Physiologic Variables and Functional Status Independently Predict COPD Hospitalizations and Emergency Department Visits in Patients with Severe COPD

Figures & data

Table 1 Baseline characteristics

Variable	%
Demographics
Mean age (SD)	66.5 (5.9)
Race, non-White, %	5.7
Gender, male, %	64.1
Mean body mass index (SD)	24.7 (3.5)
Medications
Inhaled short-acting β-agonist, %	87.2
Inhaled ipratropium bromide, %	82.1
Inhaled corticosteroid, %	75.7
Long-acting β-agonist, %	50.3
Methylxanthines, %	39.5
Oral corticosteroids, %	26.1
Oral short-acting β-agonist, %	2.5
Any home O2 use, %	81.3
Vaccinations
Influenza, %	93.3
Pneumococcal vaccine, %	97.5
Functional Status
Mean 6-minute walk, ft (SD)	1210 (316)
SGRQ scores, mean (SD)
Activity	79.8 (13.2)
Impact	37.6 (15.8)
Symptom	57.1 (19.3)
Total	53.6 (12.7)
Mean total SOBQ score (SD)	63.4 (18.5)
Radiology
Computed tomography
Upper lobe predominant,%	66.5
Heterogeneous, %	55.1
CXR emphysema severity score
Normal/minimally severe, %	39.2
Flat/Inverted hemidiaphragm, %	60.8
Prior Utilization in last 12 months
≥ 1COPD hospitalization, %	19.2
≥ 1COPD ER visit, %	8.9
Charlson Co-morbidity Score ≥ 1, %	34.6

SD = Standard Deviation; SGRQ = St. George's Respiratory Questionnaire; SOBQ = UCSD Shortness of Breath Questionnaire; CXR = Chest X-ray; COPD = Chronic Obstructive Pulmonary Disease; ER = Emergency Department.

*Subjects could be using no more than 20 mg prednisone (or equivalent) daily at the time of randomization.

Table 2 Baseline physiologic variables

Variable	%
Pulmonary Function Measures, Mean (SD)
FEV1 % Predicted	26.7 (7.0)
FVC, % Predicted	67.2 (15.2)
TLC, % Predicted	128.5 (15.0)
RV, % Predicted	223.3 (48.9)
DLCO, % Predicted	28.4 (9.7)
Gas Exchange
PaO2 ≤ 55 mmHg, %	21.8
PaCO2, mmHg
≤45	73.1
46–50	16.7
51–66	10.2
Exercise capacity
Maximal watts on bicycle ergometry^†
Low exercise capacity	44.6
High exercise capacity	55.4
Mean modified BODE score (SD)	5.0 (1.7)

SD = Standard deviation.

*To be eligible for NETT, patients were required to have a resting department air PaO₂ ≥ 45 mmHg (≥ 30 in Denver) and a PaCO₂ ≤ 60 (≤ 55 in Denver) prior to pulmonary rehabilitation. The baseline physiologic variables listed here were obtained after pulmonary rehabilitation was complete.

^†As defined by NETT (see text for explanation).

Figure 1 Kaplan–Meier COPD exacerbation-free survival estimates, by baseline spirometry and functional status (in tertiles).

Table 3 Candidate variables identified from univariate logistic regression to predict a COPD hospitalization or emergency department visit during the 1-year follow-up period

Variable	OR	p value
Female gender	1.37	0.09
Medication use
Oral corticosteroids	1.63	0.01
Methylxanthines	1.46	0.04
Any home O2 Use	1.76	0.03
Pulmonary Function Measures**
FEV1 % predicted	1.26	0.001
FVC, % predicted	1.10	0.002
DLCO, % predicted	1.13	0.01
Gas Exchange
PaO2 ≤ 55 mmHg	1.80	0.005
Mean 6-MW, per 180 feet^†	1.18	0.002
Low exercise capacity	1.59	0.01
Total SGRQ, per 4-point change^†	1.11	0.001
SOBQ score, per 5-point change^†	1.11	0.000
Prior Utilization in last 12 months
≥ 1COPD Hospitalization	2.42	0.000
≥ 1COPD ER visit	2.42	0.002
Charlson Co-morbidity Score ≥ 1	1.98	0.000

OR = Odds ratio, FEV₁ = Forced Expiratory Volume in 1 second, FVC = Forced vital capacity, DLCO = Diffusion capacity, PaO₂ = Arterial partial pressure of oxygen, 6-MW = 6 minute walk, SGRQ = St. George's Respiratory Questionnaire, SOBQ = UCSD Shortness of Breath Questionnaire. *Only variables significant at p < 0.10 level presented in this table. **For each 5-point change in pulmonary function (e.g., from 40% predicted to 35% predicted). ^†Change corresponding to the minimum clinically important difference in each measure.

Table 4 Final multivariate logistic regression models comparing 3 different functional status measures to predict a COPD hospitalization or emergency department visit during the 1-year follow-up period

Variables	Model 1		Model 2		Model 3
	OR	95% CI	OR	95% CI	OR	95% CI
Pulmonary function
FEV1	1.16	(1.00,1.34)	1.19	(1.03,1.37)	1.18	(1.02,1.37)
PaO2 < 55 mmHg	1.67	(1.08,2.59)	1.68	(1.09,2.61)	1.67	(1.08,2.59)
Functional Status
SOBQ total**	1.08	(1.02,1.14)
SGRQ total^†			1.07	(1.01,1.14)
6-Minute Walk^† †					1.08	(0.96,1.21)
Prior Utilization
≥1Prior COPD Hosp	2.07	(1.32,3.25)	2.10	(1.34,3.29)	2.13	(1.37,3.33)
≥1Prior COPD ER Visit	2.05	(1.13,3.75)	2.07	(1.14,3.77)	2.18	(1.20,3.96)
Co-morbidity
Charlson-Deyo score ≥ 1	1.69	(1.14,2.49)	1.64	(1.11,2.41)	1.62	(1.10,2.39)
Goodness of Fit test^‡, χ^2 and p-value	568.9	p = 0.63	597.5	p = 0.56	592.3	p = 0.56
AUC
Original sample	0.70		0.69		0.69
Optimism/Bias	−0.02		−0.02		−0.01
Validated	0.68		0.67		0.68

OR = Odds ratio, CI = Confidence interval, FEV₁ = Forced Expiratory Volume in 1 second, PaO₂ = Arterial partial pressure of oxygen, SGRQ = St. George's Respiratory Questionnaire, SOBQ = UCSD Shortness of Breath Questionnaire, COPD = Chronic Obstructive Pulmonary Disease, AUC = Area under the receiver operator characteristic curve, ER = Emergency Department.

*per 5-point change in percent predicted FEV₁(e.g., from 40% to 35% predicted).

**per 5-point increase (worsening) in SOBQ score.

^†per 4-point increase (worsening) in SGRQ score.

^{† †}per 180-foot change in 6-Minute Walk.

^‡Hosmer-Lemeshow Goodness-of-fit statistic.