Smoking is the main risk factor for COPD. Oscillometry is a easy to perform, not time-consuming technique with low patient burden that provides detailed assessment of respiratory impedance (Z) measurement. The study aims were to evaluate Z as a means to detect early airway abnormalities in past smokers (PS) and active smokers (AS) compared to non-smokers (NS). Methods: We included 7560 subjects (Age 18-82) of the Austrian LEAD general population cohort, a longitudinal single-centered, observational study. Z-measurements were obtained (Resmon Pro Full, Restech, Italy) as conducted by trained technicians. Resistance (R) and reactance (X) at 5 Hz were analysed as well as the area under X (AX) and frequency dependence of R (R5-R19). Data are reported as % of predicted (Berger et al., ERJ open 2021). Smokers were subdivided by the number of pack years (PY). Results: AS with > 10 PY had higher R5 values than NS and PS< 10 PY groups. In addition, this group has manifested higher AX than PS >10 PY. PS, irrespective of the number of PY, showed no Z differences compared to the NS (Table). * p<0.05 vs Smoker > 10 pack/years. Data are presented as median (IQR). Conclusion: Oscillometry is a feasible approach to identify Z changes in active smokers.

Small airway dysfunction (SAD) is a clinically important problem in asthmatics. Impedance (Z) measurement by oscillometry is considered a reliable, easy to perform and quick technique to determine SAD. Limited data are available about the presence of SAD in subjects with past history of asthma/asthmatic bronchitis. The aim of the current study is to assess SAD with Z in past (PA) and current asthmatics (CA). Methods: We included 7219 subjects aged 18-82 years from the Austrian LEAD study, a longitidinal population-based cohort study. Based on questionnaire data, we identified:(1) healthy participants without respiratory pathologies and symptoms (N=6559), (2) subjects reporting past diagnosis of asthma (N=315) and (3) subjects with current asthma (N=345). Resistance (R5) and Reactance (X5) at 5 Hz, the area under X (AX), and the frequency dependence of R (R5-R19) were analyzed. Results * p<0.05 with healthy. ° p<0.05 with Past asthma. % predicted according to Berger et al. (2021). Data are presented as median (IQR). Subjects with current asthma when compared to healthy subjects presented oscillometry parameters compatible with SAD. Subjects with past asthma presented with higher R5. Conclusion: Our population-based data confirm the presence of Z changes, indicative of SAD in current asthmatics. Oscillometry may identify SAD in asthmatics and sharpen therapy management.

Background The forced oscillation technique (FOT) is ideally suited to diagnose and manage respiratory diseases and requires only minimal patient cooperation. The present study aimed to create sex-specific reference equations for children and adolescents aged 6 to 17 years. Methods 981 healthy participants aged 6 to 17 years of the Austrian LEAD general population cohort were included. Nearly all participants had normal weight (BMI ≤ 99th percentile) and all had normal lung volumes (total lung capacity (TLC) ≥ lower limit of normal). FOT data were collected with the Resmon Pro FULL device using a single frequency mode of 8 Hz. Sex-specific prediction equations were developed for Resistance (R) 8 Hz (8) expiratory (exp.), R8 inspiratory (insp.), R8 total (tot.), Reactance (X) 8 exp., X8 insp. and X8 tot. using the LMS (lambda, mu, sigma) method. Since body height showed the most significant influence on the parameters chosen, we used it as a single covariate. Results We created percentile curves and look up tables including reference values for a height from 101 to 183 cm. Male and female children showed a progressive decline in R values over the height spectrum studied. Similarily, X values progressively increases with higher height. R values are higher in females than in males. Conclusion Our study provides highly accurate reference values for clinically useful respiratory impedance (Zrs) parameters in the form of look up tables. To the best of our knowledge, our cohort is the largest population in the age of 6 to 17 years studied so far concerning Zrs. Further studies have to link these height related geometric changes of the airway tree to related changes in lung size.

Background Determination of reference values of respiratory impedance (Zrs) measured by forced oscillation technique (FOT) is of utmost importance in its clinical use. The aim of our study was to present reference values for whole-breath FOT measurements for adults (18-80 years). Methods 1264 adult healthy asymptomatic never-smokers of the Austrian LEAD Study cohort were included in the analysis. Nearly all participants had normal weight (BMI ≤ 35) and had normal lung volumes (total lung capacity (TLC) ≥ lower limit of normal). Data were collected with the Resmon Pro FULL device using a multiple frequency mode of 5-11-19 Hz. Sex-specific prediction equations were developed for Resistance (R) 5 Hz (5) expiratory (exp.), R5 inspiratory (insp.), R5 total (tot.), Reactance (X) 5 exp., X5 insp. and X5 tot. using the LMS (lambda, mu, sigma) method. Body height only showed a significant influence on the parameters chosen. Therefore, it was used as a single covariate. Results We created percentile curves and look up tables including reference values for a height from 143cm to 204cm. While R values in men decrease with height between 150cm and 180cm and flattened at higher length (>180cm), R values in females progressively declined with higher height. X showed a progressive increase with height in men and a flattening of X at higher length (>180cm) in women. Conclusion Our study provides highly accurate reference values for clinically useful Zrs parameters in the form of look up tables. Beside the establishment of reference values further research is required for the optimal positioning of Zrs in respiratory diagnostics.

Despite being the golden standard to diagnose and classify airway diseases, the sensitivity of spirometry to detect early airway impairment can be questioned (Wouters et al, JCM 2021). The current study aims to investigate the association between abnormal oscillometry values and the presence of respiratory symptoms in subjects with normal spirometry. 5646 adults (18-90 years) from the Austrian LEAD general population cohort with normal spirometry (FEV1/FVC and FVC) were included. For each subject, within-breath oscillometry (RESMON PRO FULL, RESTECH Srl, Italy), spirometry, respiratory symptoms, and/or respiratory diseases were recorded on the same day. Abnormal FOT was defined according to Oostveen et al., ERJ 2013. We computed the risk ratios of presenting symptoms and/or diseases for subjects with 1) an abnormal oscillometry parameter (n=785), 2) abnormal resistance (Rrs; n=541), 3) abnormal reactance (Xrs; n=481)), 4) abnormal inspiratory parameters (n=351), and 5) abnormal expiratory parameters (n=667). Changes in FOT parameters are highly prevalent in subjects with normal spirometry and are consistently related to reported respiratory symptoms and past or present respiratory diseases (Figure). FOT is a simple, feasible and sensitive method to objectify respiratory conditions in normal spirometry.

Oscillatory reactance (Xrs) is markedly dependent by the frequency of the oscillatory pressure. The frequency at which Xrs crosses zero is called resonant frequency(Fres) and the area of the reactance spectrum from the lowest stimulating frequency to Fres is indicated as Area of Reactance(Ax). Despite their use to investigate peripheral lung mechanics and for the evaluation of bronchial reversibility tests (King et al. ERJ 2020), no data exists about their dependence on stimulating waveforms. We studied the effects of different stimulating waveforms on the derivation of Ax and Fres using 2 stimuli: a pseudorandom signal containing prime numbers from 5 to 37 Hz and a multi-frequency waveform containing only 5,11, and 19 Hz components. In total, 36 asthmatic children (6.4-12.9 yrs; 112-174 cm) were measured using the 2 different waveforms in random order with a commercial oscillometry device (RESMON PRO FULL, RESTECH, Italy). Measurements were performed in triplicate and repeated after the administration of bronchodilator. Pooled data PRE and Post-BD were compared using the Bland-Altman method and differences evaluated against published values of short-term variability. Using the 2 examined waveforms did not introduce any significant bias and observed differences were consistent with expected short-term variability supporting the equivalence of the 2 waveforms for the derivation of Ax and Fres.

Aim: Oscillometry, or forced oscillation technique (FOT), measures respiratory mechanics during quiet breathing. Available devices are designed for ambulatory use and are too cumbersome and expensive for wider applications. We aimed at evaluating in-vitro the accuracy of a novel small handheld FOT device that uses a miniaturized fan for generating the FOT forcing waveform. Methods: Two mesh-type resistors of 5 and 15cmH2O*s/l were used to simulate airway resistance (Rrs) and three glass bottles of 3, 5, and 15 l were used to provide a reactance (Xrs) of approximately -10.5,-6.9 and -2.3 cmH2O*s/l, respectively. Different combinations of these loads were assembled and connected to a servo-controlled piston for the simulation of spontaneous breathing patterns. This active test lung was measured using a pseudo-random noise with 5-11-19Hz by both the handheld (FOT HH, RESTECH SRL, Milano, Italy) and an in-house loudspeaker-based oscillometry device used as gold standard(FOT REF). Each combination of loads was measured with two different breathing patterns (1: Vt 0.4 l, RR 17bpm, Ti 1.60s; 2: Vt 0.28 l, RR=23.5, Ti 1.19s). Results: Rrs and Xrs from the handheld device are in close agreement with those provided by the reference system and do not show any relevant bias (see figure). Conclusion: The fan-based approach provides accurate multi-frequency measurements and has the potential for deployment on large-scale and in-field applications.