AECOPD and Nutritional Supplementation in COPD

Inclusion criteria COPD exacerbation (AECOPD) group: * Between age 45 and older * Experiencing an acute exacerbation of COPD (defined as a combination of symptoms such as increased cough, sputum purulence, shortness of breath, systemic symptoms such as fever, and a decrease in FEV1 \> 10% compared with values when clinically stable in the preceding years) and admitted at College Station Medical Center (with expected stay less than 10 days) or staying at home. * Willingness and ability to comply with the protocol, including: * Adhering to fasting state from 10 pm ± 2h onwards the day prior to each study visit * Ability to lie in supine or elevated position for 4 hours Inclusion criteria stable COPD subjects: * Ability to walk, sit down and stand up independently * Between age 45 and older * Diagnosis of moderate to very severe chronic airflow limitation and compliant to the following criteria: FEV1 \< 70% of reference FEV1 * Clinically stable condition and not suffering from a respiratory tract infection or exacerbation of their disease at least 4 weeks prior to the first test day * Shortness of breath on exertion * Willingness and ability to comply with the protocol, including: * Adhering to fasting state from 10 pm ± 2h onwards the day prior to each study visit * Ability to lie in supine or elevated position for 4 hours Inclusion criteria healthy control subjects: * Healthy male or female according to the investigator's or appointed staff's judgment * Ability to walk, s…