Reactance and elastance as measures of small airways response to bronchodilator in asthma

Abstract

Bronchodilation alters both respiratory system resistance (Rrs) and reactance (Xrs) in asthma, but how changes in Rrs and Xrs compare, and respond differently in health and asthma, in reflecting the contributions from the large and small airways has not been assessed. We assessed reversibility using spirometry and oscillometry in healthy and asthma subjects. Using a multibranch airway-tree model with the mechanics of upper airway shunt, we compared the effects of airway dilation and small airways recruitment to explain the changes in Rrs and Xrs. Bronchodilator decreased Rrs by 23.0 (19.0)% in 18 asthma subjects and by 13.5 (19.5)% in 18 healthy subjects. Estimated respiratory system elastance (Ers) decreased by 23.2 (21.4)% in asthma, with no significant decrease in healthy subjects. With the use of the model, airway recruitment of 15% across a generation of the small airways could explain the changes in Ers in asthma with no recruitment in healthy subjects. In asthma, recruitment accounted for 40% of the changes in Rrs, with the remaining explained by airway dilation of 6.8% attributable largely to the central airways. Interestingly, the same dilation magnitude explained the changes in Rrs in healthy subjects. Shunt only affected Rrs of the model. Ers was unaltered in health and unaffected by shunt in both groups. In asthma, Ers changed comparably to Rrs and could be attributed to small airways, while the change in Rrs was split between large and small airways. This implies that in asthma Ers sensed through Xrs may be a more effective measure of small airways obstruction and recruitment than Rrs. NEW & NOTEWORTHY This is the first study to quantify to relative contributions of small and large airways to bronchodilator response in healthy subjects and patients with asthma. The response of the central airways to bronchodilator was similar in magnitude in both study groups, whereas the response of the small airways was significant among patients with asthma. These results suggest that low-frequency reactance and derived elastance are both sensitive measures of small airway function in asthma.

Combined forced oscillation and fractional-order modeling in patients with work-related asthma: a case–control study analyzing respiratory biomechanics and diagnostic accuracy

“…4 e). This finding is consistent with the work of Bhatawadekar et al [ 38 ], which used a single compartment model fit to estimate Ers (1/Crs). These authors pointed out that Ers is associated with small airways, and potentially a very clinically useful measure in asthma.…”

Combined forced oscillation and fractional-order modeling in patients with work-related asthma: a case-control study analyzing respiratory biomechanics and diagnostic accuracy

“…Both results are in close agreement with the spirometric and plethysmographic changes observed after BD use in the present study (Table 2), which described changes associated mainly to central airways. These results are in line with the recent work of Bhatawadekar and collaborators [40] investigating the bronchodilator response in asthma. Thus FrOr parameters were not the most adequate to diagnose these changes because these parameters are more related to peripheral airways, while the observed BD responses are involved with more central airways.…”

“…WRA introduced a decrease in C ( Figure 4E). This finding is consistent with the work of Bhatawadekar and collaborators [40], which used a single compartment model fit to estimate Ers (1/Crs). These authors pointed out that Ers is associated with small airways, and potentially a very clinically useful measure in asthma.…”

Combined forced oscillation and fractional-order modeling in patients with work-related asthma: a case-control study analyzing respiratory biomechanics and diagnostic accuracy

“…WRA introduced a decrease in C ( Figure 4E). This nding is consistent with the work of Bhatawadekar and collaborators [40], which used a single compartment model t to estimate Ers (1/Crs). These authors pointed out that Ers is associated with small airways, and potentially a very clinically useful measure in asthma.…”