Background: intra-breath analysis of oscillometry parameters is a growing research area since it increases sensitivity and specificity to specific pathologies and conditions (Kaminsky, ERJ, 2023). However, reference equations for within-breath oscillometry parameters in adults are missing.

Methods: White adults with normal spirometry, BMI<30kg/m2, without a history of smoking, respiratory symptoms, pulmonary or cardiac disease, neurological or neuromuscular disorders, and respiratory tract infections in the previous 4 weeks were eligible for the study. Study subjects underwent oscillometry (multifrequency waveform at 5-11-19 Hz, Resmon PRO FULL, Restech Srl, Italy) according to international standards in 5 centers in Europe and the USA. The within-breath and total resistance (R) and reactance (X), the resonance frequency, the area under the X curve, and the frequency dependence of R were submitted to Lambda-Mu-Sigma (LMS) models (a special case of the GAMLSS models) for deriving reference equations. For each output parameter, an AIC-based stepwise input variable selection procedure was applied.

Results: 144 subjects (age 20.8 ? 86.3 years; height 146 ? 193 cm; BMI 17.42 ? 29.98 kg/m2; 56% females) were included. We derived reference equations for 29 oscillatory parameters. Equations for intra-breath parameters at 5Hz are reported in Figure.

Conclusion: Reference equations for within?breath parameters are available for the first time.