Table 1. Characteristics of the study population.

		Oxygen (N,%)		Medical Air (N,%)		Overall (N,%)
N		120		119		239
Male		76	63	71	60	147	62
Etiology
COPD		71	59	81	68	152	63
Restrictive lung disease		5	4	9	8	14	6
Bronchiectasis		4	3	3	2	7	3
Primary pulmonary hypertension		0	0	3	2	3	1
Primary lung cancer		18	15	15	13	33	14
Known secondary lung cancer		2	2	3	3	5	2
Pleural effusion		2	2	0	0	2	1
End stage cardiomyopathy		2	2	5	4	7	3
Other		16	13	0	0	16	7
Age	Mean (SD)	73 (11)		74 (10)		73 (10)
Baseline morning dyspnea (Day -1; 0-10 NRS)	Mean (SD)	4.5 (2.2)		4. 6 (2.4)		4.5 (2.3)
Baseline evening dyspnea (Day -1; 0-10 NRS)	Mean (SD)	4.7 (2.2)		4.7 (2.3)		4.7 (2.2)
Baseline global QOL (Day 0; 0-10 NRS)	Mean (SD)	6.2 (2.2)		5.9 (2.0)		6.0 (2.1)
MRC dyspnea functional scale
Breathless when walking at own pace^*		0	0	1	1	1	1
Breathless when walking 100 yards		54	45	59	50	113	47
Breathless when dressing or undressing		66	55	59	49	125	52
Dyspnea Exertion Scale
1: Able to walk at own pace on the level without getting out of breath		11	9	9	8	20	9
2: Becomes breathless when walking around the house or on the hospital ward on the level at own pace		54	46	50	44	104	45
3: Becomes breathless if moves around in bed or get out of bed		26	22	29	26	55	24
4: Becomes breathless when talking		24	20	23	20	47	20
5: Is breathless at rest		4	3	2	2	6	2
ECOG Performance Status
0: Fully active, able to carry on all pre-disease performance without restriction		0	0	1	1	1	0
1: Restricted in physically strenuous activity but ambulatory and able to carry out work of a light of sedentary nature, e.g., light house work, office work		40	34	29	26	69	30
2: Ambulatory and capable of all self-care but unable to carry out any work activities. Up and about more than 50% of waking hours		48	40	61	54	109	47
3: Capable of only limited self-care, confined to bed or chair more than 50% of waking hours		31	26	22	19	53	23
Regular oxygen previously prescribed		56	48	59	50	115	48
PaO₂	Mean (SD)	77 (12)		76 (12)		77 (12)
	Range	56-122		58-132		56-132
PaCO₂	Mean (SD)	39 (4)		38 (5)		39 (5)
	Range	28-51		27-51		27-51
Strata for randomization:
PaO2<=70.5		40	33	44	37	84	35
70.6<=PaO2<=80.5		37	31	38	32	75	31
80.6<=PaO2<=90.5		27	23	22	18	49	21
PaO2>=90.6		16	13	15	13	31	13
Total hours of concentrator use^**	Mean(SD)	93 (36)		98 (44)		96 (40)

This individual met the MRC eligibility criteria during enrollment.

^**

NOTE: 15 hours/day, per protocol = 105 total hours