Predictors of exacerbation frequency in chronic obstructive pulmonary disease
- Hui Yang†1, 2,
- Pingchao Xiang†2,
- Erming Zhang2,
- Wei’An Guo2,
- Yanwei Shi2,
- Shuo Zhang2 and
- Zhaohui Tong1Email author
© Yang et al.; licensee BioMed Central Ltd. 2014
Received: 27 April 2013
Accepted: 17 January 2014
Published: 8 April 2014
Exacerbations of chronic obstructive pulmonary disease (COPD) are sporadic, acute worsening of symptoms. Identifying predictors of exacerbation frequency may facilitate medical interventions that reduce exacerbation frequency and severity. The objective of this study was to determine predictors of exacerbation frequency and mortality.
A total of 227 COPD patients were enrolled in a prospective clinical study between January 2000 and December 2011. Reported exacerbations were recorded for the year preceding enrollment and annually thereafter, and patients were grouped by median annual exacerbation frequency into those experiencing infrequent exacerbations (less than one exacerbation annually) and frequent exacerbations (one or more exacerbation annually). Patients experiencing frequent exacerbations were further divided into those experiencing moderately frequent exacerbations (fewer than two exacerbations per year) and severely frequent exacerbations (two or more exacerbations per year). The rate of clinical relapse and survival was recorded over a 10-year period. The mean of follow-up time was 5.15 years per patient.
For patients experiencing infrequent, moderately frequent, and severely frequent exacerbations, median exacerbations in the year preceding enrollment were 0.0, 0.5, 1.0, respectively, and more frequent exacerbations correlated with lower baseline forced expiratory volume in one second (FEV1) (0.81 L, 0.75 L, and 0.66 L, respectively), higher comorbidity (70.7%, 75.0%, and 89.4%, respectively), and greater NPPV use during hospitalization (16.4%, 35.9% and 51.1%, respectively). FEV1 declined and mortality increased with increasing exacerbation frequency.
Exacerbation frequency can be used to generate discreet patient subpopulations, supporting the hypothesis that multiple COPD phenotypes exist and can be used in patient risk stratification.
KeywordsChronic obstructive pulmonary disease Exacerbation Forced expiratory volume Comorbidity Positive pressure ventilation
Chronic obstructive pulmonary disease (COPD), characterized by difficulty breathing due to chronic bronchitis or emphysema, is one of the most common lung conditions observed in clinical practice, the fourth leading cause of death in the world . An exacerbation of COPD is defined as acute worsening in the severity of a patient’s symptoms, including baseline dyspnea and cough, that warrants a change in medication or medical intervention . Exacerbations have been linked to disease-associated morbidity and mortality, placing significant strain on medical facilities, increasing resource burden, and driving up ongoing healthcare costs . To better allocate healthcare resources, exacerbations can be classified by symptom type and severity, and by the frequency of incidents requiring intervention .
Exacerbation frequency varies significantly among patients [5, 6], and more frequent exacerbations are linked to more rapidly declining lung function and higher mortality . The importance of exacerbation prediction has recently been recognized in the application of effective and aggressive prevention strategies , including antibiotic therapies that are designed to reduce exacerbation frequency and severity . While major advances have been made in the past decade, measureable prognostic factors predicting exacerbation risk in COPD patients remain undefined.
The most reliable predictor of increasing exacerbation frequency is conventionally considered to be a patient’s previous history of exacerbations , potentially indicating a definable phenotype of exacerbation susceptibility. Most published research on COPD exacerbations are large interventional studies [9, 10] with highly variable exacerbation definitions [8–10]. Thus, few data have been collected that can reliably indicate clinically measurable prognostic risk factors for COPD exacerbation frequency and associated clinical outcomes.
To better assess the prognostic factors associated with COPD frequency, we followed a 227-member cohort of COPD patients over a 10-year period. We identified predictors of exacerbation frequency and generated a mechanism for improved clinical classification of COPD patients by exacerbation frequency. This classification may improve the efficacy of strategically applied prophylactic interventions.
Study design and patient groups
A total of 227 COPD patients were recruited consecutively between 1 January 2000 and 31 December 2006 for inclusion in a study of exacerbation frequency ranging from the inclusion start date to 31 December 2011 at the Outpatient Department of Respiration of the Shougang Hospital of Beijing University (Beijing, China). The study protocol was approved by the Medical ethics committee of Shou-Gang Hospital Affiliated to Peking University. All patients provided written informed consent for participation.
Inclusion and exclusion criteria
Inclusion criteria included a COPD diagnosis, defined as a forced expiratory volume in 1 second (FEV1) of < 80% of the predicted value after bronchodilator use and a ratio of FEV1 to forced vital capacity (FVC) of < 70% after bronchodilator use. We recruited participants between the ages of 45 and 85 years who were in a stable condition, having experienced no exacerbations in the month preceding enrollment, and who could provide medical records indicating the number of times in the preceding year they had been hospitalizations as a result of COPD. Patients who did not consent to long-term follow-up or were diagnosed with another condition that limited life expectancy were excluded from the analysis.
Data collection and follow-up
During initial clinical examinations, patient demographics were recorded, including sex, age, height, weight, body mass index (BMI), and smoking history. Clinical characteristics were recorded for each patient, including lung function, drug history (including bronchial-dilating agents, glucocorticoids), comorbidities, number of hospitalization as a result of COPD exacerbations in the year preceding enrollment, and every year throughout the follow-up period, and use of long-term oxygen therapy (LTOT), home mechanical ventilation (HMV) used for chronic hypercapnia of COPD, and non-invasive positive pressure ventilation (NPPV, used for exacerbations accompanied by acute respiratory failure) during hospitalization. Follow-up was conducted by telephone interview and review of appropriate medical records every 6 months until the end of the study. Quint et al. have previously determined that patient recall was a sufficiently accurate tool for stratification of patients into those experiencing frequent and infrequent exacerbations .
Lung function was assessed using a volumetric storage spirometer (HP 47-804; Hewlett-Packard, Waltham, MA, USA) to measure arterial carbon dioxide tension (PaCO2); arterial oxygen tension (PaO2); forced expiratory volume in one second (FEV1); and forced vital capacity (FVC) at baseline (year 0) and thereafter at 2-year intervals for the first 4 years. GOLD grades were calculated according to the Global Initiative for Chronic Obstructive Lung Disease.
At the end of follow-up, the Charlson comorbidity index was computed and analyzed. The Charlson Index assigns a score to each underlying condition proportional to its corresponding disease-related risk of death . The arithmetical sum of scores for individual comorbidities was used as an index for each patient.
Statistical analyses were performed using SPSS version 17.0 (SPSS Inc., Chicago, IL, USA). Continuous variables were presented as means ± standard deviation (SD) or as medians and interquartile ranges by data distribution. One-way ANOVA was used to compare exacerbation frequency. Chi-square tests with Pearson’s, continuity correction, or Fisher’s Exact test were used for binary variables. Logistic regression analysis was used to identify independent predictors of frequent exacerbations. Univariate survival analysis was performed using Kaplan-Meier analysis (log-rank test). Multivariate COX proportional hazards regression models were used to identify independent predictors of mortality. Relative risk and 95% confidence intervals (CIs) were presented. P values less than 0.05 were considered statistically significant.
Clinical and demographic characteristics
Baseline of clinical and demographic characteristics among groups according to exacerbation frequency
Group 1 (n = 116)
Group 2A (n = 64)
Group 2B (n = 47)
Total (n = 227)
Age (mean ± SD, yrs)
71.78 ± 6.36
71.02 ± 7.24
72.19 ± 7.30
71.65 ± 6.80
Height (mean ± SD, cm)
169.6 ± 2.32
171.2 ± 3.19
170.7 ± 2.56
170.9 ± 3.03
Weight (mean ± SD, kg)
67.06 ± 4.10
67.60 ± 3.78
71.20 ± 3.98
68.90 ± 2.75
BMI (mean ± SD, kg/m2)
23.58 ± 3.31
23.05 ± 4.30
24.42 ± 3.68
23.60 ± 3.70
Current smoker, %
Numbers of preceding year exacerbationa
0 (0 to 1.0)
0.5 (0 to 2.0)
1.0 (0 to 2.0)
0 (0 to 1.0)
GOLD 1, %
GOLD 2, %
GOLD 3, %
GOLD 4, %
FEV1 (mean ± SD, L)b
0.81 ± 0.36
0.75 ± 0.33
0.66 ± 0.29
0.76 ± 0.34-
FEV1 (mean ± SD, % predicted)
38.76 ± 16.90
37.61 ± 17.08
34.49 ± 11.91
37.55 ± 16.07-
FVC, (mean ± SD, L)c
1.50 ± 0.54
1.42 ± 0.49
1.27 ± 0.53
1.43 ± 0.53-
pH (mean ± SD)
7.40 ± 0.04
7.40 ± 0.04
7.40 ± 0.04
7.40 ± 0.04-
PaCO2 (mean ± SD, mmHg)d
48.03 ± 9.97
51.35 ± 10.45
49.78 ± 12.04
49.33- ± 10.61
PaO2 (mean ± SD, mmHg)
67.42 ± 11.67
67.10 ± 14.30
65.56 ± 13.01
66.94 ± 12.70-
Cor pulmonale, %e
Cardiovascular disease, % (n)
70.0 (159) -
Cerebrovascular disease, % (n)
28.6 (65) -
Diabetes mellitus, % (n)
14.1 (32) -
Neoplasms, % (n)
8.4 (19) -
Osteoporosis, % (n)
3.1 (7) -
Arrhythmia, % (n)
2.6 (7) -
1 (0 to 3.0)
1 (0 to 4.0)
1 (0 to 3.6)
1 (1.0-2.0) -
Charlson index (mean ± SD)g
5.30 ± 1.77
5.33 ± 1.94
5.62 ± 1.53
5.37 ± 1.77-
Medicine at home, %
LTOT at home, %
NPPV in hospitalization, %*h
The mean follow-up time was 5.15 years per patient. The number of exacerbations in the year before recruitment into this study, FEV1, FVC, PaCO2, cor pulmonale, comorbidity, and the Charlson Index score of patients varied significantly between groups (P < 0.05, Table 1).
Factors associated with increased exacerbation frequency
More frequent exacerbations were significantly associated with lower FEV1 and FVC, a higher frequency of exacerbation in the preceding year, higher PaCO2, higher incidence of cor pulmonale, and a higher rate of comorbidities (P < 0.05, Table 1). The most common comorbidity was cardiovascular disease, though cerebrovascular disease, diabetes mellitus, and neoplasm were also observed.
Scoring assessments indicate exacerbation frequency
Comorbidity and exacerbation frequency
Logistic analysis of predictors for severely frequent exacerbations (Group 2B)
95% CI for RR
Exacerbations in the year preceding enrollment
The rate of NPPV use by GOLD 4 patients (40.8%) was significantly higher than the rate of NPPV use by GOLD 3 (28.4%) or GOLD 2 (10.3%) patients (all P < 0.05). NPPV use in Group 2A (35.9%) and Group 2B (51.1%) was significantly higher than NPPV use in Group 1 (16.4%, OR 2.864, 95% CI 1.410 to 5.819, and OR 5.327, 95% CI 2.507 to 11.326, respectively, Table 2). Increased exacerbation frequency was significantly associated with higher levels of NPPV use (P < 0.05, Table 2).
Forced expiratory volume in one second is related to exacerbation frequency
Exacerbation history is related to exacerbation frequency
A history of previous exacerbations was also significantly associated with increased exacerbation frequency (P < 0.05, Table 2).
Mortality increases with increasing exacerbation frequency
Deaths were due to respiratory failure (51.1%), comorbidities (46.7%), and unknown factors (2.2%). Of those deaths related to comorbidities (63 in total), 38.1% were related to infections, 25.4% were related to neoplasms, including lung cancer (62.5%), cerebrovascular disease (15.9%), cardiovascular disease (14.3%), and pulmonary embolism (6.3%).
Patients in Group 2B and 2A had mortality rates approximately 2.6 fold and 2.0 fold greater, respectively, than patients in Group 1 (95% CI 1.253 to 5.457; 95% CI 1.084 to 3.868). Significantly different 5- and 10-year cumulative survival rates were observed in Groups 1 (58% and 41%), 2A (58% and 41%) and 2B (29% and 23%) (P = 0.003, Table 1). More patients in Group 1 died as a result of a comorbidity than respiratory failure (51.7% versus 39.7%), whereas the majority of patients in group 2A died of respiratory failure (60.5% versus 34.9%). Patients in Group 2B died of respiratory failure and comorbidities at a similar rate (50.0% versus 44.1%).
Verifying the prognostic factors for mortality
Cox analysis of independent prognostic factors for all chronic obstructive pulmonary disease (COPD) patients
95.0% CI for RR
A group of COPD patients that were susceptible to multiple exacerbations was identified and the associations between these occurrences and potential prognostic factors including FEV1, exacerbation history, NPPV use, and comorbidities were determined. Logistic analysis of exacerbation frequency during a follow-up period confirmed that the rate of exacerbations reported in the year preceding enrollment was an independent predictor of more frequent exacerbations in the future. Patients with moderately frequent and severely frequent exacerbations had mortality rates approximately 2.6 fold and 2.0 fold greater, respectively, than those experiencing infrequent exacerbations, and COX analysis confirmed that exacerbation frequency was an independent prognostic factor for elevated mortality. These findings highlight the need for improved identification and stratification of COPD patients with frequent exacerbations for more in-depth monitoring and treatment with more aggressive therapeutic strategies.
The study of COPD exacerbations is complicated by the varying definition of exacerbations employed. Studies have applied a variety of cutoffs related to the median number of exacerbations per study group [3, 13, 18], a relative measurement that makes it difficult to compare data between studies. In an attempt to mediate these discrepancies, some studies have applied a fixed model for assessing exacerbation frequency, wherein ‘frequent exacerbations’ are defined as those occurring two or more times a year [10, 19]. This model was applied in this study, and additionally, we specified that the exacerbation events must be separated by 14 days and require hospitalization.
Several models for the prediction of COPD exacerbations have been explored over the past decade. Hurst et al.  reported that a reliable predictor of exacerbations across all GOLD stages was a previous history of exacerbations. Numerous additional studies have confirmed that previous COPD exacerbations are a risk factor for new exacerbations, independent of COPD severity and other clinical manifestations [3, 5, 7, 8]. Similarly, within the population we studied, exacerbation frequency preceding enrollment was found to be an independent predictor of exacerbation frequency during the follow-up period.
We have identified some additional prognostic factors that can be used to stratify COPD patient risk; FEV1, comorbidities, and NPPV use, along with exacerbation history, were identified as independent predictors of elevated exacerbation frequency. Similarly, the TORCH (Toward a Revolution in COPD Health) trial  reported a negative association between exacerbation frequency and declining FEV1, and David et al. reported that higher exacerbation frequency was associated with significantly lower baseline post-bronchodilator FEV1. Conversely, Kirby et al.  determined that FEV1 was not a significant clinical predictor of frequent exacerbations. We can conclude that the number of exacerbations does not increase linearly with FEV1 decline, but is influenced by multiple factors.
Clinical manifestations of systemic inflammation are often observed in parallel with COPD exacerbations . Extra-pulmonary factors may play a role in COPD-related declining lung function. As reported for cardiovascular exacerbations, patients with higher numbers of concomitant disorders may be more prone to exacerbations leading to frequent hospitalization . These findings were confirmed in a case–control study of severe COPD patients that indicated patients with frequent exacerbations also experienced more frequent cardiovascular comorbidities , consistent with the elevated rate of cardiovascular and other comorbidities reported for patients experiencing frequent exacerbations in this study. However, because these observations were not found to be statistically significant, further study will be required to verify this association.
While this report identifies the association between several prognostic factors and increased exacerbation frequency in COPD patients, further study is required before broad clinical recommendations can be made.
A history of frequent exacerbations, lower FEV1, and multiple comorbidities were independent prognostic factors for exacerbation frequency, in a 10-year study of 227 COPD patients. Patients who experienced two or more exacerbations annually were at a greater risk for early mortality than patients with less frequent exacerbations. Thus, these patients should be considered candidates for aggressive monitoring and therapy to mediate COPD disease progression and to reduce exacerbation frequency and severity. Furthermore, the stratification of patients in this study supports the hypothesis that discreet phenotypes exist that can be used to determine patient risk in clinical settings.
Body mass index
Chronic obstructive pulmonary disease
Forced expiratory volume in one second
Forced vital capacity
Global Initiative for Chronic Obstructive Lung Disease
Home mechanical ventilation
Long-term oxygen therapy
Non-invasive positive pressure ventilation
Arterial carbon dioxide tension
Arterial oxygen tension.
This study was supported by the Beijing High-grade Talents Health Technology Fund (2011-2-06).
- World Health Report. Geneva: World Health Organization; Available from URL: 2000 http://www.who.int/whr/2000/en/statistics.htm.
- GOLD Executive and Science Committees: Global strategy for the diagnosis, management and prevention of chronic obstructive pulmonary disease: GOLD Executive Summary updated 2009. http://www.gold-copd.org
- Vestbo J, Hurd SS, Agustí AG, Jones PW, Vogelmeier C, Anzueto A, Barnes PJ, Fabbri LM, Martinez FJ, Nishimura M, Stockley RA, Sin DD, Rodriguez-Roisin R: Global strategy for the diagnosis, management, and prevention of chronic obstructive pulmonary disease: GOLD executive summary. Am J Respir Crit Care Med 2013, 187: 347–365. 10.1164/rccm.201204-0596PPPubMedView ArticleGoogle Scholar
- Anzueto A: Impact of exacerbations on COPD. Eur Respir Rev 2010, 19: 113–118. 10.1183/09059180.00002610PubMedView ArticleGoogle Scholar
- Donaldson GC, Seemungal TA, Bhowmik A, Wedzicha JA: Relationship between exacerbation frequency and lung function decline in chronic obstructive pulmonary disease. Thorax 2002, 57: 847–852. 10.1136/thorax.57.10.847PubMedPubMed CentralView ArticleGoogle Scholar
- Hurst JR, Vestbo J, Anzueto A, Locantore N, Mullerova H, Tal-Singer R, Miller B, Lomas DA, Agusti A, Macnee W, Calverley P, Rennard S, Wouters EF, Wedzicha JA: Susceptibility to exacerbation in chronic obstructive pulmonary disease. N Engl J Med 2010, 363: 1128–1138. 10.1056/NEJMoa0909883PubMedView ArticleGoogle Scholar
- Albert RK, Connett J, Bailey WC, Casaburi R, Cooper JA Jr, Criner GJ, Curtis JL, Dransfield MT, Han MK, Lazarus SC, Make B, Marchetti N, Martinez FJ, Madinger NE, McEvoy C, Niewoehner DE, Porsasz J, Price CS, Reilly J, Scanlon PD, Sciurba FC, Scharf SM, Washko GR, Woodruff PG, Anthonisen NR: Azithromycin for prevention of exacerbations of COPD. N Engl J Med 2011, 365: 689–698. 10.1056/NEJMoa1104623PubMedPubMed CentralView ArticleGoogle Scholar
- Donaldson GC, Wedzicha JA: COPD exacerbations 1: epidemiology. Thorax 2006, 61: 164–168. 10.1136/thx.2005.041806PubMedPubMed CentralView ArticleGoogle Scholar
- Calverley PM, Anderson JA, Celli B, Ferguson GT, Jenkins C, Jones PW, Yates JC, Vestbo J: Salmeterol and fluticasone propionate and survival in chronic obstructive pulmonary disease. N Engl J Med 2007, 356: 775–789. 10.1056/NEJMoa063070PubMedView ArticleGoogle Scholar
- Tashkin DP, Celli B, Senn S, Burkhart D, Kesten S, Menjoge S, Decramer M: A 4-year trial of tiotropium in chronic obstructive pulmonary disease. N Engl J Med 2008, 359: 1543–1554. 10.1056/NEJMoa0805800PubMedView ArticleGoogle Scholar
- Donaldson GC, Seemungal T, Jeffries DJ, Wedzicha JA: Effect of temperature on lung function and symptoms in chronic obstructive pulmonary disease. Eur Respir J 1999, 13: 844–849. 10.1034/j.1399-3003.1999.13d25.xPubMedView ArticleGoogle Scholar
- Burge S, Wedzicha JA: COPD exacerbations: definitions and classifications. Eur Respir J Suppl 2003, 41: 46s-53s.PubMedView ArticleGoogle Scholar
- Hurst JR, Donaldson GC, Quint JK, Goldring JJ, Baghai-Ravary R, Wedzicha JA: Temporal clustering of exacerbations in chronic obstructive pulmonary disease. Am J Respir Crit Care Med 2009, 179: 369–374. 10.1164/rccm.200807-1067OCPubMedView ArticleGoogle Scholar
- Szafranski W, Cukier A, Ramirez A, Menga G, Sansores R, Nahabedian S, Peterson S, Olsson H: Efficacy and safety of budesonide/formoterol in the management of chronic obstructive pulmonary disease. Eur Respir J 2003, 21: 74–81. 10.1183/09031936.03.00031402PubMedView ArticleGoogle Scholar
- Calverley PMA, Pauwels R, Vestbo J, Jones PW, Pride N, Gulsvick A: Combined salmeterol and fluticasone in the treatment of chronic obstructive pulmonary disease. Lancet 2003, 361: 449. 10.1016/S0140-6736(03)12459-2PubMedView ArticleGoogle Scholar
- Quint JK, Donaldson GC, Hurst JR, Goldring JJ, Seemungal TR, Wedzicha JA: Predictive accuracy of patient-reported exacerbation frequency in COPD. Eur Respir J 2011, 37: 501–507. 10.1183/09031936.00035909PubMedView ArticleGoogle Scholar
- Charlson M, Szatrowski TP, Peterson J, Gold J: Validation of a combined comorbidity index. J Clin Epidemiol 1994, 47: 1245–1251. 10.1016/0895-4356(94)90129-5PubMedView ArticleGoogle Scholar
- Seemungal TA, Donaldson GC, Paul EA, Bestall JC, Jeffries DJ, Wedzicha JA: Effect of exacerbation on quality of life in patients with chronic obstructive pulmonary disease. Am J Respir Crit Care Med 1998, 157: 1418–1422. 10.1164/ajrccm.157.5.9709032PubMedView ArticleGoogle Scholar
- Miravitlles M, Ferrer M, Pont A, Zalacain R, Alvarez-Sala JL, Masa F, Verea H, Murio C, Ros F, Vidal R: Effect of exacerbations on quality of life in patients with chronic obstructive pulmonary disease: a 2 year follow up study. Thorax 2004, 59: 387–395. 10.1136/thx.2003.008730PubMedPubMed CentralView ArticleGoogle Scholar
- Celli BR, Thomas NE, Anderson JA, Ferguson GT, Jenkins CR, Jones PW, Vestbo J, Knobil K, Yates JC, Calverley PM: Effect of pharmacotherapy on rate of decline of lung function in chronic obstructive pulmonary disease: results from the TORCH study. Am J Respir Crit Care Med 2008, 178: 332–338. 10.1164/rccm.200712-1869OCPubMedView ArticleGoogle Scholar
- Kirby SE, Dennis SM, Jayasinghe UW, Harris MF: Patient related factors in frequent readmissions: the influence of condition, access to services and patient choice. BMC Health Serv Res 2010, 10: 216. 10.1186/1472-6963-10-216PubMedPubMed CentralView ArticleGoogle Scholar
- Donaldson GC, Seemungal TA, Patel IS, Bhowmik A, Wilkinson TM, Hurst JR, Maccallum PK, Wedzicha JA: Airway and systemic inflammation and decline in lung function in patients with COPD. Chest 2005, 128: 1995–2004. 10.1378/chest.128.4.1995PubMedView ArticleGoogle Scholar
- Niewoehner DE, Lokhnygina Y, Rice K, Kuschner WG, Sharafkhaneh A, Sarosi GA, Krumpe P, Pieper K, Kesten S: Risk indexes for exacerbations and hospitalizations due to COPD. Chest 2007, 131: 20–28. 10.1378/chest.06-1316PubMedView ArticleGoogle Scholar
- Soler JJ, Sanchez L, Roman P, Martinez MA, Perpina M: Risk factors of emergency care and admissions in COPD patients with high consumption of health resources. Respir Med 2004, 98: 318–329. 10.1016/j.rmed.2003.04.001PubMedView ArticleGoogle Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited.