The six minute walking test (6MWT) is a recognized clinical test to evaluate exercise capacity in different diseases and different conditions. The modalities of performance are described in International Guidelines. The usually reported measure is the distance in meters walked in 6 minutes. Despite the report of a single variable during the test is considered as a limit, changes in monitored variables are seldom analyzed together with the distance walked. In the past there have been some attempts of multifactorial evaluation of 6MWT, however up to date, there is no system considering together the changes of different variables. The investigators wonder whether a multidimensional index based on variables monitored during the 6MWT would better predict 24 month exacerbations and mortality in COPD patients.

Rationale: the six minute walking test (6MWT) is a recognized clinical test to evaluate exercise capacity in different diseases and different conditions. In COPD patients the 6MWT is a marker of severity, influenced by the severity of airway obstruction as well as of comorbidities. This test has been shown as a predictor of survival and need of hospitalization. The modalities of performance are described in International Guidelines. The usually reported measure is the distance in meters walked in 6 minutes. However, besides the pathological conditions, this result is influenced by the individual demographic and anthropometrics characteristics. The Minimal Clinically Important Difference in COPD subjects is reported to be 30 meters (m.). A decrease greater than 30 m., as compared to the previous year, is a predictor of death risk. During the test some physiological variables should be monitored such as heart rate (HR), and pulse oxymetry (SpO2). An oxyhemoglobin desaturation >4% or a SpO2 <90% during the test, are also predictors of increased risk of death or hospitalization. In addition, also the difference between the HR at baseline and that after one minute after the end of the test (recovery heart rate: HRR) seems to be a predictor of survival and COPD exacerbation rates. Despite the report of a single variable during the test is considered as a limit, changes in monitored variables are seldom analyzed together with the distance walked. In the past there have been some attempts of multifactorial evaluation of 6MWT, however up to date, there is no system considering together the changes of different variables. We wonder whether a multidimensional index based on variables monitored during the 6MWT would better predict 24 month exacerbations and mortality in COPD patients.

Objectives:

Primary Objective: To develop and validate a multidimensional index in COPD subjects with different grades of severity as assessed by the Global Initiative for Chronic Obstructive Lung disease as a predictor of 24 month exacerbation rate.

Secondary Objectives: To evaluate the predictive value of 24 month mortality. To evaluate the relationship of this index and other accepted clinical predictors.

Inclusion Criteria:

• COPD diagnosis and grades of severity as assessed by the "old" (I to IV) and "new" (A to D) GOLD guidelines (23)
• Under inhaler therapy for ≥30 days according to guidelines (23)
• Smokers or o ex-smokers, smoke history ≥10 pack/years (p/y)
• Informed Consent Signature.

Exclusion Criteria:

• Associated Comorbidities with short term severe prognosis
• Actual Cardiac Arrythmias
• Pace-maker
• Other associated respiratory diseases
• Chronic Heart Failure New York Heart Association classes III, IV.
• Use of drugs influencing the heart rate
• Changes in drug therapy in the previous 30 days
• Use of systemic steroids or antibiotics in the previous 30 days
• Unscheduled visits or admission to the Emergency Room for symptoms worsening in the previous 30 days
• Pneumonia during the previous 60 days
• Myocardial Infarction in the previous 4 months
• Subjective and objective inability to perform the 6MWT
• Inability to carry the oxygen cylinder.

Stable COPD patients assessed for Pulmonary Rehabilitation