To establish reference values for lung function test in Filipinos, 283 (130 males and 153 females) normal non-smoking (< 0.5 pack years), adults were studied using a body plethysmograph (Jaeger, West Germany). Spirometric indices were integrated from a pneumotachograph (linear at flows between 0-20 1/sec with ± 2% error). Spirometric performance and measurements followed the ATS Snowbird Workshop recommendations. Lung volumes and airway resistance (Raw) were taken from the average of three plethysmographic determinations.

Multiple linear regressions with backward elimination was done. The data obtained was regressed against independent variables of age height, weight, and body surface area for each sex.

Analysis of variance (ANOVA) of the regression equations for most parameters were significant at = 0.01. In a few parameters were significance was = 0.05. Only in Raw was the regression model not significant. The coefficient of determination (R) of our regression equations were low (<0.50). However, such low R have been observed in other predictions equations which have gained widespread acceptance, attesting to their clinical usefulness. Ninety five percent confidence interval was used to determine the lower limit of normal for FEV1 and FVC. Since the other parameters showed greater individual variability, cumulative percentiles of % of predicted were determine instead (Knudson 1977). For performance test, the 5th percentiles of % of predicted was computed. For lung volumes, the 5th and 95th percentiles were determined. For Raw, the 95th percentiles of the actual values was used. Since there were fewer subjects above the age of 60 years, the use of these equations is subject to this limitation.