Recording established using the VO2 and RER graph template file (h19.gtl)

Transcription

1 Updated BSL PRO Lesson H19: VO 2 and RER Measurement Recording established using the VO2 and RER graph template file (h19.gtl) Overview Oxygen Consumption (VO 2 ) and Respiratory Exchange Ratio (RER) Real-time Oxygen Consumption (VO 2 ) and Respiratory Exchange Ratio (RER) measurements can be obtained using the MP3x System with the Gas-System2 module and some airflow accessories. When performing tests of this kind, many factors exist to confound the measurement. For example, it may be reasonable to think that the volume of expired air is always the same as inspired air, but this is only true when the volume of carbon dioxide expired is equal to the volume of oxygen consumed. The inspired and expired volumes are equal only when the RER equals one. RER is defined as VCO 2 produced divided by VO 2 (where V is volume). Accordingly, when performing these measurements, precise determination of inspired and expired volumes and accurate assessment of the gas concentration level are required. The Gas-System2 measures O 2 and CO 2 concentrations in vapor. When the subject inspires, air will be drawn into the Gas-System2 through the SS11LA airflow transducer. The SS11LA is placed on the inspiration side to eliminate any effects associated with Page 1 of 16

2 expired air humidity (see Hardware Setup for more detail). When the subject expires, air will be directed to the Gas-system2 module. The Gas-System2 is designed to work with saturated expired air. When using a mixing chamber to average O 2 and CO 2 concentrations over several breaths and measuring these changes for arbitrarily high breathing rates, there is no performance degradation. Accordingly, a mixing chamber (such as the Gas-System2 utilizes) is typically recommended for quick, accurate and easy metabolic analysis. IMPORTANT CONCEPT! The non-rebreathing T valve directs only expired air to the Gas-System2. Because only expired air is directed to the module, the system acts to average respiratory outflows. This averaging effect causes the CO 2 and O 2 concentrations to vary in accordance to the mean values resident in a few expired breaths. The size of the system s chamber determines the extent of the averaging effect. For example, if the subject s expired breath volume is 0.5 liters, the Gas-System2 s chamber will average about 10 expired breaths. Definitions Click here for definitions of abbreviations used in this lesson and the calculation channel Expression formulas used for VO 2 and RER. Objectives 1. To obtain absolute VO 2 and RER values for a subject at rest (optional segments include hyperventilation and recovery from exercise). 2. To demonstrate the relationship between VO 2 and RER. NOTE: The Gas-System2 module is intended for VO2 and RER studies ranging from resting to moderate exercise. For prolonged or vigorous exercise studies where CO2 levels may exceed 5%, BIOPAC recommends the AcqKnowledge Research system with O2100C and CO2100C gas sensing modules. Equipment BIOPAC Gas Analysis System (GASSYS2-EA) BIOPAC Pneumotach Airflow Transducer [High Flow] (SS11LA) BIOPAC Calibration Syringe (AFT26 or AFT6) BIOPAC 22 mm Non-Rebreathing T Valve (AFT22) BIOPAC Rigid Coupler (AFT11E) for T-valve to tubing BIOPAC Coupler (AFT11C) for T-valve to calibration syringe BIOPAC Smooth Bore Tubing-35 mm (AFT7) BIOPAC Disposable Nose Clip (AFT3) BIOPAC Disposable Mouthpiece (AFT2) BIOPAC Disposable Bacterial Filters (AFT1) requires 2 filters Computer running Windows XP or higher, or Mac OS X Biopac Student Lab PRO software BIOPAC Data Acquisition Unit (MP36/MP35/MP30) OPTIONAL: BIOPAC Calibration Gas Cylinder (16% O 2, 4% CO 2 ), with regulator and tubing The following measures are also required: Ambient temperature in C Ambient barometric pressure in mmhg Pressure of water vapor at ambient temperature = 22.4 mmhg Page 2 of 16

3 Setup Hardware The Gas-System2 sensors are factory calibrated prior to shipping. The O 2 sensor is a zirconia solid electrolyte with a % sensing range and an estimated 5-year lifetime. It runs hot, which helps to burn off humidity. The CO 2 sensor uses a humidity-repellant (hydroponic) membrane and has a sensing range of 0-5%. It uses non-dispersive infra-red diffusion with single-beam IR and a self-calibrating algorithm. It also runs hot, which helps to burn off humidity. 1. The Gas-System2 module is supplied with a 5 4 amp wall adapter. Plug the adapter into the main power supply and insert the adapter plug into the DC Input on front of the Gas-System2 module. 2. Flip up the power switch on the Gas-System2 to turn it "ON." o The unit should warm up for at least five minutes before calibration, so it is suggested that you turn it on now and then complete setup. 3. Plug the transducers into the MP3X as follows: Transducer MP3X CH # SS11LA CH 1 O2 line (from the Gas-System2) CH 2 CO2 line (from the Gas-System2) CH 3 Page 3 of 16

4 4. Turn on the MP unit (assuming the AC100A power adapter has already been connected). 5. Connect the airflow accessories as follows: Air Flow Accessory AFT1 filter SS11LA transducer AFT22 non-rebreathing T-valve AFT11E coupler AFT7 tubing AFT26 or AFT6 calibration syringe AFT11C coupler Connects to SS11LA transducer, on the "Inlet" side AFT22 non-rebreathing T-valve AFT11E coupler AFT7 tubing Gas-System2 inlet (back side) AFT11C coupler AFT22 non-rebreathing T-valve Note: The above setup uses the AFT26 or AFT6 calibration syringe. For recording, you must replace the calibration syringe with an AFT1 filter and an AFT2 disposable mouthpiece (connected to each other and to the AFT22 T-Valve). Page 4 of 16

5 AFT7 tubing to Gas-System2 inlet 6. Pump the calibration syringe through enough cycles to fill the chamber with ambient air. o AFT26, pump 3-4 times. o AFT6, pump times. Software 1. Launch the BSL PRO software on the host computer. The program should create a new "Untitled1" window. 2. Open the VO 2 and RER Template by choosing File > Open > choose Files of type: Graph Template (*GTL) > File name: H19 V02 & RER.gtl The template will establish the required settings. This particular setup will provide a reading that, at any point in time, indicates the absolute volume of oxygen consumed, carbon dioxide produced, and the respective respiratory exchange ratio in the last 60 seconds. Units are liters because it is a volume measure, not a flow rate. 3. Save As the desired file name. Calibration The following calibration steps are outlined below: A. Calibrate flow transducer B. Calibrate O 2 channel (CH2) C. Calibrate CO 2 channel (CH3) D. Normalize moist gas to volume occupied by dry gas at 0 C, 760 mm. E. Optional: Calibrate for time interval (template is based on 60-second interval). Note: In the calculation channel formulas, the following assumed values were used for gas concentrations in normal atmosphere (chamber flooded with ambient air): 0 2 = 20.93% CO 2 = 0.04% N 2 = 79.03% The optional Stage 2 gas calibration is not required, but can be performed using the small line inlet on the back panel of the Gas-System2 module. If you introduce calibration gases into the chamber, adjust the calculation channel expressions for the real gas values. If you perform a gas calibration, use the following ranges: Flow (inspired): calibrate within the range of 0 to 13 liters/sec O 2 concentration: calibrate in range of 21% to 16% O 2 CO 2 concentration: calibrate in range of.04% to 4% CO 2 Page 5 of 16

6 Flow 1. Select MP3X > Setup Channels. 2. Click the wrench icon for CH Click the Scaling button. 4. Hold the Calibration Syringe such that the SS11LA hangs from it in an upright position. 5. Click on the Cal1 button. 6. Subtract 3,000 from the Cal1 input value and enter the result in Cal2 input value (Cal2 input value should be 3,000 less than Cal1 input value). 7. Confirm Cal1 scale value= 0 and Cal2 scale value= Click OK. 9. Set the equipment down. Page 6 of 16

7 O 2 Per Setup, the chamber should have been flooded with ambient air prior to O 2 calibration! 1. Click the wrench icon for CH Click the Scaling button. 3. Click the Cal2 button. 4. Enter into the Cal2 scale value. 5. Confirm both Cal1 input value= 0 and Cal1 scale value=0. 6. Click OK. CO 2 Per Setup, the chamber should have been flooded with ambient air prior to CO 2 calibration! 1. Click the wrench icon for CH Click the Scaling button. 3. Click the Cal1 button. 4. Enter 0.04 into the Cal1 scale value. 5. Add 10 to the Cal1 input value and enter the result as Cal2 input value. 6. Confirm Cal2 scale value= Click OK. Note: The sensor output is 10 mv per 1% C0 2. With proper calibration, if the sensor rails, it will read as 5% CO 2. Page 7 of 16

8 OPTIONAL Stage 2 Calibration (BIOPAC Calibration Gas Cylinder required) O 2 Per Setup, the chamber should NOW be flooded with a calibrated gas (16% O 2, 4% CO 2 )! 1. Click the wrench icon for CH Click the Scaling button. 3. Click the Cal1 button. 4. Enter 16 into the Cal1 scale value. 5. Click OK to dismiss scaling dialog. 6. Click OK to dismiss Input Channel Parameters dialog for CH 2. CO 2 Per Setup, the chamber should NOW be flooded with a calibrated gas (16% O 2, 4% CO 2 )! 1. Click the wrench icon for CH Click the Scaling button. 3. Click the Cal2 button. 4. Enter 4 into the Cal2 input value. 5. Click OK to dismiss the scaling dialog. 6. Click OK to dismiss Input Channel Parameters dialog for CH 3. Page 8 of 16

9 Gas Normalization Normalize moist gas to volume occupied by dry gas at 0 deg C, 760mm 1. Use this table to find the normalization factor. 2. Click the wrench icon for C3 Vis (STPD). 3. Enter the normalization factor in the formula: C2*(normalization factor) Be sure to enter the value as 0.x, with the leading decimal. 4. Click OK. Optional: Interval Only required if you change the time interval from the template, which is set for a 60-second interval. 1. Click the wrench icon for C2. Page 9 of 16

10 3. Calculate the Samples entry as follows: Integration Samples = Time Interval x Sample rate (Template setting: Integration Samples = 60 sec x 100 samples/sec = 6000 samples) 4. Enter the new Samples value. 5. Click OK. Recording This lesson records absolute volume of O 2 and CO 2 in a 60-second interval. Units are liters because this provides a volume measure, not a flow rate. If you change the time interval, you must adjust the Integrate formula. Hints for minimizing measurement error: 1. Ensure that the connections among the various pieces of equipment are fairly tight to prevent contamination via room air. 2. Try to start the recording immediately after a full exhale. This will prevent receiving results with an O 2 inspiration value less than that of the total expiration value (although the averaging will minimize the inaccuracies that this would cause). 3. It's very important that any extraneous volumes are minimized between the subject and the T-valve. Additional volumes affect the effective expired gas concentration levels. 4. The tubing must be connected to the SS11LA on the unlabeled side (that does NOT say "Inlet"). Preparation 1. Remove the calibration syringe from the transducer setup. 2. Establish the recording connections as shown below: Airflow Accessory Connects to AFT1 Filter AFT22 T-Valve (in the existing setup) AFT2 disposable mouthpiece AFT1 Filter Page 10 of 16

11 Segment 1 1. Have the subject put a nose clip on. 2. Click START in the PRO software. 3. Have the subject breathe normally for at least 2 minutes. o Subject must breathe long enough to ensure that the 5-liter mixing tank has been filled, thereby enabling it to average those breaths. o The subject should breathe into the disposable bacterial filter (AFT1) through a disposable mouthpiece attachment (AFT2). 4. Click STOP in the PRO software. Breathe through the mouthpiece Page 11 of 16

12 Optional Segments Recovery from Exercise 1. Have the subject perform several minutes of medium-to-strenuous exercise. o If desired, record the heart rate and correlate VO 2 to heart rate. 2. Click START in the PRO software. 3. Have the subject breathe normally for at least 2 minutes. 4. Click STOP in the PRO software. Hyperventilation 1. Click START in the PRO software. 2. Have the subject breathe normally for at least 1 minute. 3. Have the subject hyperventilate for at least 1 minute; enter a marker at start of hyperventilation (Esc on PC, F9 on Mac). 4. Have the subject breathe normally for at least 1 minute. 5. Click STOP in the PRO software. Notes To save recorded data, choose File menu > Save As > file type: BSL PRO files (*.ACQ) File name: (Enter Name) > Save button To erase all recorded data (make sure you have saved it first), and begin from Time 0, choose: MP menu > Setup Acquisition > Click Reset Page 12 of 16

13 Analysis The VO 2 and RER template will display channels as follows: Channel Displays Measure CH 1 Fi (inspired Air Flow) Value CH 2 O 2 E (expired O 2 ) Value CH 3 CO 2 E (expired CO 2 ) Value CH 40 (C1) N 2 E (expired N 2 ) Value CH 41 (C2) Vi (ATP) Value CH 42 (C3) VIS (STPD; inspired) Value CH 43 (C4) VES (STPD; expired) Value CH 44 (C5) VO 2 (STPD) Value CH 45 (C6) VCO 2 (STPD) Value CH 46 (C7) RER Value 1. Channels are not displayed because they are calculation channels required for conversions. You can show/hide channels by Ctrl-clicking the channel box. 2. Note that the VO 2 and RER measurements (bottom two channels) vary smoothly with time. The graphical and continuous nature of this recording and calculation method provides significant information regarding the changes of these variables over time. 3. To display measurements, click the measurement icon. 4. To display markers, click the flag icon. 5. To display grids, click the grid icon. Page 13 of 16

14 Appendix GRAPH TEMPLATE SETTINGS Click here to open a PDF of the graph template file settings. The BSL PRO Graph Template file automatically establishes the settings shown in the table. Definitions These abbreviations are used in the discussion and calculation channel Expression formulas for VO 2 and RER: ATP Concentration of gas at ambient temperature and pressure CO 2 Fi Carbon dioxide Est. concentration ambient environment: 0.04% CO 2 e = Carbon Dioxide fractional concentration in expired air Inspired air flow (ATP) N 2 Nitrogen N 2 e = Nitrogen fractional concentration in expired air N 2 e = 100 (CO 2 e + O 2 e) O 2 Pb PH 2 0 RER STPD Oxygen Est. concentration in ambient air: 20.93% O 2 e = Oxygen fractional concentration in expired air Est. concentration in expired breath: 16% oxygen Ambient barometric pressure (e.g. 745 mmhg) Ambient pressure of water vapor (e.g mmhg) Respiratory Exchange Ratio RER = VCO 2 / VO 2 Concentration of gas at standard temperature and pressure, dry Ta Ambient temperature (e.g. 24 deg. C) VCO 2 VO 2 Vi Volume of carbon dioxide produced (STPD) per 60-sec interval Real-time carbon dioxide production VCO 2 = (1/100)*[(Ves* CO 2 e) (Vis*.04)] Volume of oxygen consumed (STPD) per 60-sec interval Real-time oxygen consumption VO 2 = (1/100)*[(Vis*20.93) (Ves*O 2 e)] Inspired air volume (ATP) per 60-sec interval Vi = Integrate (Fi) over 60 seconds. The number of samples is equal to the time interval x sample rate (template is 60 sec. x 100 samples/sec = 6000 samples). Select "Average over samples." Vis Inspired air volume (STPD) per 60-sec interval Vis = C2 * Normalization Factor (see Table of Normalization Factors) If normalization factors are unavailable, you can use this formula: Vis = Vi*(273/(273+Ta))*((Pb-PH 2 0)/760) where Ta = ambient temperature Pb = barometric pressure PH 2 O = 22.4 mmhg (assumed value) Ves Expired air volume (STPD) per 60-sec interval Ves = (Vis*79.03) / N 2 e Note: If you change the time interval from 60 seconds, you must adjust the Vi formula. Page 14 of 16

15 Normalization Factors The following table lists the factors required to reduce volume of moist gas to volume occupied by dry gas at 0 C, 760 mm. OBR is an abbreviation for observed barometric reading, uncorrected for temperature. Fahrenheit values are roughly converted and rounded from Celsius values as T F =(9/5*T C )+32ºF. Important! All factors are 0.x, with x being the value from the table. Be sure to include the leading decimal when you complete your calculation. ºC ºF OBR Page 15 of 16

16 ºF ºC From Peters and Van Slyke, Quantitative Clinical Chemistry, vol. 11. (Methods) Baltimore: Williams and Wilkins, 1932, reprinted Page 16 of 16