The phenotype of concurrent chronic bronchitis and frequent exacerbations in patients with severe COPD attending Swedish secondary care units

Figures & data

Table 1 Patient characteristics by chronic bronchitis and frequent exacerbations

Patient characteristics	Chronic bronchitis		P-value	Frequent exacerbations		P-value
	No (n=235)	Yes (n=138)		No (n=189)	Yes (n=184)
Sex
Male	105 (44.7%)	60 (43.5%)	Ref	99 (52.4%)	109 (59.2%)	Ref
Female	130 (55.3%)	78 (56.5%)	0.821	90 (47.6%)	75 (40.8%)	0.182
Age	71.2 (±8.31)	71.3 (±7.02)	0.919	71.2 (±7.79)	71.3 (±7.93)	0.938
Smoking habits
Never or ex-smoker	209 (88.9%)	103 (74.6%)	Ref	155 (82.0%)	156 (85.2%)	Ref
Current smoker	26 (11.1%)	35 (25.4%)	,0.0001	34 (18.0%)	27 (14.7%)	0.399
COPD stage
III	170 (72.3%)	89 (64.5%)	Ref	150 (79.4%)	109 (59.2%)	Ref
IV	65 (27.7%)	49 (35.5%)	0.112	39 (20.6%)	75 (40.8%)	<0.0001
FEV1 % pred	35.2 (±8.57)	34.0 (±8.87)	0.176	56 (29.6%)	82 (44.6%)	0.003
Body mass index
≤22.0	66 (28.1%)	48 (34.8%)	0.155	50 (26.5%)	64 (34.8%)	0.155
>22.0, ≤30.0	139 (59.1%)	72 (52.2%)	Ref	110 (58.2%)	101 (54.9%)	Ref
>30.0	30 (12.8%)	18 (13.0%)	0.658	29 (15.3%)	19 (10.3%)	0.300
Frequent exacerbations	102 (43.4%)	82 (59.4%)	0.003	–	–	–
Chronic bronchitis	–	–	–	52 (29.6%)	114 (44.6%)	0.003
Cardiovascular disease	140 (59.6%)	83 (60.1%)	0.914	109 (57.7%)	114 (62.0%)	0.399
Diabetes	23 (9.8%)	17 (12.3%)	0.446	20 (10.6%)	20 (10.9%)	0.928
Renal impairment	9 (3.8%)	5 (3.6%)	0.919	7 (3.7%)	7 (3.8%)	0.959
Musculoskeletal symptoms	45 (19.1%)	45 (32.6%)	0.003	36 (19.0%)	54 (29.3%)	0.020
Osteoporosis	57 (24.3%)	46 (33.3%)	0.058	43 (22.8%)	60 (32.6%)	0.033
Depression	33 (14.0%)	29 (21.0%)	0.081	27 (14.3%)	35 (19.0%)	0.219

Note: Data presented as numbers (%) of characteristics or mean (± standard deviations) as compared with the remaining study population.

Abbreviations: n, number of patients; FEV₁% pred, forced expiratory volume in 1 second as a percentage of predicted value; Ref, reference.

Figure 1 Categories of the response variable in multi-nominal logistic regression.

Note: Data presented as numbers (percentages) of the total study population.

Abbreviations: CB, chronic bronchitis; Ex, frequent exacerbations; No CB or Ex, no chronic bronchitis and no frequent exacerbations; CB + Ex, both chronic bronchitis and frequent exacerbations.

Figure 2 Clinical characteristics in different phenotypes.

Note: Proportion of clinical characteristics in different phenotypes, expressed as percentages.
Abbreviations: CB, chronic bronchitis; Ex, frequent exacerbations; No CB or Ex, no chronic bronchitis and no frequent exacerbations; CB + Ex, both chronic bronchitis and frequent exacerbations.

Table 2 Logistic regression analyses

Explanatory variables	Chronic bronchitis Unadjusted OR (95% CI)	P-value	Chronic bronchitis Adjusted OR (95% CI)	P-value
Current smoker	2.73 (1.56–4.78)	<0.0001	2.75 (1.54–4.91)	0.001
Frequent exacerbations	1.91 (1.25–2.93)	0.003	1.93 (1.24–3.01)	0.004
Musculoskeletal symptoms	2.04 (1.26–3.31)	0.004	1.74 (1.05–2.86)	0.031
	Frequent exacerbations Unadjusted OR (95% CI)	P-value	Frequent exacerbations Adjusted OR (95% CI)	P-value
FEV1 % pred	0.96 (0.93–0.98)	<0.0001	0.96 (0.94–0.98)	0.001
Chronic bronchitis	1.91 (1.25–2.93)	0.003	1.73 (1.11–2.68)	0.015
Musculoskeletal symptoms	1.77 (1.09–2.86)	0.021	1.51 (0.91–2.53)	0.114
Osteoporosis	1.64 (1.04–2.60)	0.034	1.29 (0.79–2.10)	0.314

Note: In the multivariate analyses, all variables with a statistically significant association in the univariate analyses were included and presented in the table.

Abbreviations: OR, odds ratio; CI, confidence interval; FEV₁% pred, forced expiratory volume in 1 second as a percentage of predicted value.

Table 3 Multinominal regression

Variables	No chronic bronchitis, no frequent exacerbations (n=133)	No chronic bronchitis, but frequent exacerbations (n=102)	P-value	Chronic bronchitis, but no frequent exacerbations (n=56)	P-value	Chronic bronchitis, and frequent exacerbations (n=82)	P-value
Current smoker	Ref	0.67 (0.28–1.58)	0.359	2.94 (1.35–6.39)	0.006	1.84 (0.86–3.94)	0.115
FEV1 % pred	Ref	0.97 (0.94–1.00)	0.079	1.01 (0.97–1.05)	0.617	0.95 (0.92–0.98)	0.002
Musculoskeletal symptoms	Ref	1.20 (0.61–2.37)	0.600	1.08 (0.48–2.42)	0.858	2.55 (1.31–4.99)	0.006
Osteoporosis	Ref	1.60 (0.85–3.00)	0.142	1.82 (0.86–3.84)	0.116	1.59 (0.82–3.10)	0.172

Note: In the multivariate analysis, all variables with a statistically significant association in the univariate analyses were included and presented in the table. Data are presented as adjusted OR (95% CI).

Abbreviations: OR, odds ratio; CI, confidence interval; FEV₁% pred, forced expiratory volume in 1 second as a percentage of predicted value; Ref, reference.

Figure 3 COPD phenotypes and patient characteristics.

Note: Venn diagram showing the proportional distribution of different phenotypes in the study population, and the associations of different patient characteristics in logistic regression analyses.
Abbreviations: CB, chronic bronchitis; Ex, frequent exacerbations; No CB or Ex, no chronic bronchitis and no frequent exacerbations; CB + Ex, both chronic bronchitis and frequent exacerbations.

Table 4 Sex differences in multinominal regression

Explanation variables	Male Adjusted OR (95% CI)	P-value	Female Adjusted OR (95% CI)	P-value	P-value interaction
Both chronic bronchitis and frequent exacerbations
Current smoker	0.65 (0.19–2.28)	0.502	3.86 (1.31–11.4)	0.015	0.040
FEV1 % pred	0.91 (0.86–0.96)	0.001	0.97 (0.93–1.02)	0.202	0.075
Musculoskeletal symptoms	2.74 (0.86–8.77)	0.090	2.45 (1.06–5.66)	0.036	0.810
Osteoporosis	1.19 (0.32–4.42)	0.798	1.91 (0.85–4.32)	0.120	0.275
Chronic bronchitis but no frequent exacerbations
Current smoker	2.47 (0.86–7.11)	0.095	4.28 (1.26–14.5)	0.020	0.339
FEV1 % pred	1.01 (0.95–1.07)	0.812	1.01 (0.96–1.07)	0.741	0.972
Musculoskeletal symptoms	0.20 (0.02–1.74)	0.144	2.13 (0.78–5.80)	0.139	0.028
Osteoporosis	0.68 (0.13–3.68)	0.657	3.25 (1.23–8.64)	0.018	0.474

Note: Results from multi-nominal multivariate regression analyses stratified by sex.

Abbreviations: OR, odds ratio; CI, confidence interval; FEV₁% pred, forced expiratory volume in 1 second as a percentage of predicted value.