Background: Asthma attacks result in more than 70,000 hospital admissions every year in the UK. Spirometry is effort dependent and difficult for patients to perform when they feel unwell. Forced Oscillation Technique (FOT) evaluates respiratory impedance during normal tidal breathing, and the feasibility and utility of measuring resistance (R) and reactance (X) during asthma attacks in adults have not been explored.
Methods: This is an observational study with patients hospitalised following an asthma attack. Patients performed lung function tests (spirometry, FOT, and FeNO) within 24h of the admission.
Results: Forty-eight patients have been recruited to date; 8 of them could not perform spirometry and 2 could not perform FOT. Of the remaining 38 most were female (65.8%) with median age 42. The median of lung function parameters were FEV1 2.2L, 69%pred; FVC 2.9, 78%pred; FEV1/FVC 0.71; FEF25-75% 1.46, 43%pred; R5exp 5.14cmH20.s/L; R20 3.9cmH20.s/L; R5-20 0.94cmH20.s/L; X5ins -2.56cmH20.s/L; X5exp -1.65cmH20.s/L; AX 16.24cmH2O.s/L, and FeNO 19ppb. FOT and spirometry parameters showed highly significant moderate to strong correlations. R5exp showed correlation with FEV1, FVC as well as with FEF25-75%(rho=-0.58,-0.55,-0.52, respectively). Additionally, stronger correlations were observed between X5exp and FEV1, and FEF25-75% (Rho=0.68 and 0.73, respectively); X5ins and FVC (rho=0.65), as well as between R5-20 and FEF25-75%(rho=-0.60).
Conclusions: Patients hospitalised following an asthma attack tolerate FOT better than spirometry and the 2 tests showed moderate to strong correlation of parameters. Therefore, FOT can be useful evidence of airways impairment in hospitalised asthma patients.