Lung volumes and ventilatory flows: report of Working Party.

In § 3.5.1.6. the authors emphasize the importance of adequate temperature measurement in the spirometer. However, temperature stability is also important. When a patient breathes in a spirometer, heat is dissipated due to various sources, the heat of reaction in the CO2-absorber being the most important. The resulting increase in temperature is counteracted by the heat capacity of the instrument and by natural heat transfer to the ambient air, and is, therefore, dependent on the construction of the instrument and the materials used. Consequently, the spirometer volume increases, and this may lead to substantial errors in FRC-determinations, since it would lead to undetected imperfect oxygen supply, and incorrect helium meter readings. This effect is very prominent when dry rolling seal spirometers are used for FRC-measurements. Does the Working Party have a recommendation regarding temperature stability?