Reference values for within-breath pulmonary impedance parameters in asymptomatic elderly

A new application for the forced oscillation technique (FOT) has been described by Dellaca et al. using sinusoidal pressure variations at 5 Hz to detect expiratory flow limitation by measuring the within-breath reactance [termed difference between inspiratory and expiratory X5 (DX5)]. Few studies have been performed on respiratory phase differences in the elderly.

Our aim was to present reference values for within-breath impedance measurements and to examine how the earlier mentioned method performs in a study population of asymptomatic elderly.

An age- and sex-stratified random sample was drawn from the elderly population of Bergen, Norway. Among the healthy non-smoking responders from a postal questionnaire study, 148 were selected to perform FOT measurements using an impulse oscillometry system (IOS). Seventy five of these participants had a normal spirometry and were able to perform at least two valid FOT measurements. Predictive equations for men and women were created for FOT parameters by linear multiple regression analysis. DX5 was calculated from the within-breath variation of reactance at 5 Hz.

This study presents reference values for whole-breath and within-breath impedance parameters in asymptomatic elderly aged >70 years using the IOS method. We found higher resistance measurements than what is reported in previous studies and significantly larger frequency dependence.