Depressive status explains a significant amount of the variance in COPD assessment test (CAT) scores

Figures & data

Table 1 Demographic and clinical characteristics of the study population

Variable	CAT score category				All (N=684)
	0–10 (n=69)	11–20 (n=228)	21–30 (n=282)	31–40 (n=105)
Age (years)	65.8±10.5	68.7±9.4	69.5±9.1*	68.8±8.9	68.7±9.3
Sex (men)	57 (82.6)	197 (87.6)	227 (81.4)	89 (85.8)	570 (84.1)
Active smoker	16 (23.2)	44 (19.5)	60 (21.6)	25 (24.3)	145 (21.4)
COPD duration (years)	7.6±6.2	10.1±7.6	12.1±6.6	15.8±9.4***	11.5±7.7
FVC (mL)	3,291±824	2,959±883	2,812±927	2,858±994***	2,917±922
FVC (%)	78.5±16.9	69.8±16.1	69.2±17.4	68.4±18.1***	70.2±17.2
FEV1 (mL)	1,876±616	1,725±739	1,630±719	1,619±759***	1,685±725
FEV1 (%)	58.0±15.3	53.5±15.8	51.4±16.6	48.6±17.5***	52.3±16.3
FEV1/FVC	56.5±11.8	55.8±11.2	53.5±12.3	53.0±13.8**	5.5±12.2
Cough (yes)	34 (49.3)	171 (76.7)	255 (91.7)	102 (97.1)***	562 (83.3)
Expectoration (yes)	30 (43.5)	137 (62.0)	222 (89.4)	93 (89.4)***	482 (72.3)
Dyspnea (yes)	56 (81.2)	220 (96.5)	279 (99.6)	105 (100)***	660 (96.8)
Exacerbations in the previous year (yes)	47 (68.1)	192 (84.2)	268 (95.0)	91 (86.7)***	598 (87.4)
Oxygen therapy at home (yes)	3 (4.6)	29 (13.4)	87 (32.0)	39 (40.2)***	158 (24.3)
BODEx	1.4±1.4	2.2±1.5	3.4±1.8	4.2±1.6***	3.0±1.9
MMSE	28.8±1.8	27.0±3.5	25.7±4.0	23.9±5.7***	26.2±4.2
BDI score	3.5±3.3	6.0±3.9	10.8±5.5	14.4±7.4***	9.0±6.2
Depression (yes)	18 (26.1)	142 (62.3)	255 (90.4)	101 (96.2)***	516 (75.4)
Severe depression (yes)	1 (1.4)	9 (3.9)	54 (19.1)	40 (38.1)***	104 (15.2)
Charlson index	0.8±1.1	1.0±1.0	1.6±1.4	2.4±2.0***	1.4±1.4
Minutes walked per day	78.4±39.3	69.9±49.8	56.9±41.5	40.8±29.8***	61.2±44.2

Notes: Data are presented as mean ± SD or n (%).

* Differences in age were significant for the comparison between CAT 0–10 and CAT 21–30, p<0.05,

** p<0.01,

*** p<0.001 (Fisher’s test or ANOVA).

Abbreviations: ANOVA, analysis of variance; BDI, Beck Depression Inventory; BODEx, body mass index, airflow obstruction, dyspnea, and exacerbations; CAT, COPD assessment test; FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; MMSE, Mini-Mental State Examination.

Figure 1 Distribution of CAT scores among participants.

Abbreviation: CAT, COPD assessment test.

Figure 2 Correlation between CAT score and MMSE scores (A), BDI scores (B), post-bronchodilator FEV₁ (% predicted) (C), and post-bronchodilator FEV₁/FVC (D).

Abbreviations: BDI, Beck Depression Inventory; CAT, COPD assessment test; FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; MMSE, Mini-Mental State Examination.

Table 2 Multivariate regression analysis for CAT score variance

Variable	Model 1	Model 2	Model 3
BDI score	0.73 (0.04)***	0.65 (0.04)***	0.68 (0.05)***
MMSE score	−0.23 (0.06)***	−0.14 (0.06)	−0.13 (0.07)*
Age		0.006 (0.02)	−0.07 (0.03)**
Sex		−0.31 (0.66)
Post-bronchodilator		NA	−0.06 (0.02)***
FVC (%)
Post-bronchodilator		−0.03 (0.02)
FEV1 (%)
Post-bronchodilator		NA	−0.9 (0.02)***
FEV1/FVC
Dyspnea		−6.90 (1.35)***	−6.60 (1.44)***
Previous exacerbations		−1.20 (0.72)
Charlson index		0.66 (0.18)**	0.60 (0.20)**
r^2	0.40	0.43	0.45
p-value	<0.001	<0.001	<0.001

Notes: Data are presented as beta value (SE).

* p<0.05,

** p<0.01,

*** p<0.001. Model 1 only includes BDI and MMSE scores; Model 2 includes the whole set of variables, except FVC and FEV₁/FVC due to collinearity; Model 3 stepwise automatic selection of variables with a p-value <0.15.

Abbreviations: BDI, Beck Depression Inventory; CAT, COPD assessment test; FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; MMSE, Mini-Mental State Examination; NA, not assessed; SE, standard error.

Table 3 Univariate regression analysis for CAT score variance

Variable	Beta value (SE)	r^2
BDI score	0.80 (0.04)***	0.38
BODEx	2.06 (0.15)***	0.23
MMSE score	−0.70 (0.07)***	0.14
Charlson index	1.99 (0.19)***	0.13
Minutes walked per day	−0.04 (0.007)***	0.07
Post-bronchodilator FEV1 (%)	−0.07 (0.02)***	0.02
Post-bronchodilator FEV1/FVC	−0.07 (0.02)**	0.01

Note:

** p<0.01,

*** p<0.001.

Abbreviations: BDI, Beck Depression Inventory; BODEx, body mass index, airflow obstruction, dyspnea, and exacerbations; CAT, COPD assessment test; FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; MMSE, Mini-Mental State Examination; SE, standard error.