Respiratory Gas Analysis

In mammalian physiology, respiration can be summarized as the transport of oxygen from the clean air (abundant with oxygen) to the tissue cells and the transport of carbon dioxide in the opposite direction. In contrast to the biochemical definition of respiration at the individual cells, this process only involves the bulk flow and transport of metabolites between the organism and external environment.

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 into and out of the body. Each inhalation transports clean oxygenated air into the lungs, where molecules of oxygen diffuse into the blood from the gaseous environment. Carbon dioxide diffuse simultaneously from the blood into the gaseous environment, which is transported out the lungs during exhalation.

The ADInstruments Gas Analyzer is suitable for analyzing O₂ and CO₂ concentrations and recording these using a PowerLab data acquisition system. It is only suitable for measuring gas concentrations in air and is NOT suitable for liquids.

The analyzer is easy to use with no complex controls, just a simple pump on/off switch, a gas sampling port and a knob to vary the gas sampling rate (approximately 35 to 200 ml/min). The sensors are state of the art with the oxygen system using visible spectrum absorption and the carbon dioxide using 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.

Applications
The Gas Analyzer is suitable for a range of applications including

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

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. 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 (0.45 micron 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 analyzers as well as removing any possible damaging particulates.The Gas Analyzer should also be used in conjunction with a Desiccant Cartridge when performing heavy exercise studies or in very humid environments to ensure accurate O₂ and CO₂ concentrations as well as reduce any damage to the analyzers due to fluid.

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.

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. NEVER attach a high pressure gas source (i.e. gas cylinder) directly to the sampling inlet of the Gas Analyzer when calibrating.

Note: For related information please see the flowing application pages.

• Spirometry/Respiratory Airflow application page for flow and volume measurements
• Oximetry application page for non-invasive arterial oxygen saturation measurements

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.

Respiratory rate can be calculated online or offline using the Cyclic Measurements (Win) or Computed Input/Cycle Variables (Mac) features in LabChart.

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

Metabolic Module (Windows or Macintosh)
The MLS240/6 Metabolic Module for LabChart 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/8M or other “Custom” 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

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.

ADInstruments provide a range of data acquisition systems, signal conditioners, respiratory flow heads, pressure transducers and amplifiers that connect to PowerLab data acquisition systems for monitoring air flow and calculating respiratory data.

PowerLab Data Acquisition Systems
The PowerLab is a high-performance data acquisition unit suitable for a wide range of research applications. Typical applications include human and animal physiology, pharmacology, neurophysiology, biology, zoology, biochemistry, and biomedical engineering. Units are capable of recording at speeds of up to 400 000 samples per second continuously to disk (aggregate), and are compatible with instruments, signal conditioners and transducers supplied by ADInstruments, as well as many other brands. 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. These systems include:

• ML866 PowerLab 4/30 - 4 Channels
  
• ML870 PowerLab 8/30 – 8 Channels
• ML880 PowerLab 16/30 – 16 Channels

System and Instruments
ML870B80 Exercise Physiology System
This 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:

• ML870 PowerLab 8/30 (LabChart and Scope software)
• MLS260 LabChart Pro software
• ML132 Bio Amp
• ML206 Gas Analyzer
• MLA246 Gas Mixing Chamber
• ML141 Spirometer
• ML309 Thermistor Pod
• MLA240 Exercise Physiology Accessory Kit

ML206 Gas Analyzer
The 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.

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

• MLA6024 Desiccant Cartridge
• MLA0343 Drying Tube (Nafion)
• MLA6024 Desiccant Cartridge
• MLA0110 In-line Filters (10 Pack)
• MLA304 Disposable Filters, Supplied in packs of 50
• MLA1008 Nose Clips, Supplied in packs of 50
• MLA1026 Reusable Mouthpieces (10)
• MLA1011A Clean-bore Tubing & Tubing Adapter
• MLA1013 Tubing Adapter (35mm ID)
• MLA1029 Face Mask Kit (adult small and medium)
• MLA1028 Face Mask (adult medium)
• SP0141 Adult Face Mask (small)
• MLA5530 Calibration Syringe

Note: the MLT1132 Respiratory Belt or MLT415/D Nasal Airflow Temperature Probe can be used to monitor respiratory rate

Ventilatory sensitivity to mild asphyxia: prone versus supine sleep position

B C Galland, D P G Bolton, B J Taylor, R M Sayers and S M Williams, Archives of Disease in Childhood, 423-428, 2000

In infants respiratory patterns were measured by inductive plethysmography (Respitrace model 150; Respitrace Co., New York, USA), a technique proposed which considers that the respiratory system moves with two degrees of freedom of motion; the sum of the displacement detected by bands placed around the ribcage and abdomen equals tidal volume measured at the mouth. In studies of infants and children, there is good correlation between Respitrace sum and tidal volume so long as the studies are short term and in the controlled laboratory setting. Heart rate and arterial oxygen saturation (Sao2) were measured from the pulse oximeter (Nellcor N-200, Nellcor Hayward, California, USA)……... The percentage of inspired 02 and CO2 was measured from a Datex gas analyser (Normocorp 200-oxy CO2-O2 Datex Instumentarium Corp., Helsinki, Finland). The signals from the pulse oximeter, Respitrace and Datex wererelayed through the integrated hardware/software system of the MacLab (Adinstruments Pth Ltd, Australia).

Lack of integrative control of heat production and heat loss after capsaicin administration.

Toshimasa Osaka, Akiko Kobayashi, Tai Hee Lee, Yoshio Namba, Shuji Inoue, and Shuichi Kimura, Pflugers Archiv European Journal of Physiology, 440-445, 2000

The methods for recording O2 consumption and colonin and tail temperature were similar to those descibeded previously: Toshimasa Osaka et al, NeuroReport, 11, 2425-2428, 2000. Colonic temperature was measured with a thermistor probe inserted approx. 60 mm into the anus. Tail skin temperature was measured with a small thermistor which was taped to the dorsal surface of the of the rat’s tail, to assess vasoactive changes indirectly. The intermittent expiratory gas from the artificial respirator was introduced into a 30 mL reservoir which was continuously ventilated at 100 mL/min. The difference in O2 concentration between ambient and reservoir air was measured with an O2 analyser (LC700E, Toray, Japan). All signals were monitored with a PowerLab for on-line data display, storage, and analysis.