Chronic obstructive pulmonary disease (COPD) is a lung disease characterized by respiratory problems and poor airflow with dyspnea and cough being the main symptoms. Acute exacerbations of COPD (AECOPD) are the most important events for patients with COPD that have a negative impact on patients´ quality of life, accelerate disease progression, and can result in hospital admissions and death. It is of major clinical importance to determine predictors of an AECOPD and to identify patients who are at high risk for developing an acute exacerbation and/or to detect the beginning of or prevent an ongoing acute exacerbation as early as possible. Until now, research in the field of AECOPD has gathered and analyzed data only after manifestation of AECOPD until recovery and most of them used a retrospective study design. Therefore, the aim of this prospective trial is to collect clinical data in patients prior to the first visible clinical signs of an AECOPD to investigate potential early predictors of an AECOPD.

In total, 355 COPD patients will be included prospectively to this study during a 3-week inpatient pulmonary rehabilitation programme at the Schoen Klinik Berchtesgadener Land, Schoenau am Koenigssee, (Germany). All patients will be closely monitored from admission to the study. Measures of lung function, blood samples, breath sampling, exercise tests, physical activity monitoring, cardiac parameters, quality of life and a symptom diary will be recorded regularly. Prior knowledge from this programme suggest that about 15% of patients will develop an AECOPD during this observational phase. If a patient develops an AECOPD there will be a comprehensive diagnostic assessment to differentiate between cardiac, pulmonary or cardio-pulmonary reasons for the AECOPD and to identify the type of exacerbation. The clinical diagnosis and management of an AECOPD will be determined by a pulmonologist according to criteria of international guidelines within the first 24h after the onset of clinical symptoms suggestive of an exacerbation. Collected clinical data from the days prior to AECOPD will be analyzed comprehensively to identify parameters with high prediction power for AECOPD. Furthermore, patients will perform follow-up measures at 6, 12 and 24 months following the initial observational phase (PR phase).

A wide range of predictor screening methods will be applied to identify significant predictors including cross tabulation tables, correlations, generalized linear models, mixed models, generalized estimation equation models and various predictor screening methods based on variable selection algorithms.

Study objectives Primary endpoint: To prospectively identify potential early, respiratory and/ or cardiac clinical predictors, laboratory parameters, breath print analyses and/ or changes in lung function and physical activity prior to an AECOPD in COPD patients.

Secondary endpoint(s):

1. To identify potential mechanisms explaining the nature and composition of an acute exacerbation in COPD patients
2. To identify and differentiate patterns of acute COPD exacerbation versus cardiac failure in COPD patients
3. To investigate the potential role of an electronic-nose to capture exhaled breath metabolomic profiles for the early detection of an acute exacerbation in COPD patients ("COPD pre exacerbation breath print")
4. To identify parameters influencing mortality and other adverse events in the total study cohort at 6, 12 and 24 months follow up

Inclusion Criteria:

• confirmed diagnosis of Chronic Obstructive Pulmonary Disease according to Global Association for Obstructive Lung Disease stage II to IV
• the ability to follow the rehabilitation protocol
• provided written informed consent

Exclusion Criteria:

- current primary diagnosis of asthma

Patients with Chronic Obstructive Pulmonary Disease that are referred to an inpatient pulmonary rehabilitation program at the reference center.