.043 FEN2 = 1-0.171-0.043 FEN2 = 0.786 VCO2 = VI x ([0.7903 x FECO2 / FEN2] - 0.0003) VCO2 = 75.6 x ([0.7903 x 0.043 / 0.786] - 0.0003) VCO2 = 3.25 L/min 33 LAB2P33 34 LAP2P34 21 of 26 5/17/2001 3:58 PM
- Standardization of Gas Volumes (STPD Conditions) It is common practice in exercise physiology to correct VO2 and VCO2 values to a set of standard conditions known as STPD conditions. STPD stands for standard temperature, pressure, dry. The reason for this is that the volume of any gas is affected by the atmospheric pressure pressing in on it, its temperature, and the amount of water vapor in the sample. Let s assume, for example, that we put 100 liters of air in a Douglas bag in the lab at The University of Texas at Tyler. If we would take this bag to Denver, the mile-high city, the gas would expand so there would be more than 100 liters in the bag, because of a lower atmospheric pressure at the higher altitude. If we would take the bag to Death Valley, the volume would shrink to less than 100 L, because of a greater atmospheric pressure pressing on the bag. Also, let s assume the temperature of the gas was 20 degrees Celsius when we originally put the 100 L in the bag. If the temperature were 0 degrees when we take the bag to Denver, that would make the volume shrink; if the temperature were 40 degrees in Death Valley, that would make the volume expand. Finally, if we would take all the water vapor out of the original 100-L sample, the volume would be reduced; if we saturated the sample so it held all the water vapor it possibly could, the volume would increase. 35 LAP2P35 22 of 26 5/17/2001 3:58 PM
- Standardization of Gas Volumes (STPD Conditions) (cont) In short, it would be very difficult to compare measurements made under different conditions, especially conditions of different altitude and pressure, as well as temperature. Therefore, physiologists measure the ambient conditions of barometric pressure, and the temperature and vapor pressure of gas samples; these are referred to as ATPS conditions (ambient temperature, pressure and saturation). They then correct measured volumes to STPD conditions. This allows valid comparisons of VO2 and VCO2 values measured under all conditions, including measurements of skiers at an altitude of 12,000 feet, divers 50 feet below sea level, runners competing in the desert heat of Death Valley, and sledders in the Arctic. Calculations of correction factors to standardize gas volumes to STPD conditions are easy to do, but we will not do these in this course. It is important, however, that you know that this correction is essential and that it is standard practice. You will usually see in research literature reports of VO2 (STPD). It is also important that you realize that measurement of VO2 requires determination of barometric pressure and the temperature and vapor pressure of any gas volume that is measured. 36 LAP2P36 23 of 26 5/17/2001 3:58 PM
- Computerized Measurement Systems In this lab you have been introduced to the fundamentals of measuring whole-body VO2 and VCO2 by pulmonary gas exchange. I hope you can see that the underlying concepts and the basic, manual procedures are straightforward and not difficult. And measurements can be very accurate if technicians are trained and pay attention to detail. Of course, a certain amount of rather expensive equipment is needed to make these measurements, especially the gas analyzers. The techniques I have described in this lab and the calculations involved are labor-intensive, however, and subject to technician error. So, most laboratories use computerized, automated systems for these measurements. Computerized systems allow essentially unlimited samples to be measured in succession, with rapid calculations of data and instantaneous feedback. Also, they require little technician involvement. They are not necessarily or automatically accurate, however. These instruments must be calibrated to assure that they are accurate and stable. And of course, these automated systems cost more. Most of the computerized systems are based on the concepts and calculations we have dealt with in this lab. If you have the opportunity to work with such a system, the knowledge you have gained from this lab will help you understand where the measurements are coming from. 37 LAB2P37 - Lab Assignment Using the formulas presented in this lab, make the following calculations. 1. While riding a stationary bicycle ergometer, the following steady-state values were obtained on a subject whose body weight was 74 kg: VI = 40.16 L/min FEO2 = 0.168 FECO2 = 0.04 Based on this information, calculate this subject's steady-state (a) absolute VO2 in L/min (b) relative VO2 in ml/kg/min (c) VCO2 in L/min 24 of 26 5/17/2001 3:58 PM
2. While performing arm-crank ergometry, a patient's expired air was collected in a Douglas bag. The collection period was 40 seconds and the patient's weight was 85 kg. The following values were obtained on the air in the Douglas bag: V = 12.0 L FEO2 = 0.171 FECO2 = 0.036 Based on this data for this 40-second period, calculate the subject's (a) VE in L/min (b) absolute VO2 in L/min (c) relative VO2 in ml/kg/min (d) VCO2 in L/min Submit the problems and their solutions to the instructor via attachment to e-mail. The attachment should include The problem restated as it appears on this page All formulas used in its solution All formulas with appropriate values substituted into the formulas The values asked for in the problem In short, your solutions to the problems should look like the solutions to example problems presented in this lab. The subject line of the e-mail used to submit this assignment should be "your name-lab 2". This concludes Lab 2. Cancel Key: 25 of 26 5/17/2001 3:58 PM
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