Cut-points for response to mannitol challenges using the forced oscillation technique

Abstract

The forced oscillation technique (FOT) can be used to determine airway hyperresponsiveness, but the cut-points for changes in respiratory system conductance (Grs) and reactance (Xrs) that define a positive mannitol challenge are not known. Furthermore, the effects of changes in lung volume on these cut-points or on the repeatability of the test are unknown. In 15 non-asthmatic and 52 asthmatic subjects, response to mannitol challenge was measured by Grs and Xrs, using FOT, and by FEV(1). The FOT variables were adjusted for inspiratory capacity (IC) at each dose. Dose response slope (DRS) was used in receiver operator characteristic (ROC) analysis to compare the ability of adjusted and unadjusted DRSGrs and DRSXrs to detect a positive challenge, defined as PD(15)FEV(1) ≤635 mg mannitol. Mannitol challenges were positive in 32 asthmatic and 2 non-asthmatic subjects. Both DRSGrs and DRSXrs detected positive challenges (p < 0.0001 for both), and this was not altered by adjustment for IC for either DRSGrs (p = 0.21) or DRSXrs (p = 0.90). FOT cut-points for a positive challenge were 27% fall in Grs or 0.93 cm H(2)O/L/s decrease in Xrs at 635 mg. Repeatability of DRSGrs (±2.01 doubling doses) and DRSXrs (±1.95dd) was comparable with DRSFEV(1) (±1.67dd) and was not improved by adjustment for IC. Grs and Xrs, measured by FOT, provide a sensitive, repeatable measure of response to mannitol challenge. Adjusting for lung volume does not alter the ability of these variables to detect a positive response or the repeatability of the measurement.

Comparison of impulse oscillometry and spirometry for detection of airway hyperresponsiveness to methacholine, mannitol, and eucapnic voluntary hyperventilation in children

“…In the mannitol group, we observed a weak but statistically significant correlation between IOS indexes and drop in FEV1. McClean et al described a strong correlation between AHR measured by spirometry and the forced oscillation technique (FOT; which is similar to IOS but uses the sum of several sinusoidal waves instead of pressure pulses). Horsman et al also found a significant correlation between FEV1 and R5 changes, but not for R20.…”

Contrasting diagnosis performance of forced oscillation and spirometry in patients with rheumatoid arthritis and respiratory symptoms

“…Examples of recent research include the evaluation of lung function in children with repaired tracheo-oesophageal fistula (51), the detection of upper airway obstruction in patients with tracheal stenosis (52), the determination of airway hyperresponsiveness during mannitol challenge (53), and the analysis of patients with suspicion of acute lung rejection under circumstances when spirometry could not be correctly performed (54). Guo and collaborators (55) investigated the identification of DPOC in elderly subjects through the FOT and obtained maximum AUC values of 0.85, indicating an accurate detection.…”

Mechanisms of airway hyper‐responsiveness in asthma: the past, present and yet to come

“…Recent advancements have allowed the FOT to cross the divide into clinical practice. FOT is capable of detecting patients with AHR, as assessed by spirometry, during methacholine (34), mannitol (35) and carbachol challenges (36). Furthermore, the repeatability of Grs and Xrs is not different to that of FEV 1 (2.0 and 1.95 vs 1.67 doubling doses, respectively, (35)).…”

“…FOT is capable of detecting patients with AHR, as assessed by spirometry, during methacholine (34), mannitol (35) and carbachol challenges (36). Furthermore, the repeatability of Grs and Xrs is not different to that of FEV 1 (2.0 and 1.95 vs 1.67 doubling doses, respectively, (35)). However, it should be noted that the aforementioned comparative studies included deep inspirations (inherent in spirometry) which provide beneficial effects in non-asthmatic but not moderate to severe asthmatic subjects (37).…”