Table 2.

Changes in survey scores over 8 weeks, according to treatment assignment

	Baseline (mean ± SD)	Study end(mean ± SD)	Change (mean ± SD)	N-acetylcysteine–placebo
				Mean difference (95% CI)	P-value	Adjusted mean difference (95% CI)	P-value
SGRQ
Symptoms
Placebo (n=22)	69.3±17.7	59.5±21.2	−9.8±17.8	6.3 (−4.6, 17.3)	0.25	1.6 (−10.4, 13.5)	0.79
N-acetylcysteine (n=23)	54.2±17.4	50.7±20.3	−3.5±18.6
Activity
Placebo (n=22)	69.8±21.9	66.1±21.5	−3.7±14.5	−0.3 (−8.7, 8.2)	0.95	−1.1 (−8.5, 6.3)	0.76
N-acetylcysteine (n=23)	70.4±20.9	66.4±16.9	−4.0±13.6
Impact
Placebo (n=22)	42.3±22.5	34.8±22.8	−7.5±20.1	3.0 (−7.6, 13.6)	0.57	−0.4 (−10.0, 9.2)	0.93
N-acetylcysteine (n=23)	36.9±19.9	32.4±17.9	−4.5±14.9
Total
Placebo (n=22)	55.5±20.0	48.4±20.7	−7.1±16.1	3.2 (−5.3, 11.8)	0.45	0.1 (−7.8, 8.1)	0.97
N-acetylcysteine (n=23)	49.6±16.9	45.8±14.9	−3.9±12.1
CBSAS
Placebo (n=22)	22.5±8.3	19.6±8.0	−2.8±5.2	0.6 (−2.4, 3.6)	0.69	−0.8 (−3.8, 2.2)	0.60
N-acetylcysteine (n=23)	17.6±7.5	15.4±7.2	−2.2±4.8
SF-36
Physical
Placebo (n=22)	35.6±7.5	36.2±9.2	0.6±7.6	−1.9 (−6.0, 2.1)	0.34	−0.6 (−4.4, 3.2)	0.75
N-acetylcysteine (n=23)	38.4±6.5	37.1±6.3	−1.3±5.8
Mental
Placebo (n=22)	49.5±10.8	47.9±13.5	−1.6±12.3	2.7 (−3.5, 8.8)	0.38	3.2 (−2.8, 9.1)	0.29
N-acetylcysteine (n=23)	50.2±10.9	51.2±12.6	1.0±7.6

Notes: Results presented as mean ± SD. Adjusted mean differences in change scores estimated in the regression model for change score using intervention, baseline outcome measure, age, sex, and percentage predicted FEV₁ as explanatory variables.

Abbreviations: CBSAS, Chronic Bronchitis Symptoms Assessment Scale; FEV₁, forced expiratory volume in 1 second; SF-36, Short Form-36 Health Survey; SGRQ, St George’s Respiratory Questionnaire; SD, standard deviation; CI, confidence interval.