Burden and Characteristics of Severe Chronic Hypoxemia in a Real-World Cohort of Subjects with COPD

Figures & data

Table 1 Comparison Between COPD Subjects with and without Severe Hypoxemia

	All	PaO2<60 mmHg	PaO2≥60 mmHg	p
n, %	887	146 (16%)	741 (84%)
Age, yr	64 [57; 72]	65 [58; 74]	64 [57; 72]	NS
Sex, M/F	653/234	110/36	543/198	NS
Smoking, pack-yr	40 [25; 59]	39 [24; 75]	41 [25; 59]	NS
BMI <18.5 kg.m-²	81 (9%)	21 (14%)	60 (8%)	0.02
BMI > 30 kg.m-²	201 (23%)	31 (21%)	170 (23%)	NS
Exacerbations in previous year, n	1 [0; 2]	1 [0; 3]	1 [0; 3]	NS
History of asthma	125 (14%)	13 (9%)	112 (15%)	0.049
Hypertension	344 (39%)	58 (40%)	286 (39%)	NS
Coronary artery disease	123 (14%)	23 (16%)	100 (14%)	NS
Left heart failure	101 (11%)	17 (12%)	84 (11%)	NS
Diabetes	126 (14%)	24 (16%)	102 (14%)	NS
Obstructive SleepApnea	86 (10%)	16 (11%)	70 (10%)	NS
mMRC dyspnea grade	2 [1; 3]	3 [2; 3]	2 [1; 3]	<0.0001
paO2, mmHg	71 [63; 79]	56 [52: 59]	73 [65; 80]	<0.0001
paCO2, mmHg	40 [37; 43]	44 [40; 50]	39 [36; 43]	<0.0001
pH	7.42 [7.40; 7.44]	7.42 [7.40; 7.45]	7.42 [7.40; 7.44]	0.6614
FEV1, % predicted	48 [33; 63]	35 [25; 47]	51 [36; 65]	<0.0001
FVC, % predicted	82 [68; 98]	71 [58; 92]	83 [69; 99]	<0.0001
RV, % predicted	166 [131; 209]	186 [143; 229]	161 [131; 205]	0.0063
TLC, % predicted	113 [100; 129]	117 [101; 131]	113 [100; 128]	NS
RV/TLC, %	57 [48; 65]	64 [54; 69]	56 [48; 63]	<0.0001
DLCO, mL/min/mmHg	13.8 [9.2; 18.9]^a	8.0 [5.6; 10.9]^b	14.8 [11.0; 19.7]^c	< 0.0001
SGRQ	37 [23; 52]	57 [42–68]	45 [32; 58]	<0.0001
6MWD	400 [305; 470] ^d	305 [266; 393]^e	410 [320; 480]^f	<0.0001
3-year mortality	79 (9%)	20 (14%)	59 (8%)	0.026

Notes: 887 COPD subjects were included (146 having PaO₂<60 mmHg and 741 having PaO₂ ≥60mmHg). Data are n (%) or median [interquartiles]. Missing values are^a n=549, ^bn=97, ^cn=460, ^d n=370, ^en=71, ^fn=299.

Abbreviations: ABG, arterial blood gas; BMI, body mass index; FEV1, forced expiratory volume in 1 second; FVC, forced vital capacity; OSA, obstructive sleep apnea; mMRC, modified medical research council; NS, non-significant; SGRQ, Saint Georges respiratory questionnaire; TLC, total lung capacity; RV, residual volume; 6MWD, 6-minute walking distance.

Figure 1 Distribution of PaO₂ (A) and relationships between PaO2 and PaCO2 (B). 887 COPD subjects were included. Values are in mmHg.

Figure 2 Relationships between PaO₂ and FEV₁, and distribution of COPD subjects for severe hypoxemia and severe airflow limitation. 887 COPD subjects were included. High PaO₂/high FEV₁ are in the right and upper part of the graph. High PaO₂/low FEV₁ are in the left and upper part of the graph. Low paO₂/high FEV₁ are in the right and lower part of the graph. Low PaO₂/high FEV₁ are in the left and lower part of the graph. Values are in mmHg or %.

Table 2 Comparison Between COPD Subjects with and without Severe Hypoxemia, with or without Severe Airflow Obstruction

	PaO2<60 mmHg FEV1<50% (1)	PaO2<60 mmHg FEV1≥50% (2)	PaO2≥60 mmHg FEV1≥50% (3)	PaO2≥60 mmHg FEV1<50% (4)
n, %	115 (13%)	31 (3%)	386	355 (40%)
Age, yr	64 [57; 73]	71 [64; 77]^#,+	65 [58; 73]	63 [57; 70]
Sex, M/F	85/30	25/6	271/115	272/83
Smoking, pack-yr	39 [25; 56]	40 [20; 63]	40 [25; 55]	41 [25; 61]
BMI <18,5 kg.m-²	20 (17%)	1 (3%)^+	17 (4.4%)	43 (12%)
BMI > 30 kg.m-²	22 (19%)	9 (29%)	109 (29.2%)	61 (17%)
Exacerbations in previous year, n	1 [0; 3]	1 [0; 3]	1 [0; 2]	2 [1; 3]
History of asthma	13 (11%)	0 (0%)	54 (14%)	58 (16%)
Hypertension	45 (39%)	13 (42%)	154 (40%)	132 (37%)
Coronaryartery disease	16 (14%)	7 (23%)	56 (15%)	44 (12%)
Heart failure	10 (9%)	7 (23%)	43 (11%)	41 (11%)
Diabetes	15 (13%)	9 (29%)^+	48 (12%)	54 (15%)^#
Obstructive SleepApnea	14 (12%)	2 (6.5%)	44 (12%)	24 (7%)
mMRC scale	3 [2; 3]	2 [2; 3]	1 [1; 2] ^#	2 [1; 3] ^#
FEV1, % predicted	30 [23; 39]	61 [55; 71]^+	64 [57; 74]	35 [27; 42]
FVC, % predicted	69 [54; 81]	99 [76; 110]^+	95 [84; 107]	71 [59; 82]
RV, % predicted	202 [164; 244]	124 [92; 155] ^+	142 [121; 170]	197 [155; 246] ^#
TLC, % predicted	122 [107; 135]	94 [85; 117] ^+	109 [98; 122]	119 [104; 134] ^#
RV/TLC, %	65 [60; 71]	48 [42; 54]^+	50 [44; 57]	63 [56; 60]
DLCO, mL/min mmHg	7.7 [4.9; 10.6]^a	8.6 [7.9; 14.6]^+, b	16.8 [13.2; 22.5]^c	12.2 [7.8; 16.4]^d, #
PaCO2	45 [42; 53]	39 [35; 42]	38 [35; 41]	40 [37; 43]
SGRQ	58 [46; 70]	44 [39; 59] ^+	38 [26; 51]	54 [41; 64]
6MWD	303 [255; 372] ^e	315 [283; 399] ^f	430 [370; 500]^g	374 [300; 445] ^h, #
3-year mortality	15 (13%)	5 (16%)	18 (5%)	41 (12%)^#

Notes: 887 COPD subjects were included (115 having PaO₂<60 mmHg and FEV1<50%, 115 having PaO₂<60 mmHg and FEV1≥50%, 386 having PaO₂≥60 mmHg and FEV1≥50% and 355 having PaO₂≥60 mmHg and FEV1<50%). n (%) or median [interquartiles] ⁺1 versus 2, ^#2 versus 4. Missing values are ^cn=220, ^dn=240, ^an=76, ^bn=21, ^gn=163, ^h n=136, ^en=57, ^fn=14.

Abbreviations: BMI, body mass index; FEV_1, forced expiratory volume in 1 second; FVC, forced vital capacity; mMRC, modified medical research council; SGRQ, Saint Georges respiratory questionnaire; TLC, total lung capacity; RV, residual volume; 6MWD, 6-minute walking distance.

Figure 3 Repartition of PaO₂ according to GOLD stage 2007 1 to 4 (A–D, respectively) or according to CART classification 1 to 5 (E–I, respectively) (with a cut-off at 60 mmHg, (8)). 887 COPD subjects were included.