A COMPARISON OF METHODS OF CALIBRATING THE PNEUMOTACHOGRAPH

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Abstract
A comparison has been made between methods of calibrating the pneumotachograph and a study made of the effects of altering the composition and temperature of the gas passing through the instrument. The sources of error in the various methods have been examined. A Fleisch pneumotachograph head was used. As this instrument is a type of viscous flowmeter, variations in the viscosity of the gas passing through the instrument will affect the readings obtained. The Wright Respirometer is flow-sensitive and not suitable for calibrating the more accurate pneumotachograph. A Rotameter or spirometer may be used with an accuracy of approximately 2 per cent. A hand-driven syringe has been found to result in an accuracy of better than 0.5 per cent, and was also simple to use for routine calibration. Alterations in the viscosity of the gas, by change in either composition or temperature, change the response of the instrument in a manner that agrees with theoretical calculations. As the apparatus has an accurate response to gas flow rates, it is suggested that best results may be obtained from measuring respiratory volumes if a computer is supplied with information simultaneously from a mass spectrometer and a temperature-sensing device.

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