Effects of temperature on Vitalograph spirometer readings.

Abstract

ABsTRAcr Spirometric variables were obtained from nine symptomless subjects, who performed forced expiratory manoeuvres with three Vitalograph spirometers at three different ambient temperatures (36.5°C, 24-10C, and -7.3°C) Hutchinson noticed when using his spirometer that subjects had larger vital capacities in summer than winter and therefore decided to correct for the effects of changes in ambient temperature.' He chose to correct for all volumes to 60°F (15°C), which was apparently an average indoor temperature in London at that time. Because of this observation it has become accepted practice to convert volumes from the temperature and pressure around the recording equipment to a standard condition, which for most purposes is that obtaining in the lung.2 Because we were engaged in epidemiological surveys using the Vitalograph spirometer in different ambient conditions we wondered whether this practice was valid. We have therefore studied the effects of temperature on Vitalograph spirometer readings.

Standardisation of spirometry

“…In situations where the ambient air temperature is changing rapidly (.3˚C in ,30 min), continuous temperature corrections may be necessary. Spirometer users should be aware of potential problems with testing performed at lower ambient temperatures: 17˚C is the lower limit [55][56][57][58][59][60][61][62][63] for ambient temperature, unless a manufacturer states that their spirometer will operate accurately at lower ambient temperatures. If barometric pressure is not used in calculating the BTPS correction factor, the range of barometric pressures over which the BTPS correction factor is valid must be published by the manufacturer.…”

“…The rationale for this recommendation is based, in part, on the problems with finite cooling times of gases in volume-type spirometers [55][56][57] and the problems of estimating BTPS correction factors for flow devices [58][59][60]. When a subject performs an FVC manoeuvre, the air leaving the lungs is ,33-35˚C [61,62] and saturated with water vapour.…”

Lung volumes and forced ventilatory flows

“…In a water-seal spirometer the water temperature can be used for correcting inspiratory and expiratory gas volumes. In spirometers equipped with a gas circulation pump the gas temperature at the outlet of the spirometer, or under the spirometer bell, is an acceptable compromise; in spirometers with a common gas inlet and outlet the inspiratory temperature should be measured at that point; the site for expiratory temperatu.re corrections should be carefully chosen within the spirometer [106,149].…”

BTPS Correction with Dynamic Spirometers

“…Temperature measurements in the mouthpiece showed that in spite of the rapid airflow in a forced expiration, the TD between body and spirometer de creased by about 50%, a finding not ex pected by us and others [2,3,5,14,15]. Cooling proceeds rapidly in the 42-cm tube; the temperature of the expired air at the moment of recording amounted to 85-88% of the ambient temperature.…”

“…This also in volved the problem of correct volume cor rection to BTPS [1,4,12,[16][17][18]. The liter ature offers different data concerning the question how to handle temperature cor rection in these usually half-open systems [2,3,6,14,15]. The uncertainty in the answer is reflected in different types of evaluation forms, offering two scales, which so far have been used at the exam iner's discretion.…”