Body Mass Index and Lung Function in Hospitalized Severe AECOPD Patients: Investigating Nonlinear Associations and the Role of Hemoglobin

Cong Zhang,1 Wenhao Ling,1 He Pan,2 Rui Bai,3 Li He1 1Department of Respiratory and Critical Care Medicine, Jingzhou Hospital Affiliated to Yangtze University, Jingzhou, Hubei, People’s Republic of China; 2Department of Laboratory Medicine, Jingzhou Hospital Affiliated to Yangtze University, Jingzhou, Hubei, People’s Republic of China; 3Department of Pulmonary Oncology, Zhongnan Hospital of Wuhan University, Wuhan, Hubei, People’s Republic of ChinaCorrespondence: Li He, Department of Respiratory and Critical Care Medicine, Jingzhou Hospital Affiliated to Yangtze University, Jingzhou, People’s Republic of China, Email [email protected] Rui Bai, Department of Pulmonary Oncology, Zhongnan Hospital of Wuhan University, Wuhan, People’s Republic of China, Email [email protected]: Chronic obstructive pulmonary disease (COPD) is a leading cause of global morbidity and mortality. Patients hospitalized with severe acute exacerbations of COPD (AECOPD) represent a high-risk group with poor outcomes and accelerated lung function decline. Body mass index (BMI) shows inconsistent associations with lung function across populations, and its role in AECOPD remains unclear. Understanding this relationship may improve clinical management. Hemoglobin (Hb), essential for oxygen transport, may further influence this association through physiological mechanisms. This study aimed to explore the relationship between BMI and lung function in hospitalized patients with severe AECOPD and to assess whether BMI influences length of hospital stay (LOHS), while evaluating the potential modifying role of Hb.Methods: A retrospective, single-center cross-sectional study was conducted among 579 patients hospitalized for severe AECOPD from 2021 to 2023. Data on BMI, lung function, Hb levels, and LOHS were collected. Nonlinear and threshold effect analyses were used to explore associations between BMI and lung function or LOHS. Subgroup analyses assessed the modifying effect of Hb.Results: BMI exhibited a nonlinear positive association with FEV1, FVC, FEV1% predicted, and FVC% predicted. Thresholds were identified at 25.39 kg/m² for FEV1, 26.23 kg/m² for FEV1% predicted, 21.67 kg/m² for FVC, and 22.19 kg/m² for FVC% predicted. The association was more pronounced in patients with higher Hb levels. No significant association was found between BMI and LOHS, suggesting that other factors such as infection severity, comorbidities, or treatment strategies may may exert greater influence.Conclusion: A nonlinear, inverse L-shaped association was observed between BMI and lung function, further modified by Hb levels. These findings highlight the importance of individualized treatment and stratification strategies in severe AECOPD. Future longitudinal studies are needed to validate these observations.Keywords: BMI, lung function, AECOPD, hemoglobin, LOHS