Diffusion capacity and CT measures of emphysema and airway wall thickness – relation to arterial oxygen tension in COPD patients

Figures & data

Table 1 Characteristics of study participants (n=271)

Variable	Total	Female	Male	p
Age, mean years (SD)	64.2 (6.7)	63.2 (6.4)	64.8 (6.9)	0.06
Current smoking status, n (%)^a	112 (41)	37 (36)	75 (45)	0.18
Height, mean cm (SD)	171.6 (8.4)	164.1 (5.8)	176.2 (6.3)	<0.01
Weight, mean kg (SD)	75.1 (17.4)	68.6 (17.3)	79.0 (16.3)	<0.01
BMI, mean kg/m^2 (SD)	25.4 (5.3)	25.4 (5.9)	25.4 (4.9)	0.98
PaO2, mean kPa (SD)	9.36 (1.13)	9.17 (1.14)	9.48 (1.11)	0.03
PaCO2, mean kPa (SD)	5.26 (0.48)	5.21 (0.49)	5.28 (0.47)	0.23
Hypoxaemia status, n (%)	33 (12.2)	20 (19.6)	13 (7.7)	<0.01
Haemoglobin, mean g/dl (SD)^b	14.4 (1.2)	13.9 (1.1)	14.8 (1.1)	<0.01
FEV1, mean % pred (SD)	50 (14.6)	53.2 (13.5)	48.1 (15.0)	<0.01
FEV/FVC-ratio, median (IQR)	0.46 (0.37–0.55)	0.49 (0.40–0.58)	0.44 (0.35–0.51)	<0.01
GOLD category, n (%)
II	134 (49)	58 (57)	76 (45)	0.02
III	110 (41)	40 (39)	70 (41)
IV	27 (10)	4 (4)	23 (14)
DLCO, mean (SD)	5.16 (1.92)	4.52 (1.58)	5.55 (2.01)	<0.01
DLCO, mean % pred. (SD)	58.4 (18.7)	61.5 (19.3)	56.6 (18.1)	0.04
VA, mean litres (SD)	4.94 (1.07)	4.1 (0.63)	5.5 (0.93)	<0.01
KCO (DLCO/VA), mean (SD)	1.04 (0.31)	1.10 (0.31)	1.01 (0.30)	0.01
LAA both lungs, median (IQR)	13.3 (5.2–19.3)	10.7 (3.9–14.8)	14.9 (6.2–21.8)	<0.01
AWT–Pi10, mean (SD)^b	4.36 (0.11)	4.31 (0.12)	4.38 (0.10)	<0.01
Total, n (%)	271	102 (38)	169 (62)

^a p-values are from two-group mean comparison tests (unpaired t-tests) and Wilcoxon rank-sum tests for continuous variables and Pearson's chi-squared tests for categorical variables.

^bMissing information for current smoking status and AWT–Pi10 (n=1) and for haemoglobin (n=2).

PaO₂, Partial pressure of arterial oxygen; PaCO₂, Partial pressure of arterial carbon dioxide; BMI, body mass index; FEV₁, Forced expiratory volume in 1 second; FVC, Forced vital capacity; GOLD, Global Initiative for Chronic Obstructive Lung Disease; DLCO, diffusing capacity of the lung for carbon monoxide; KCO, carbon monoxide transfer coefficient; VA, Alveolar volume; %LAA, percentage low attenuation areas; AWT–Pi10, airway wall thickness at an internal perimeter of 10 mm; SD, standard deviation; IQR, inter quartile range.

Table 2 Mean (SD) PaO₂ by tertiles of %LAA, AWT–Pi10, DLCO, and KCO

	PaO2 (kPa)
All subjects	9.34 (1.13)
Groups by tertiles of LAA
I (0.27–6.50)	9.65 (1.14)
II (6.50–15.61)	9.30 (1.18)
III (15.61–53.11)	9.02 (1.05)
p-value (one-way ANOVA)	<0.001
p-value (NP trend)^a	<0.001
Groups by tertiles of AWT-Pi10
I (3.95–4.30)	9.31 (0.93)
II (4.30–4.40)	9.35 (1.17)
III (4.40–4.87)	9.28 (1.29)
p-value (one-way ANOVA)	0.911
p-value (NP trend)	0.904
Groups by tertiles of DLCO
I (1.80–4.18)	8.97 (1.05)
II (4.18–5.61)	9.39 (1.11)
III (5.61–13.91)	9.76 (1.10)
p-value (one-way ANOVA)	<0.001
p-value (NP trend)	<0.001
Groups by tertiles of KCO
I (0.35–0.89)	9.06 (1.04)
II (0.89–1.16)	9.37 (1.16)
III (1.16–2.15)	9.71 (1.10)
p-value (One-way ANOVA)	<0.001
p-value (NP trend)	<0.001

Significant p-values are indicated in bold

^aNP trend: nonparametric test for trend across ordered groups.

%LAA, percentage low attenuation areas; AWT-Pi10, airway wall thickness at an internal perimeter of 10 mm; DLCO, diffusing capacity of the lung for carbon monoxide; KCO, carbon monoxide transfer coefficient; SD, standard deviation.

Table 3 Multiple linear regression with %LAA, AWT-Pi10, and diffusion capacity (DLCO or KCO) in four separate models

		Outcome variable PaO2 (kPa)
		Unadjusted	Adjustment group 1	Adjustment group 2
Model	Explanatory variable	Coefficient (CI) p	Coefficient (CI) p	Coefficient (CI) p
1	%LAA	−0.023−0.023(−0.038–(−0.014)) p <0.001	−0.032−0.032(−0.044–(−0.019)) p <0.001	−0.009 (−0.024–0.006) p=0.215
2	AWT-Pi10	−0.174 (−1.27–0.92) p=0.76	−0.63 (−1.78–0.51) p=0.279	−0.751 (−1.82–0.32) p=0.167
3	DLCO	0.2060.206(0.14–0.27) p <0.001	0.2200.220(0.15–0.29) p <0.001	0.1490.149(0.07–0.23) p =0.001
4	KCO	0.9890.989(0.57–1.49) p <0.001	1.061.06(0.640–1.49) p <0.001	0.6940.694(0.251–1.13) p =0.002

Adjustment group 1=adjusted for sex, age, smoking status, and haemoglobin (in analyses with DLCO and KCO).

Adjustment group 2=adjusted for sex, age, smoking status, haemoglobin (in analyses with DLCO and KCO), and FEV₁. Significant results are indicated in bold.

%LAA, percentage low attenuation areas; AWT-Pi10, airway wall thickness at an internal perimeter of 10 mm; DLCO, diffusing capacity of the lung for carbon monoxide; KCO, carbon monoxide transfer coefficient; CI confidence interval.

Table 4 Multiple linear regression with %LAA and diffusion capacity (DLCO or KCO) in the same model

	Outcome variable PaO2 (kPa)
	Adjustment group 1	Adjustment group 2
Explanatory variables	Coefficient (CI) p	Coefficient (CI) p
%LAA	−0.006 (−0.02–0.01) p=0.446	0.004 (−0.01–0.02) p=0.651
DLCO	0.200 (0.10–0.30) p <0.001	0.1660.166(0.07–0.26) p =0.001
%LAA	−0.013 (−0.03–0.005) p=0.151	0.008 (−0.01–0.03) p=0.458
KCO	0.777 (0.19–1.36) p =0.010	0.8470.847(0.28–1.42) p =0.004

Adjustment group 1=adjusted for sex, age, smoking status, and haemoglobin (in analyses with DLCO and KCO).

Adjustment group 2=adjusted for sex, age, smoking status, haemoglobin (in analyses with DLCO and KCO), and FEV₁.

Significant results are indicated in bold.

%LAA, percentage low attenuation areas; DLCO, diffusing capacity of the lung for carbon monoxide; KCO, carbon monoxide transfer coefficient; CI, confidence interval.