We read with interest the article in the June 2020 issue of CHEST from Cottee et al,1 examining 52 patients with asthma, which concluded that bronchodilator response to albuterol 400 mg using forced oscillation technique (airway oscillometry [AO]) with Thorasys Tremoflo was more sensitive than spirometry at identifying poor disease control with the asthma control test.1 This pattern was observed for reactance area (AX) and reactance at 5Hz but not for resistance at 5Hz (R5).
Intriguingly, Cottee et al1 used reference values for bronchodilator response for AO in healthy subjects, which would not equate to patients with asthma, in whom reversibility would be much greater because of alterations in resting bronchomotor tone and airway geometry. In contrast, they used reversibility criteria for spirometry derived from patients with asthma. Hence, we belive their analysis is inherently flawed. For example, in a study of 95 patients with asthma and 61 healthy volunteers using AO measured by the Jaeger Masterscreen device; the relative mean percentage change in response to albuterol 400 mg was 6% vs 2%, respectively, for FEV1 and 34% vs 15% for R5.2
Moreover, Cottee et al1 did not evaluate the frequency dependence of heterogeneity for resistance, for example, between 5 Hz and 20 Hz (R5-R20), which reflects small airways dysfunction.3 Another study in patients with asthma using the Jaeger device looking at reversibility with 5,000 mg nebulized albuterol showed mean percentage responses amounting to 46% for R5, 116% for R5-R20, 83% for AX, 32% for FEV1, and 58% for forced expiratory flow between 25% and 75% of FVC.4
We also recently reported on reversibility with albuterol 400 mg in 46 patients with asthma with the Tremoflo (Thorasys Thoracic Medical Systems Inc, Montreal) device.5 We used the Asthma Control Questionaire-6, comparing a cut point of <1.5 vs $1.5 to assess poor control. Differences were detected in mean percent reversibility for R5: 15% vs 25% (95% CI, 18 to 2; P < .05), R5-R19: 27% vs 55% (95% CI, 53 to 3; P < .05) and FEV1: 5% vs 10% (95% CI, 7 to 1; P < .05).
Using an Asthma Control Questionaire-6 cut point of <0.75 vs $0.75 to assess good control revealed differences in mean percent reversibility for R5: 11% vs 24% (95% CI, 22 to 5; P < .01) and R5-19: 18% vs 51% (95% CI, 60 to 6; P < .05), but not for AX or FEV1 (P > .05).
Hence, although we concur with Cottee et al1 that AO is a useful adjunct to spirometry in asthma, we would suggest that reversibility criteria for AO should be used in reference to asthma. Furthermore, measuring reactance as well as resistance heterogeneity should be considered together when evaluating lung function before and after albuterol.