Bronchodilator Responses in Respiratory Impedance, Hyperinflation and Gas Trapping in COPD

Figures & data

Table 1. Subject demographics.

N (male)	15 (11)
Age (range), years	68 (58–79)
Smoking history, pack years	43 (33)
FEV1, %pred	64 (17)
FEV1, Z-score	−2.10 (1.1)
FVC, %pred	95 (17)
FVC, Z-score	−0.16 (1.2)
FEV1/FVC, %	51 (9.6)
FEV1/FVC, Z-score	−2.93 (0.98)
TLC, %pred	104 (16)
FRC, %pred	120 (26)
RV, %pred	112 (29)
RV/TLC, %pred	104 (23)
IC/TLC %	0.39 (0.06)
DLCOCorr, %pred	72 (14)
R5, cmH2O.s.L^−^1	5.30 (2.6)
R5, Z-score	1.66 (1.7)
X5, cmH2O.s.L^−^1	−3.50 (3.0)
X5, Z-score	−3.79 (4.9)
AX, cmH2O.L^−^1	38.01 (39)
AX, Z-score	2.91 (1.5)

All values presented as mean (SD) unless otherwise stated. %pred, percent of predicted from published reference equations(11,19–21); FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; TLC, total lung capacity; FRC, functional residual capacity; RV, residual volume; DLCO_corr, diffusing capacity for carbon monoxide corrected for current haemoglobin; R5, resistance at 5 Hz; X5, reactance at 5 Hz; AX, area under the reactance curve from 5 Hz to resonant frequency.

Table 2. Spirometry, lung volumes and forced oscillation technique (FOT) measurements pre- and 2 hrs-post long-acting bronchodilator.

	Baseline	2 hr post-BD	Absolute change	% change
	Mean (SD)	Mean (SD)	Mean (SD)	Mean (SD)	Z	p
FEV1, L	1.98 (0.78)	2.14 (0.71)	0.15 (0.13)^**	10.3 (8.6)	−2.84	0.004
FVC, L	3.83 (1.1)	4.04 (0.99)	0.21 (0.33)^*	7.9 (16)	−2.22	0.03
TLC, L	6.77 (1.3)	6.70 (1.3)	−0.06 (0.22)	−0.8 (3.5)	−0.91	0.4
IC, L	2.61 (0.77)	2.83 (0.78)	0.22 (0.29)^*	9.8 (12)	−2.53	0.01
FRC, L	4.15 (4.2)	3.87 (0.82)	−0.28 (0.35)^*	−6.1 (7)	−2.56	0.01
RV, L	2.85 (0.82)	2.62 (0.54)	−0.23 (0.42)	−5.6 (12)	−1.90	0.06
RV/TLC %	0.42 (0.10)	0.39 (0.06)	−0.03 (0.05)	−4.9 (10)	−1.71	0.09
IC/TLC %	0.39 (0.09)	0.42 (0.07)	0.03 (0.04)^**	10.5 (12)	−2.78	0.005
R5, cmH2O.s.L^−^1	4.98 (2.6)	3.98 (2)	−1.01 (1.1)^**	−17.8 (20)	−2.85	0.005
R5in, cmH2O.s.L^−^1 ^$	5.28 (3.1)	3.81 (1.8)	−1.71 (1.6) ^**	−27.0 (21)	−2.83	0.005
R19, cmH2O.s.L^−^1	3.15 (0.91)	2.88 (0.85)	−0.27 (0.47)	−7.85 (15)	−1.93	0.053
R5-R19, cmH2O.s.L^−^1	1.86 (1.8)	1.13 (1.3)	−0.73 (0.81)^**	−18.9 (196)	−2.76	0.006
X5, cmH2O.s.L^−^1	−3.45 (3.4)	−2.25 (1.9)	1.20 (1.9) ^*	25.0 (31)	−2.41	0.046
X5in, cmH2O.s.L^−^1 ^$	−3.25 (2.7)	−1.98 (1.1)	1.27 (1.8) ^**	27.8 (28)	−2.83	0.005
AX, cmH2O2.s.L^−^1	36.52 (43)	20.97 (28)	−15.56 (20) ^*	−35.1 (36)	−2.41	0.02
X5in-ex, cmH2O.s.L^−^1 ^$	1.03 (1.8)	0.99 (1.6)	−0.04 (1.1)	51.0 (168)	−0.11	0.9

Wilcoxon matched-pairs signed rank test. FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; TLC, total lung capacity; IC, inspiratory capacity; FRC, functional residual capacity; RV, residual volume; R5, resistance at 5 Hz; R19, resistance at 19 Hz; R5-R19, resistance at 5 Hz minus resistance at 19 Hz; X5, reactance at 5 Hz; R5_in and X5_in, inspiratory phases of resistance and reactance at 5 Hz; AX, area under the reactance curve from 5 Hz to resonant frequency; X5_in-ex, inspiratory phase minus expiratory phase of reactance at 5 Hz.

^$ Missing data (n = 1) for intrabreath FOT values.

^* p < 0.05,

^** p < 0.01 for absolute change.

Table 3. Relationships between forced oscillation technique (FOT), hyperinflation and gas trapping pre-long-acting bronchodilator.

	IC/TLC		RV/TLC
	Unadjusted	Adjusted^†	Unadjusted	Adjusted^‡
Spirometry ^#
FEV1	0.52^*	0.40	−0.59^*	−0.51
FEV1 Z-score	0.48	0.44	−0.58^*	−0.61^*
FEV1/FVC	0.59^*	0.58^*	−0.31	−0.48
FEV1/FVC Z-score	0.56^*	0.55^*	−0.28	−0.53^*
Unadjusted FOT parameters
R5	−0.45	−0.39	0.43	0.42
R5in ^$	−0.57^*	−0.58^*	0.32	0.39
R19	−0.55^*	−0.45	0.43	0.48
R5-R19	−0.46	−0.44	0.39	0.37
X5	0.43	0.39	−0.42	−0.30
X5in ^$	0.66^*	0.68^**	−0.36	−0.39
AX	−0.49	−0.44	0.44	0.41
X5in-ex ^$	−0.47	−0.42	0.61^*	0.35
Adjusted FOT parameters ^⋀
R5	−0.62^*	−0.63^*	0.34	0.46
R5in ^$	−0.62^*	−0.73^*	0.30	0.37
R19	−0.55^*	−0.55^*	0.27	0.34
R5-R19	−0.61^*	−0.71^**	0.40	0.46
X5	0.47	0.49	−0.36	−0.34
X5in ^$	0.56^*	0.68 ^**	−0.34	−0.42
AX	−0.53^*	−0.53^*	0.37	0.39
X5in-ex ^$	−0.54^*	−0.61^*	0.54^*	0.54^*

Spearman rank correlation coefficients. See main text for abbreviations. Adjusted values are as follows:

^† unstandardised residuals from linear regression with age as independent variable

^‡ Z-scores from Quanjer et al [20]

^# Z-scores from Quanjer et al [19]

^⋀ Z-scores from Oostveen et al [11] (for R5, X5 and AX), or unstandardised residuals from multiple linear regression with age, sex, height and weight as independent variables (for R5_in, R19, R5-R19, X5_in and X5_in-ex).

^$ Missing data (n = 1) for intrabreath FOT values.

^* p < 0.05,

^** p < 0.01.

Figure 1. Relationship between forced oscillation technique (FOT), and hyperinflation and gas trapping, before and 2 hours post-long-acting bronchodilator.

Table 4. Relationship between change in forced oscillation technique (FOT) and change in hyperinflation and gas trapping from baseline to 2 hrs post-long-acting bronchodilator.

	Δ(IC/TLC)	Δ(RV/TLC)
Change in spirometry
ΔFEV1	0.58^*	−0.31
Δ(FEV1/FVC)	0.07	0.37
Change in FOT parameters
ΔR5	−0.34	0.60^*
ΔR5in ^$	−0.51	0.75^**
ΔR19	−0.30	0.32
ΔR5-R19	−0.40	0.70^**
ΔX5	0.48	−0.74^**
ΔX5in ^$	0.57^*	−0.74^**
ΔAX	−0.54^*	0.82^**
ΔX5in-ex ^$	−0.15	0.19

Spearman rank correlation. See main text for abbreviations.

^$ Missing data (n = 1) for intrabreath FOT values.

^* p < 0.05,

^** p < 0.01.

Table 5. Relationship between baseline forced oscillation technique (FOT), and subsequent change in hyperinflation and gas trapping 2 hrs post-long-acting bronchodilator.

	Δ(IC/TLC)	Δ(RV/TLC)
Spirometry ^#
FEV1	−0.35	0.58 ^*
Z-FEV1	−0.45	0.63 ^*
FEV1/FVC	−0.47	0.64 ^*
Z-FEV1/FVC	−0.43	0.68 ^**
Unadjusted FOT parameters
R5	0.53 ^*	−0.66 ^**
R5in ^$	0.45	−0.72 ^**
R19	0.36	−0.68 ^**
R5-R19	0.53 ^*	−0.62 ^*
X5	−0.50	0.53 ^*
X5in ^$	−0.52	0.62 ^*
AX	0.50	−0.69 ^**
X5in-ex ^$	0.44	−0.58 ^*
Adjusted FOT parameters ^⋀
R5	0.59 ^*	−0.74 ^**
R5in ^$	0.53 ^*	−0.59 ^*
R19	0.44	−0.57 ^*
R5-R19	0.61 ^*	−0.61 ^*
X5	−0.53 ^*	0.60 ^*
X5in ^$	−0.60 ^*	0.50
AX	0.56 ^*	−0.71 ^**
X5in-ex ^$	0.62 ^*	−0.76 ^**

Spearman rank correlation. See main text for abbreviations. Adjusted values are as follows:

^# Z-scores from Quanjer et al [19]

^⋀ Z-scores from Oostveen et al [11] (for R5, X5 and AX), or unstandardised residuals from multiple linear regression with age, sex, height, and weight as independent variables (for R5_in, R19, R5-R19, X5_in, and X5_in-ex).

^$ Missing data (n = 1) for intrabreath FOT values.

^* p < 0.05,

^** p < 0.01.

Figure 2. Relationship between baseline forced oscillation technique (FOT) and subsequent change in hyperinflation and gas trapping 2 hours post-long-acting bronchodilator.

Figure 3. Relationship between reactance and communicating lung volume.

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