Comparison of exercise capacity in COPD and other etiologies of chronic respiratory failure requiring non-invasive mechanical ventilation at home: retrospective analysis of 1-year follow-up

Figures & data

Figure 1 Consort diagram showing patient enrollment, follow-up and analysis.

Abbreviations: ABG, arterial blood gas analysis; COPD, chronic obstructive pulmonary disease; DPLD, diffuse parenchymal lung disease; ICU, intensive care unit; KS, kyphoscoliosis; NIMV, non-invasive mechanical ventilation; OHS, obesity hypoventilation syndrome; 6MWT, 6-minute walking test; SPASA, Sureyyapasa Chest Disease And Thoracic Surgery Teaching And Research Hospital.

Table 1 Baseline characteristics of chronic respiratory failure patients having non-invasive ventilation at home followed at the outpatient clinic between 2011 and 2012

	COPD, n=37	OHS, n=34	Kyphoscoliosis, n=20	DPLD, n=14
Age, years, mean ± SD	65±10	65±8	46±10	62±12
Female, %	8.1	50	45	21.4
BMI, kg/m^2, mean ± SD	25±6	41±6	27±7	27±6
HNIV parameters, mean ± SD
IPAP, cm H2O	24±3	23±3	22±5	21±5
EPAP, cm H2O	5.3±0.7	5.8±0.8	5.3±0.6	5.5±0.7
Therapy duration, hour/day	6.7±1.9	6.4±2.4	5.9±1.8	5.8±1.4
Charlson comorbidity index, mean ± SD	4±1	4±1	2±2	3±1

Abbreviations: BMI, body mass index; COPD, chronic obstructive lung disease; DPLD, diffuse parenchymal lung disease; EPAP, expiratory positive airway pressure; HNIV, home non-invasive ventilation; IPAP, inspiratory positive airway pressure; OHS, obesity hypoventilation syndrome; SD, standard deviation.

Table 2 Baseline measurements and 1-year change in 6-minute walking test in chronic respiratory failure patients having non-invasive mechanical ventilation

	COPD, n=37			OHS, n=34			Kyphoscoliosis (KS), n =20			DPLD, n=14			P-value*
	Baseline	Δ in 1 year		Baseline	Δ in 1 year		Baseline	Δ in 1 year		Baseline	Δ in 1 year
	Mean ± SD	Mean	95% CI	Mean ± SD	Mean	95% CI	Mean ± SD	Mean	95% CI	Mean ± SD	Mean	95% CI
6MWD,a m	332±99	10.43	−4.3 to 25.2	315±74	−13.9	−31.9 to 3.96	373±90	47.25	15.66–78.83	354±76	25.5	6.34–44.65	0.01
Ideal 6MWD, m	550±100	−6.04	−22.02 to 9.92	418±77	−8.84	−13.26 to −4.41	628±93	−5.4	−9.17 to−1.64	542±100	−9.86	−14.3 to −5.37	0.95
Predicted,b %	61.3±15.9	1.09	−1.55 to 3.73	75.7±14.5	−2.39	−6.48 to 1.69	61.2±17	7.55	3.31 to 11.79	67.1±17.3	6.1	2.27–9.93	0.01
LLN, m	398±15.9	−0.83	−20.36 to 18.7	272±71	−10.31	−16.14 to −4.47	482±92	−5.9	−9.65 to −2.16	392±98	−9.64	−14.3 to −4.96	0.71

Notes:

a Baseline vs 1-year values: P=0.11 for COPD; P=0.21 for OHS; P=0.004 for KS; P=0.03 for DPLD, via paired Wilcoxon test.

b Baseline vs 1-year values: P=0.23 for COPD; P=0.38 for OHS; P=0.003 for KS; P=0.01 for DPLD, via paired Wilcoxon test.

* P-values for the comparison of mean Δ values among groups with different diagnoses. Significant for 6MWD upon post hoc Tukey HSD: KS vs COPD (P=0.049) and KS vs OHS (P<0.001). Significant for predicted % upon post hoc Tukey HSD: OHS vs KS (P=0.002) and OHS vs DPLD (P=0.027).

Abbreviations: CI, confidence interval; COPD, chronic obstructive lung disease; DPLD, diffuse parenchymal lung disease; HSD, honesty of significance difference; LLN, lower limit of normal range; OHS, obesity hypoventilation syndrome; SD, standard deviation; Δ, change; 6MWD, 6-minute walking distance.

Table 3 Pulmonary function testing and arterial blood gas measurements in chronic respiratory failure patients having non-invasive mechanical ventilation

	COPD, n=37			OHS, n=34			Kyphoscoliosis, n =20			DPLD, n=14			P-value*
	Baseline	Δ in 1 year		Baseline	Δ in 1 year		Baseline	Δ in 1 year		Baseline	Δ in 1 year
	Mean ± SD	Mean	95% CI	Mean ± SD	Mean	95% CI	Mean ± SD	Mean	95% CI	Mean ± SD	Mean	95% CI
pH	7.42±0.05	−0.03	−0.05 to −0.007	7.44±0.04	−0.002	−0.04 to 0.004	7.45±0.05	−0.017	−0.04 to 0.012	7.43±0.05	−0.011	−0.04 to 0.02	0.76
PaCO2, mmHg	49±8	0.56	−0.52 to 4.23	46±8	1.85	−0.52 to 4.23	52±11	−2.85	−8.08 to 2.38	49±8	0.01	−5.7 to 5.7	0.27
PaO2/FiO2	264±107	25.77	−11.36 to 62.91	287±58	17.93	−5.98 to 41.84	300±85	14.20	−26.04 to 54.45	277±81	38.37	−0.47 to 77.22	0.76
HCO3, mmol	31.5±5.8	−2.68	−4.85 to −0.71	31.3±5.6	−0.57	−2.63 to 1.47	36.5±13.8	−5.88	−12.7 to 1.15	31.8±4.3	−0.55	−4.58 to 3.48	0.14
SpO2%	89±8	2.48	0.2 to 4.76	92±3	0.41	−0.8 to 1.63	92±4	−0.65	−7.81 to 6.51	92±4	2.42	0.23 to 4.62	0.46
FEV1, mL	661±257	78.7	−12.04 to 169.54	1,133±645	−82.27	−192.94 to 28.39	858±516	−21.6	−70.36 to 113.69	890±402	−25.7	−182.1 to 130.67	0.11
FEV1, %	27±11	1.78	−1 to 4.56	50±20	−2.38	−7.59 to 2.86	25±8	3.58	−1.51 to 8.68	34±15	0.14	−6.55 to 6.83	0.31
FVC, mL	1,184±459	−52.18	−189.88 to 85.5	1,461±725	−138.63	−283.24 to 5.97	1,018±609	−140.83	−487.42 to 205.76	1,113±504	60	−159.96 to 279.98	0.46
FVC, %	37±14	−0.5	−4.58 to 3.58	52±18	11.13	−21.29 to 43.57	24±7	3.08	−2.24 to 8.41	34±15	2.78	−4.85 to 10.42	0.76
FEV1/FVC	68±21	0.4	−4.94 to 5.75	77±13	1.77	−1.66 to 5.20	92±18	0.83	−4.07 to 5.73	80±10	−4.92	−13.06 to 3.2	0.42

Note:

* P-values for the comparison of mean Δ values among groups with different diagnoses by ANOVA test.

Abbreviations: COPD, chronic obstructive lung disease; DPLD, diffuse parenchymal lung disease; FEV₁, forced expiratory volume in 1 second; FiO₂, fraction of inspired oxygen; FVC, forced vital capacity; HCO₃, bicarbonate; OHS, obesity hypoventilation syndrome; PaCO₂, partial carbon dioxide pressure; PaO₂, partial oxygen pressure; SpO₂, oxygen saturation; ANOVA, analysis of variance; CI, confidence interval; SD, standard deviation; Δ, change.

Figure 2 Box plots for delta 6-minute walking test in meters in four diagnosis groups.

Abbreviations: o, outliers; Min, minimum value excluding outliers; Max, maximum value excluding outliers; M, median; T, third quartile; L, first quartile; Δ, change; 6MWD, 6-minute walking distance; COPD, chronic obstructive lung disease; OHS, obesity hypoventilation syndrome; DPLD, diffuse parenchymal lung disease.

Table 4 Pre-test and post-test scores for dyspnea and fatigue at baseline and 1-year 6MWT in study groups

	COPD, n=37	OHS, n=34	Kyphoscoliosis, n=20	DPLD, n=14	P-value*
Post-discharge 6MWT
Baseline
Dyspnea scorea
Pre-test	1 (1–2)	1 (0–2)	0 (0–1)	2 (0–2)	0.18
Post-test	2 (1–3)	2 (0–4)	1 (1–3)	2 (1–3)	0.67
VAS-F scorea
Pre-test	1 (0–2)	1 (0–2)	0 (0–1)	0 (0–2)	0.50
Post-test	2 (0–3)	2 (1–3)	1 (0–3)	1 (0–3)	0.30
1-year
Dyspnea score
Pre-test	1 (0–2)	1 (0–2)	0 (0–1)	1 (0–1)	0.80
Post-test	3 (1–5)	1 (0–2)	1 (0–2)	1 (0–2)	0.003
VAS-F score
Pre-test	0 (0–2)	0 (0–2)	0 (0–1)	0 (0–1)	0.527
Post-test	1 (0–3)	1 (0–2)	1 (0–2)	1 (0–1)	0.442

Notes: Data are shown as median (25th–75th percentile).

a Dyspnea and fatigue scores may be between 0 and 10. Higher scores indicate higher severity.

* Kruskal– Wallis test.

Abbreviations: COPD, chronic obstructive lung disease; DPLD, diffuse parenchymal lung disease; OHS, obesity hypoventilation syndrome; VAS-F, Visual Analog Scale to Evaluate Fatigue Severity; 6MWT, 6-minute walking test.

Table 5 Data on body mass index alteration, emergency admission, hospital stay, and the interval between last exacerbation and 1-year assessment in study groups

	COPD, n=37	OHS, n=34	Kyphoscoliosis, n=20	DPLD, n=14	P-value
Body mass index (kg/m^2)
Baseline, mean ± SD	25.0±6.0	41.0±6.0	27.0±7.0	27.0±6.0	0.001a
1-year, mean ± SD	26.0±6.0	42.0±6.0	28.0±7.0	28.0±6.0	0.001a
Δ, mean ± SD	0.0±2.0	0.0±2.0	0.0±2.0	1.0±1.0	0.96a
Emergency admission
Present, n (%)	18 (17.1)	13 (12.4)	5 (4.8)	4 (3.8)	0.298b
Number of admissions, mean ± SD	2.0±1.0	2.0±1.0	1.0±0.0	2.0±1.0	0.312a
Hospital stay
Present, n (%)	12 (11.4)	4 (3.8)	2 (1.9)	2 (1.9)	0.081b
Number of hospitalizations, mean ± SD	2.0±1.0	2.0±0.0	1.0±0.0	2.0±1.0	0.698a
Length of stay (days), mean ± SD	10.0±5.0	11.0±3.0	7.0±3.0	10.0±4.0	0.839a
Days from last exacerbation to 1-year assessment, mean ± SD	204.0±50.0	210.0±52.0	260.0±13.0	234.0±61.0	0.134a

Notes:

a ANOVA test.

b χ² test.

Abbreviations: COPD, chronic obstructive lung disease; DPLD, diffuse parenchymal lung disease; OHS, obesity hypoventilation syndrome; SD, standard deviation; Δ, change; ANOVA, analysis of variance.

Table 6 Demographic and clinical characteristics of patients with COPD according to the presence of emergency or hospital admission

	COPD (n=37)
	Emergency admission			Hospital admission
	Present	Absent	P-value	Present	Absent	P-value
Age (years), mean ± SD	63±10	66±10	0.34a	66±8	64±11	0.53a
Sex, n (%)
Female	1 (5.6)	2 (10.5)		1 (8.3)	2 (8)
Male	17 (94.4)	17 (89.5)		11 (91.7)	23 (92)
BMI (kg/m^2), mean ± SD
Baseline	23±6	27±6	0.048a	24±4	26±7	0.30a
1-year	24±6	28±6	0.07a	25±5	26±7	0.45a
FEV1 (mL), mean ± SD
Baseline	689±307	633±202	0.53a	614±276	687±250	0.44a
1-year	785±302	830±483	0.74a	697±296	864±432	0.23a
PaCO2 (mmHg), mean ± SD
Baseline	48±8	50±9	0.47a	48±8	50±9	0.58a
1-year	50±6	50±9	0.90a	51±7	49±8	0.67a
6MWD (m), mean ± SD
Baseline	364±65	301±116	0.05a	359±51	319±114	0.25a
1-year	373±71	314±108	0.06a	366±34	331±113	0.31a
Δ6MWD	8.56±50.82	12.21±38.58	0.800a	6.58±45.25	12.28±44.74	0.72a

Note:

a Independent sample t-test.

Abbreviations: BMI, body mass index; COPD, chronic obstructive lung disease; FEV₁, forced expiratory volume in 1 second; PaCO₂, partial carbon dioxide pressure; 6MWD, 6-minute walking distance; Δ6MWD, difference between first and second 6-minute distance with 1-year interval; SD, standard deviation.

Table 7 Linear regression analysis for Δ6MWD (m) with adjusted variables and COPD diagnosis as the reference

Variable	Linear regression coefficient	95% CI	P-value
COPD	–	–	–
OHS	−24.48	−48.74 to −0.21	0.048
Kyphoscoliosis	26.94	−3.79 to 57.66	0.09
DPLD	16.70	−8.51 to 41.91	0.19
Age	−0.80	−1.69 to 0.08	0.07
Male	−4.23	−25.45 to 17.00	0.69
6MWD, m	−0.16	−0.26 to 0.05	0.003
Baseline FEV1, mL	0.014	−0.005 to 0.033	0.14
PaCO2 first, mmHg	0.43	−0.53 to 1.39	0.38

Abbreviations: CI, confidence interval; COPD, chronic obstructive lung disease; DPLD, diffuse parenchymal lung disease; FEV₁, forced expiratory volume in 1 second; OHS, obesity hypoventilation syndrome; PaCO₂, partial carbon dioxide pressure; Δ6MWD, difference between first and second 6-minute distance with 1-year interval; 6MWD, 6-minute walking distance.