Reference values for respiratory impedance measured by the forced oscillation technique in adult men and women.

INTRODUCTION: The forced oscillation technique (FOT) is a particularly useful test of the mechanical properties of the respiratory system that has an increasingly important role in lung function laboratories. There is general agreement in the literature that the determination of reference values is of utmost importance in the clinical use of the FOT.

OBJECTIVE: Our aim was to present reference values for whole-breath FOT measurements, establish which anthropometric variables were more predictive of impedance parameters, and provide all the details to adequately adopt these reference equations in individual laboratories.

METHODS: We prospectively evaluated a randomly selected non-smoking sample of the adult Brazilian population (288 subjects, 144 males and 144 females aged 20-86 years). The volunteers were separated by sex and divided into six groups based on decade of age. Sex-specific linear prediction equations were developed by multiple regression analysis using age, body mass and height as explanatory variables.

RESULTS: Age introduced a slight, but significant, reduction of resistance in men (P < .001) and women (P < .001). In general, significantly higher values of resistance were observed in females (P < .0001). Among the anthropometric variables analyzed, height was the best predictor for all parameters studied.

CONCLUSION: This study provides an original frame of reference for the FOT in Brazilian males and females aged 20-86 years. Height was the best predictor of respiratory impedance parameters. Details contributing to an adequate adoption of these reference equations elsewhere by transference and verification are also provided.