Impulse oscillometry system as an alternative diagnostic method for chronic obstructive pulmonary disease

Abstract

We aimed to compare impulse oscillation system (IOS) and traditional pulmonary function tests (PFTs) for the assessment of the severity of chronic obstructive pulmonary disease (COPD), and to assess the use of IOS parameters to identify patients who were forced expiratory volume in 1 second (FEV1)%pred < 50%.Patients with COPD (n = 215) were enrolled at the Ninth Hospital of Xi'an Affiliated Hospital of Xi'an Jiaotong University between October 2014 and September 2016. All patients were assessed by traditional PFT and IOS. Diagnostic performance of IOS parameters to determine indication for patients of FEV1%pred < 50% was assessed on receiver-operating characteristics (ROC) curve analysis.Out of 215 patients, 18, 83, 78, and 36 patients were classified as grade 1, 2, 3, and 4, respectively, according to the Global Initiative for Chronic Obstructive Lung Disease (GOLD) severity grading. On Spearman correlation analysis, FEV1%pred, MMEF 75%-25%, and residual volume/total lung capacity (RV/TLC) correlated with total respiratory impedance (Z5)%pred, resistance at 5 Hz (R5)-resistance at 20 Hz (R20), R5-R20% R5, R5, R5%pred, frequency response (Fres), reactance area (Ax), and reactance at 5 Hz (X5). On ROC curve analysis, the area under the curve (AUC) of X5 absolute value, Fres, Ax, Z5%pred, R5-R20, and R5-R20% R5 were 0.748, 0.755, 0.760, 0.705, 0.715, and 0.735, respectively, for COPD patients who required inhalational glucocorticoid therapy.IOS parameters showed a good correlation with traditional pulmonary function parameters; reactance parameters showed a stronger correlation than that of the resistance parameters. IOS can be used as an alternative method for pulmonary function assessment in patients with COPD with FEV1%pred < 50% who need inhalational glucocorticoid therapy.

Clinical trial registration number: ChiCTR-OCH-14004904.

Figure 1

Flow chart showing patient selection.

Figure 2

Trends of IOS parameters in GOLD pulmonary function classification. (A) Z5%pred and R20%pred; (B) R5%pred and (R5-R20)% R5 ^∗ 100; (C) R5, R20, R5-R20, X5; and (D) Ax and Fres.

Figure 3

Trends of resistance and reactance parameters in GOLD pulmonary function classification. (A) Resistance parameters Z5%pred, R5%pred, and (R5-R20)% R5 ^∗ 100; (B) reactance parameters X5 and Ax; and (C) reactance parameters Fres. Ax = reactance area, Fres = frequency response, GOLD = Global Initiative for Chronic Obstructive Lung Disease, %pred = of the predicted value, R20 = resistance at 20 Hz, R5 = resistance at 5 Hz, X5 = reactance at 5 Hz, Z5 = total respiratory impedance.

Figure 4

Spearman correlation analysis of FEV1%pred and IOS parameters. (A) Z5%pred (r = −0.435^∗∗); (B) R5%pred (r = −0.350^∗∗); (C) R20%pred r = −0.104; (D) (R5-R20)%R5 (r = −0.474^∗∗); G = Ax (r = −0.521^∗∗); (E) X5 (r = 0.540^∗∗); (F) Fres (r = −0.474^∗∗). Ax = reactance area, FEV1 = forced expiratory volume in one second, Fres = frequency response, IOS = impulse oscillometry system, %pred = of the predicted value, R20 = resistance at 20 Hz, R5 = resistance at 5 Hz, X5 = reactance at 5 Hz, Z5 = total respiratory impedance.

Figure 5

Spearman correlation analysis of MMEF75%–25%pred and IOS parameters. (A) Z5%pred (r = −0.439^∗∗); (B) R5%pred (r = −0.354^∗∗); (C) R20%pred (r = −0.108); (D) (R5-R20)%R5^∗100 (r = −0.489^∗∗); (E) X5 (r = 0.569^∗∗); (F) Fres (r = −0.510^∗∗); (G) Ax (r = −0.540^∗∗). Ax = reactance area, Fres = frequency response, IOS = impulse oscillometry system, MMEF75%–25% = maximal mid expiratory flow, %pred = of the predicted value, R20 = resistance at 20 Hz, R5 = resistance at 5 Hz, X5 = reactance at 5 Hz, Z5 = total respiratory impedance.

Figure 6

Spearman correlation analysis of RV/TLC and IOS parameters, (A) Z5%pred (r = 0.268^∗∗); (B) R5%pred (r = 0.189^∗∗); (C) R20%pred (r = −0.060); (D) (R5-R20)%R5^∗100 (r = 0.398^∗∗); (E) X5 (r = −0.436^∗∗); (F) Fres (r = 0.350^∗∗); (G) Ax (r = 0.401^∗∗). Ax = reactance area, Fres = frequency response, IOS = impulse oscillometry system, %pred = of the predicted value, R20 = resistance at 20 Hz, R5 = resistance at 5 Hz, RV/TLC = residual volume/total lung capacity, X5 = reactance at 5 Hz, Z5 = total respiratory impedance.

Figure 7

ROC curves of IOS parameters and combination of parameters to diagnose FEV1%pred <50% of the COPD population. COPD = chronic obstructive pulmonary disease, FEV1 = forced expiratory volume in one second, IOS = impulse oscillometry system, %pred = of the predicted value, ROC = receiver-operating characteristic.