Groups of 25 patients with COPD with moderate-to-severe airflow obstruction, 25 patients with moderate-to-severe CHF, and 36 healthy age-matched volunteers were studied. All pulmonary patients had COPD according to American Thoracic Society guidelines9–
and chronic airflow limitation, defined as measured FEV1 < 70% of reference FEV1. Furthermore, patients with COPD had irreversible obstructive airway disease (< 10% improvement of FEV1 predicted baseline after β2-agonist inhalation). Patients with COPD were in clinically stable condition and not having respiratory tract infection or exacerbation of their disease at least 4 weeks prior to the study. Other exclusion criteria for the COPD group were concomitant confounding diseases like malignancies, GI disorders, severe endocrine disorders, CHF, or recent surgery. The cardiac patients had CHF based on clinical symptoms according to the Framingham criteria,10
LVEF < 45%, and were in clinically stable condition. All patients with CHF were controlled at the outpatient clinic of the university Hospital of Maastricht. The origins of heart failure were idiopathic (n = 7), ischemic (n = 8), valvular disease (n = 1), multiple origins (n = 6), and miscellaneous (n = 3). They were all receiving extensive medication regiments: angiotensin-converting enzyme inhibitors (N = 24), diuretics (n = 24), β-blockers (n = 16), and nitrates (n = 16). Warfarin was used by 20 patients. Exclusion criteria for the CHF group were noncardiac disease with life expectancy < 1 year, episodes of heart failure within the previous 2 months, unstable angina pectoris, scheduled for percutaneous transluminal coronary angioplasty or coronary artery bypass grafting, operable valvular disease, kidney failure (creatinine level > 250 μmol/L), restrictive cardiomyopathy, hypertrophic cardiomyopathy, primary pulmonary hypertension, diabetes mellitus, COPD, psychiatric disorder, or correctable cause of heart failure. The healthy age-matched control subjects were volunteers recruited through advertisement in a local newspaper. They underwent a physical examination by a physician to ensure that they were free from significant pulmonary or cardiac disease. Written informed consent was obtained from all subjects, and the study was approved by the medical ethical committee of the University Hospital Maastricht (Maastricht, the Netherlands).