Reference equations of the impulse oscillatory in healthy Thai adults

The ethnicity is significantly under-reported and this may limit the applicability of current impulse oscillometry (IOS) equations to heterogeneous patient populations. Establishing predictive equations for the IOS in the Thai adult population is still required. Therefore, this study aimed to establish reference equations for the IOS in the Thai adult population.

This retrospective cross-sectional study of IOS parameters in healthy adults aged greater than 20 years old with normal spirometry and who had no chronic respiratory diseases. Pre-bronchodilator (BD) IOS was performed in all subjects. Reference equations were calculated separately for men and women using multivariable linear regression analysis.

A total of 127 subjects (87 men and 40 women) with a mean age of 48.7±17.2 (range, 22-92) years were included. The resistance at 5 Hz (R5), resistance at 20 Hz (R20), and area under reactance curve between 5 Hz and resonant frequency (AX) were significantly higher in women compared to men. The reference equations of the IOS parameters were established for men and women. Age, height, and bodyweight were shown to be the influential predictor as they contributed to the most of IOS indices except for the R5-R20 in men equations. Bodyweight was shown to be the influential predictor as it contributed to the most IOS indices except for the X5 in women's equations.

We provided the reference equations for the IOS indices in Thai adults. IOS indices including R5, R20, and AX were significantly higher in women compared to men.