Investigation of Dynamic BTPS (Body Temperature Pressure Staturated) Correction Factors for Spirometric Data

摘要

Because it is often difficult to completely control ambient temperature, a study was conducted to investigate dynamic BTPS correction factors for spirometric data. A forced expiratory simulator system was heated to 37 degrees C and loaded with air saturated with water vapor. This air was then forced from the simulator into a dry rolling seal spirometer maintained at various ambient temperatures from 3 to 32 degrees C. Errors in FEV1 from assuming a constant BTPS correction ranged from 7.6 percent at 3 degrees to 2 percent at 23 degrees C. Errors in peak flow ranged from 14.3 percent at 3 degrees C to 4.9 percent at 23 degrees C. Differences between errors observed when saturated and dry air were forced into the spirometer indicate that water vapor condensation introduces an added heat load to the spirometer. The additional heat from water vapor condensation adds approximately one percent to the error in FEV1, particularly at lower temperatures. A model was developed to provide an estimate for a dynamic BTPS correction factor.