TEMPERATURE STANDARDIZATION OF MULTIPLE SPIROMETERS

In respiratory health surveys involving multiple spirometers, spiromet er differences may introduce important biases, We investigated tempera ture measurement variability as a cause of spirometer differences. Dig ital thermometers recorded internal (cylinder) and external (outer cas ing) temperatures of six similar rolling-seal spirometers during field use and in laboratory tests at controlled room temperatures. Internal and external thermometers substantially agreed in recording spiromete r temperature changes, which lagged room temperature changes. Offsets of individual thermometers from overall mean readings were roughly the same in field testing of 3908 students in > 60 schools over 5 months and in subsequently laboratory tests, Thermometers differed by as much as 1.3 degrees C, causing differences as large as 0.8 % in vital capa city measurements. We conclude that (1) interior and exterior temperat ures official rolling-seal spirometers do not differ greatly, although both may differ from surrounding air temperature; and (2) variations between individual digital thermometers may be large enough to bias sp irometer data appreciably in large-seal surveys. Variations should be controlled by selection of similar-reading thermometers and/or correct ion to a uniform standard.