Respiratory Gas Analysis

Overview:

Gas exchange occurs via simple diffusion in unicellular organisms. However, complex multicellular organisms require a respiratory system for effective gas exchange, which is integrated with the circulatory system to carry gases to and from the tissues. In humans, this system consists of the airways, the lungs, and the respiratory muscles that control the movement of air in and out of the body. Respiration serves as a means for the body to exchange gases with the atmosphere via blood. Each inhalation transports clean oxygenated air into the lungs, where molecules of oxygen diffuse into the blood. Carbon dioxide molecules simultaneously diffuse from the blood and are transported out of the lungs during exhalation.

Typical respiratory gas analysis applications include;

  • Metabolic studies
  • Whole body plethysmography
  • Pulmonary function testing
  • Spirometry

Method:

The ADInstruments Gas Analyzer in conjunction with a PowerLab data acquisition system can be used to measure and display concentrations of O2 and CO2 in real-time. The response time of the Gas Analyzer’s transducers offers accurate respiratory gas analysis from humans. The instrument features a sampling flow control, making it also suitable for use in animal studies. Note: The Gas Analyzer is only suitable for measuring gas concentrations in air and not in liquids.

Gas Analyzer
The Gas Analyzer is easy to use with no complex controls, just a simple on/off pump switch, a gas sampling port and a knob to vary the gas sampling rate (approximately 35 to 200 ml/min). Gas samples are drawn into the unit through Nafion tubing attached to an external filter on the input port (see below for more information). The oxygen sensor uses visible spectrum absorption technology and the carbon dioxide sensor uses optical infrared technology. Two analog signal outputs (BNC connections) are located at the rear of the unit to provide the corresponding voltage outputs from the O2 and CO2 analyzers.

Calibrating the Gas Analyzer
When connected to a PowerLab data acquisition system via the I2C cable, the Gas Analyzer is automatically recognized by LabChart and the factory specifications/units of the CO2 and O2 transducers are automatically entered. It is recommended that the unit is calibrated before and after each experiment with known gases.

If the Gas Analyzer is not connected to the PowerLab using the I2C cable or if it is used as a stand-alone unit with a third party analog recorder, then the CO2 and O2 outputs must be calibrated. Note: NEVER attach a high pressure gas source (i.e. gas cylinder) directly to the sampling inlet of the Gas Analyzer when calibrating.

Gas Mixing Chamber
For metabolic studies, the Gas Analyzer should be used with a Gas Mixing Chamber to ensure adequate mixing of the expired breath prior to sampling. All of the required hardware and software for these types of experiments are included in the Exercise Physiology System. Note: The Gas Analyzer is not suitable for breath-by-breath measurements in humans.

Drying and Filtering of Respired Air
ADInstruments recommend the use of a Drying Tube (Nafion) in conjunction with an In-line Filter (0.45μ hydrophobic membrane) when connecting the sampling line to the sampling port of the Gas Analyzer. This filter is necessary to prevent moisture damage to the sensors as well as removing any possible damaging particulates. When performing heavy exercise studies or in very humid environments, the Gas Analyzer should also be used in conjunction with a Desiccant Cartridge to ensure accurate O2 and CO2 concentrations as well as reduce any damage to the sensors.

For related information please see the flowing application pages.

Software:

The LabChart Advantage:

(may require additional Modules and Extensions)

  • The Gas Analyzer is automatically recognized by LabChart and the factory specifications/units of the CO2 and O2 transducers are automatically entered
  • Transfer or copy/paste data easily to word processing or spreadsheet programs for further analysis and publication-quality reports
  • Annotate data files with Comments about experimental conditions
  • The Metabolic Module (Win or Mac) for LabChart calculates and displays ventilatory parameters such as VCO2, VO2, VE and RER online from measurements of %O2, %CO2 and air flow
  • The Spirometry Extension (Win or Mac) for LabChart calculates tidal volume, minute ventilation, PIF, PEF, respiratory rate, FVC, FEV1 and can construct flow-volume loops online or offline (also see Respiratory Airflow application pages)

LabChart

LabChart software (for Windows and Macintosh) combines the familiar simplicity of a traditional strip chart recorder with the powerful analysis features of a digital acquisition system. LabChart software and a PowerLab data acquisition unit provide data integrity, easy selection of hardware settings, powerful online and offline analysis, procedure automation, seamless extraction of experimental data and flexible display options. Acquisition and analysis capabilities can be further increased with LabChart Extensions and LabChart Modules. LabChart Modules are available as part of LabChart Pro and LabChart Extensions are free for download from the website for existing LabChart users.

Metabolic Module

The Metabolic Module (Windows and Macintosh) in combination with ADInstruments hardware is ideal in the determination of cardiorespiratory function and exercise physiology measurements. Typical applications include:

  • Metabolic measurements
  • Respiratory gas analysis
  • Student exercise testing
  • Pulmonary function analysis
  • Indirect calorimetry
  • Anaerobic threshold
  • Biopotential measurements and spirometry.

The Metabolic Module records CO2 and O2 concentrations sampled from a gas mixing chamber and interprets these values in real time to provide parameters such as: VCO2/min, VO2/min, VE/min and RER. The Module also provides options for setting subject details, recording parameters and environmental conditions that includes:

  • Hardware preferences: choice of the PowerLab and associated hardware
  • Subject details: name, age, weight, height, gender, id number, comments
  • Calibration preferences: settings for automated first and second gas calibrations
  • General preferences: Averaging time (data logging) and recording time (duration of experiment) settings
  • Environment settings: Expired/inspired, atmospheric and air conditions

Spirometry Extension

The Spirometry Extension for LabChart is available on both Windows and Macintosh platforms and provides:

  • Automated calibration of respiratory flow and volume recordings
  • Advanced analysis functions
  • Generation of flow-volume plots
  • Calculation of tidal volume and respiratory rate
  • Calculation of minute ventilation, peak inspiratory and expiratory flow

GLP and 21 CFR Part 11

For those researchers working within a laboratory requiring GLP and 21 CFR Part 11 compliance the GLP Client and GLP Server are available for use with LabChart (Windows only) and PowerLab data acquisition systems. For more information, visit the Good Laboratory Practice application page or contact your nearest ADInstruments representative.

Hardware:

PowerLab Data Acquisition Systems

The PowerLab is a high-performance data acquisition unit capable of recording at speeds of up to 400,000 samples per second continuously to disk (aggregate). PowerLab units are compatible with instruments, signal conditioners and transducers supplied by ADInstruments, as well as many other third-party companies. In addition to standard single-ended BNC inputs, 4 differential Pod ports are also available for direct connection of Pod signal conditioners and appropriate transducers. Research PowerLab units include:

Systems

The PL3508B80 Exercise Physiology System is a complete physiology recording system for monitoring cardiorespiratory and metabolic function during exercise. The system records and displays continuous real-time measurements of metabolic parameters such as CO2 and O2 concentrations, airflow, air temperature, ECG or EMG.

The Exercise Physiology System includes:

Instruments

The ML206 Gas Analyzer can be used for the measurement of respiratory gas concentrations from small animals, such as rats, through to humans. It contains an infrared carbon dioxide sensor and optical oxygen detector fed from a damped microvacuum sampling pump.

Signal Conditioners

The FE141 Spirometer is a precision differential pressure transducer that is used with a PowerLab for measurements of respiratory flow rates in humans and animals. Using a flow head of a suitable size, respiratory flow rates from a variety of species can be measured.

The ML311 Spirometer Pod also measures respiratory flow rates in humans in conjunction with an appropriate respiratory flow head and PowerLab. The Spirometer Pod connects to any PowerLab with Pod ports (8-pin DIN inputs) or using the ML305 Pod Expander for units without Pod ports.

Transducers and Accessories

Airflow
Flow heads contain a fine wire-mesh and, in conjunction with a differential pressure transducer (such as the FE141 Spirometer and ML311 Spirometer Pod), the user can measure pressure changes across the wire-mesh which are proportional to airflow. ADInstruments provide the following range of flow heads:

Respiratory Rate

  • The MLT1132 Piezo Respiratory Belt Transducer is recommended for recording respiratory rate in humans.
  • The MLT415/A or MLT415/D Nasal Temperature Probe can be used to record respiratory rate in humans from nasal airflow measurements.
  • The MLT1010 Piezo Electric Pulse Transducer may be suitable for qualitatively recording respiratory rate in small animals.
  • For wireless measurements, the BioHarness Telemetry System (MLE1202 USA or MLE1201 EURO) can be used to measure a range of human biopotentials, including respiratory rate, wirelessly via radio frequency (Euro: 868.2 MHz and USA: 915 MHz)

Other Accessories
A variety of accessories are available from ADInstruments, including:

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D.H. Ho, W.L. Reed and W.W. Burggren, Experimental Biology, 619-628, 2011

Physiologic and biologic characteristics of three experimental models of acute lung injury in rats.
Henzler D, Hochhausen N, Chankalal R, Xu Z, Whynot SC, Slutsky AS, Zhang H., Anesthesia and Analgesia, 1139-1146, 2011

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S.J. E. Lucas, K.R. Burgess, K.N. Thomas, J Donnelly, K.C. Peebles, R.A. I. Lucas, J-L Fan, J.D. Cotter, R Basnyat and P.N. Ainslie, Journal of Physiology, 741-753, 2011

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The material on this page is provided in good faith and believed accurate at the time of writing. No responsibility will be taken, or liability accepted, for damages arising from the use of information herein. Readers are urged to check with respective manufacturers the accuracy of all product related information.

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