Table 4 Baseline characteristics and diaphragm function parameters of frequent and infrequent AECOPD patients

Age (year)

57.89 ± 6.94

62.61 ± 5.37

 − 2.94

0.005

BMI (kg/cm²)

25.46 ± 2.56

23.11 ± 2.64

3.47

0.001

CAT score

10.89 ± 3.04

16.42 ± 7.55

 − 3.62

0.001

mMRC

1 (1,1)

2 (1,3)^a

 − 3.19

0.001

6MWD(m)

500.07 ± 60.66

399.19 ± 109.46

4.31

P < 0.001

FEV1(L)

2.11 ± 0.95

1.30 ± 0.67

3.82

P < 0.001

FEV1/%pre

63.41 ± 20.27

40.44 ± 18.11

4.60

P < 0.001

FVC(L)

3.27 ± 0.81

2.63 ± 0.94

2.80

0.007

FVC/%pre

83.22 ± 16.40

65.85 ± 21.97

3.41

0.001

GOLDI

8 (28.57%)

1 (3.23%)

–

–

GOLDII

11 (39.29%)

8 (25.81%)

–

–

GOLDIII

9 (32.14%)

9 (29.03%)

–

–

GOLDIV

0 (0%)

13 (41.94%)

–

–

Diaphragmatic dome factor (Insp)

1.17 ± 0.10

1.13 ± 0.07

1.65

0.105

Diaphragmatic dome factor (Exp)

1.25 ± 0.07

1.23 ± 0.17

0.71

0.480

Chest wall motion(cm)

2.35 ± 1.05

1.51 ± 0.93

3.25

0.002

Change of lung area (cm²)

126.71 ± 37.79

96.76 ± 37.62

3.05

0.003

Diaphragmatic displacement (cm)

5.33 ± 1.99

3.10 ± 1.36

4.98

P < 0.001

Diaphragm thickening fraction

39.83 ± 16.25

19.36 ± 9.38

5.84

P < 0.001