Feasibility and challenges of using multiple breath washout in COPD

Figures & data

Table 1 Clinical characteristics and lung function measurements

Clinical characteristics	COPD (n=54)
	Absolute values	% predicted
Sex (male/female)	37/17
Age (years)	66 (7)
Height (m)	1.67 (0.10)
Weight (kg)	78.8 (18.6)
Body mass index (kg/m^2)	27.8 (4.9)
Smoking history (pack years)a	42.1 (31.7–55.5)
Spirometry
FEV1 (L)	1.68 (0.6)	63.1 (18.4)
FEF25%–75% (L/s)	0.66 (0.35)	22.0 (11.2)
FVC (L)	3.62 (1.0)	106.6 (17.8)
FEV1/FVC	0.48 (0.13)
Multiple breath nitrogen washout
MBWN2 test time (mins)	38.4 (19.9)
FRCN2 (L)	4.35 (1.27)	135.7 (36.8)
LCIN2	12.1 (2.2)	158.9 (29.3)
Plethysmography
TLC (L)	6.30 (1.27)	105.5 (15.4)
Inspiratory capacity (L)	2.15 (0.59)	78.4 (15.2)
FRCpleth (L)	3.99 (1.06)	123.0 (29.8)
RV (L)	2.95 (0.97)	127.9 (40.7)
RV/TLC %	46.6 (10.5)
Gas transfer
DLCO (mmol⋅min^−1⋅kPa^−1)	5.23 (1.78)	63.1 (18.4)
KCO (mmol⋅min^−1⋅kPa^−1)	1.07 (0.28)	79.6 (23.2)
Forced oscillation
R5–R20 a (kPa/L/s)	0.17 (0.11–0.25)
X5 (kPa/L/s)	−0.30 (0.16)
CAT scorea	18.0 (9.0–25.3)

Note: Parametric data are expressed as mean and SD except

a median and inter-quartile range.

Abbreviations: CAT, COPD Assessment Test; DL_co, carbon monoxide diffusing capacity; FEF, forced expiratory flow; FEV₁, forced expiratory volume in 1 second; FRC, functional residual capacity; FRC_N2, FRC measured by nitrogen washout; FRCpleth, FRC measured by plethysmography; FVC, forced vital capacity; K_CO, carbon monoxide transfer coefficient; LCI_N2, lung clearance index measured by nitrogen washout; MBW_N2, multiple-breath washout using nitrogen; RV, residual volume; TLC, total lung capacity.

Figure 1 COPD LCI_N2 Z-score versus FEV₁ Z-score.

Notes: Z-scores were calculated using the GLI 2012 reference equations for FEV₁¹⁷ and those provided by Ecomedics for LCI. The horizontal dotted line represents the upper limit of normal for LCI_N2. The vertical dotted line represents the FEV₁ Z-score of −1.65 (lower limit of normal range).
Abbreviations: FEV₁, forced expiratory volume in 1 second; GLI, global lung initiative; LCI_N2, lung clearance index measured by nitrogen washout.

Figure 2 LCI_N2 versus COPD GOLD stage.

Abbreviations: GOLD, Global Initiative for Obstructive Lung Disease; LCI_N2, lung clearance index measured by nitrogen washout

Table 2 Clinical characteristics and lung function measurements of COPD patients with paired MBW assessments

Clinical parameter	COPD (n=17)	p-value
FRC (L)
FRCN2	4.24 (1.47)
FRCSF6	3.49 (1.00)	0.002
FRC (%) predicted
FRCN2	136.8 (42.8)	0.002
FRCSF6	112.4 (28.0)
Lung clearance index
LCIN2	12.3 (2.2)
LCISF6	11.9 (3.1)	0.4
FEV1(%)	64.2 (21.1)
FVC (%)	101.4 (13.6)
FEV1/FVC	0.5 (0.1)

Note: Parametric data are expressed as mean and SD, and comparisons were performed using Student’s t-test.

Abbreviations: FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; FRC, functional residual capacity; FRC_N2, FRC measured by nitrogen washout; FRC_SF6, FRC measured by sulphur hexafluoride washout; LCI_N2, lung clearance index measured by nitrogen washout; LCI_SF6, lung clearance index measured by sulphur hexafluoride washout; MBW, multiple-breath washout.

Figure 3 Bland–Altman comparison between FRC_N2 and FRC_pleth in subjects with COPD.

Notes: The central dotted line represents the mean difference, and the upper and lower dotted lines represent the limits of agreement. The vertical line represents hyper-inflation, defined as FRC_N2 >120% predicted. Data points plotted above the x-axis represent subjects in which FRC_N2 was greater than FRC_pleth.
Abbreviations: FRC, functional residual capacity; FRC_N2, FRC measured by nitrogen washout; FRC_pleth, FRC measured by plethysmography.

OostveenEMacLeodDLorinoHERS Task Force on Respiratory Impedance Measurements. The forced oscillation technique in clinical practice: methodology, recommendations and future developmentsEur Respir J20032261026104114680096

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