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Oscillometric measurements of respiratory system resistance (R rs ) in infants are usually made via the nasal pathways, which not only significantly contribute to overall R rs but also introduce marked flow (V')-dependent changes. We employed intrabreath oscillometry in casts of the upper airways constructed from head CT images of 46 infants. We examined oscillometric nasal resistance (R n ) in upper airway casts with no respiratory flow (R 0 ) and the effect of varying V' on R n by simulating tidal breathing. A characteristic nonlinear relationship was found between R n and V', exhibiting segmental linearity and a prominent breakpoint (V' bp ) after log-log transformation. V' bp was linearly related to the preceding value of end-expiratory volume acceleration (V″ eE ; on average r 2  = 0.96, P < 0.001). R n depended on V', and R at end-expiration (R eE ) showed a strong dependence on V″ eE in every cast ( r 2  = 0.994, P < 001) with considerable interindividual variability. The intercept of the linear regression of R eE versus V″ eE was found to be a close estimate of R 0 . These findings were utilized in reanalyzed R rs data acquired in vivo in a small group of infants ( n = 15). Using a graphical method to estimate R 0 from R eE , we found a relative contribution of V'-dependent nonlinearity to total resistance of up to 33%. In conclusion, we propose a method for correcting the acceleration-dependent nonlinearity error in R eE . This correction can be adapted to estimate R 0 from a single intrabreath oscillometric measurement, which would reduce the masking effects of the upper airways on the changes in the intrathoracic resistance. NEW & NOTEWORTHY Oscillometric measurements of respiratory system resistance (R rs ) in infants are usually made via the nasal pathways, which not only significantly contribute to overall R rs but also introduce marked flow acceleration-dependent distortions. Here, we propose a method for correcting flow acceleration-dependent nonlinearity error based on in vitro measurements in 3D-printed upper airway casts of infants as well as in vivo measurements. This correction can be adapted to estimate R rs from a single intrabreath oscillometric measurement.

Background and Objective: Selecting 'healthy' preschool-aged children for reference ranges may not be straightforward. Relaxing inclusion criteria for normative data does not affect spirometry z-scores. We therefore investigated the effect of similarly relaxing inclusion criteria in preschoolers on reference ranges for respiratory impedance (Zrs) using a modified forced oscillation technique (FOT)., Methods: The International Study of Asthma and Allergies in Childhood questionnaire classified 585 children into a healthy and five mutually exclusive groups. Zrs was measured between 4 and 26 Hz and resistance (R) and compliance (C) obtained by model fitting. Prediction models were determined using mixed effect models and z-scores compared between healthy children and the five groups., Results: Zrs data were obtained for 494 participants (4.30 ± 0.7 years) on 587 occasions. Comparison of the Zrs z-scores between the healthy children and the health groups found significant differences in children with asthma, current wheeze and respiratory symptoms, but not in children born preterm or with early-life wheeze. Adding these two groups to the healthy dataset had no significant effect on the distribution of z-scores and increased the size of the dataset by 22.3%., Conclusion: Our data suggest that preschool-aged children born preterm or with early-life wheeze can be included in FOT reference equations, while those with asthma, current wheeze and respiratory symptoms within 4 weeks of testing should be excluded. This more inclusive approach results in more robust FOT reference ranges., (© 2017 Asian Pacific Society of Respirology.)

Basal airway smooth muscle (ASM) tone has not been demonstrated in mice in vivo. To determine whether basal ASM tone is present in mouse airways we measured respiratory system impedance (Zrs) before and after either atropine or bilateral vagotomy. Zrs was measured using forced oscillations delivered via a wave-tube during slow ( approximately 35s) inflation-deflation maneuvers between transrespiratory pressures (Prs) of 0 and 20 cm H2O. A constant-phase tissue model was applied to the Zrs to calculate airway resistance (R aw), tissue damping (G) and elastance (H). Thoracic gas volume (TGV) was determined plethysmographically at Prs=0 cm H2O and by integration of the inspiratory flow. The relationship between conductance (G aw=1/R aw) and TGV during inflation was also examined. Neither atropine nor vagotomy produced any change in R aw, H, eta (=G/H), TGV or the slope of G aw vs. TGV that was different to that observed in the relevant control groups. These data show that BALB/c mice do not have cholinergic ASM tone in vivo.

We measured respiratory input impedance (1-25 Hz) in mice and obtained parameters for airway and tissue mechanics by model fitting. Lung volume was varied by inflating to airway opening pressure (Pao) between 0 and 20 cm H2O. The expected pattern of changes in respiratory mechanics with increasing lung volume was seen: a progressive fall in airway resistance and increases in the coefficients of tissue damping and elastance. A surprising pattern was seen in hysteresivity (eta), with a plateau at low lung volumes (Pao < 10 cm H2O), a sharp fall occurring between 10 and 15 cm H2O, and eta approaching a second (lower) plateau at higher lung volumes. Studies designed to elucidate the mechanism(s) behind this behavior revealed that this was not due to chest wall properties, differences in volume history at low lung volume, time dependence of volume recruitment, or surface-acting forces. Our data are consistent with the notion that at low lung volumes the mechanics of the tissue matrix determine eta, whereas at high lung volumes the properties of individual fibers (collagen) become more important.